**Role of Sensory Evaluation in Consumer Acceptance of Plant-Based Meat Analogs and Meat Extenders: A Scoping Review**

### **Martina Fiorentini, Amanda J. Kinchla and Alissa A. Nolden \***

Department of Food Science, University of Massachusetts Amherst, Amherst, MA 01003, USA; mfiorentini@umass.edu (M.F.); amanda.kinchla@foodsci.umass.edu (A.J.K.)

**\*** Correspondence: anolden@umass.edu

Received: 14 August 2020; Accepted: 18 September 2020; Published: 22 September 2020

**Abstract:** Growing demand for sustainable food has led to the development of meat analogs to satisfy flexitarians and conscious meat-eaters. Successful combinations of functional ingredients and processing methods result in the generation of meat-like sensory attributes, which are necessary to attract non-vegetarian consumers. Sensory science is a broader research field used to measure and interpret responses to product properties, which is not limited to consumer liking. Acceptance is evaluated through hedonic tests to assess the overall liking and degree of liking for individual sensory attributes. Descriptive analysis provides both qualitative and quantitative results of the product's sensory profile. Here, original research papers are reviewed that evaluate sensory attributes of meat analogs and meat extenders through hedonic testing and/or descriptive analysis to demonstrate how these analytical approaches are important for consumer acceptance. Sensory evaluation combined with instrumental measures, such as texture and color, can be advantageous and help to improve the final product. Future applications of these methods might include integration of sensory tests during product development to better direct product processing and formulation. By conducting sensory evaluation, companies and researchers will learn valuable information regarding product attributes and overall liking that help to provide more widely accepted and sustainable foods.

**Keywords:** sensory evaluation; consumer acceptance; descriptive analysis; meat analog; meat extender; plant-based; alternative protein; imitation meat

#### **1. Introduction**

#### *1.1. Background: The Need for Sustainable Alternatives to Meat*

The meat industry is currently facing one of the biggest challenges of the past century: to meet the growing demand for animal products by providing high-quality protein without exceeding the critical limit of natural resources. Current predictions estimate that the world population will reach 9 billion people by 2050 [1] combined with the rising trend of meat consumption due to income increase in industrialized countries [2], which indicates that demand for animal-source foods is likely to double by 2050. This presents an alarming threat to our planet, as meat production is an intensive and unsustainable process, causing environmental problems such as deforestation, pollution, damage to hydrogeological reserves, and loss of biodiversity [3]. The livestock sector alone is responsible for 14.5% of human-made greenhouse gas emissions [4] and uses almost 30% of the world's fresh water resources [5]. Another motivating factor is the issues surrounding animal welfare [6], with concerns regarding the unethical practices of factory farming as well as the excessive use of antibiotics used to fight new infections caused by potentially deadly pathogens.

Replacing meat with sustainable alternative proteins is one promising strategy to reduce meat consumption [7]. The environmental gains of relying on non-animal protein sources such as plants, insects, fungi, and algae, are significant. A complete switch to non-animal proteins in the human diet would reduce the use of natural resources currently dedicated to the livestock sector by 35–50% [8]. In Western countries, plant-derived proteins are more popular than other alternative proteins [9]. Soy products like tofu and tempeh, which originate from Asian countries, have been commercially available in the West since the 1960s and are now accepted by vegetarians and vegan consumers who avoid eating meat for ethical, environmental, or health reasons [10]. However, such products are not as popular among meat-eaters and flexitarians due to their low sensory appeal [11]. Many food companies have joined the alternative protein movement and promote sustainable eating by developing plant-based products with meat-like sensory attributes, often referred to as meat analogs, plant-based, or imitation meat. On a food processing level, recreating the texture and flavor of muscle meat starting from plant proteins has proved to be a challenge, often attributed to production of off-flavors typically by legumes and a lower saturated fat content that is responsible for tenderness and juiciness [12]. While there are many different processing methods to prepare meat analogs, one top-down strategy is high-moisture wet extrusion, which is highly successful in achieving a desirable structure, most resembling animal proteins [13]. Another strategy to achieve desirable texture and flavor while also reducing meat consumption is by partially replacing animal protein with plant-derived extenders. This is a common practice adopted by the food industry to improve the economical, functional, sustainability, and nutritional profile of processed meats [14].

Overconsumption of red meat in Western countries contributes to the development of cardiovascular disease due to the high saturated fat content [15]. This represents a major public health issue, specifically in the United States, where heart disease is the leading cause of death [16]. However, consumption trends observed in the last decade reveal that most Americans do not seem to be reducing their intake of red meat [2]. Identifying high-quality meat alternatives that mimic traditional meats may more effectively appease consumers without compromising the sensory qualities of meat products. Process optimization and new technologies aimed at utilizing novel plant-proteins are essential to the product development of meat analogs. Sensory evaluation, in the context of meat analogs, provides important information regarding the selection of processing methods and use of novel ingredients to achieve meat-like sensory attributes by providing both quantitative and qualitative data on taste, flavor, texture, and appearance.

#### *1.2. Role of Sensory Evaluation in Consumer Acceptance of Meat Analogs*

For meat analogs to successfully replace meat in the everyday diet, these novel products must be first accepted by the public in terms of overall liking. Sensory evaluation plays multiple roles in predicting consumer acceptance of meat analogs as this is not only influenced by the product's sensory characteristics but also by person-related factors. These depend on the ethical aspects, political values, and ecological welfare involved in the production and can act as either drivers or barriers to acceptance of meat analogs. Data collected from a consumer survey in the U.K. and The Netherlands show that, while consumers are typically aware of the ethical and political implications of their food choices, purchase intention is ultimately driven by the product's sensory attributes [11]. More specifically, the unfamiliarity with novel foods can alter expectations that may negatively impact sensory perception and overall liking [17]. To reduce consumer uncertainty to meat analogs, these are often marketed with slogans such as "tastes like meat" so that consumers can relate to their previous experience and form favorable expectations on the product's performance. Sensory evaluation methods can gather data regarding consumers' perceptions beyond the oral perception of foods. It is important to identify which product characteristics are drivers of product liking, while also taking into consideration differences between person-related factors. Integrating data of this kind with results from sensory evaluation and instrumental measurements provide a more accurate description of the physiochemical and sensory properties of meat analogs.

While the sensory properties of a food product play a collective role in forming positive expectations both before and during consumption, some may be more important than others. According to a 2019 survey of US adults, 86% of consumers considered taste to be the major driver of purchase intention [18]. In the same light, unpleasant or unexpected taste can represent a barrier to acceptance. In fact, non-vegetarians seem to be reluctant to try meat analogs due to the belief that consuming healthy products might compromise taste [19]. This obstacle can be overcome by developing products that meat-eaters will enjoy not only in terms of their individual sensory properties but also in the meal context in which they will be consumed. This includes other food components in the dish, such as rice, vegetables, and soups, as well as seasonings, spices, and sauces. A successful interaction of these ingredients depends on their sensory attributes. For instance, before consumption, shape, color, and appearance have a greater influence on consumer acceptance compared to flavor and texture [20]. This is because visual cues define the appropriateness of the meal, which is dictated by the cultural aspects of eating certain foods and by the individual preferences of the consumers. By contrast, consumers' perception of flavor and texture of meat analogs are minimized to a certain extent, due to other ingredients in the meal that can have either a masking or enhancing effect. Sensory evaluation can help to increase consumer acceptance of meat analogs by investigating the complex interaction between factors that are known to affect meal appropriateness with the goal to understand the best way to market these products based on their sensory properties.

#### *1.3. Sensory Evaluation Methods*

This narrative review focuses on two main categories of sensory evaluation that are summarized in Table 1. Consumer acceptability tests, also called hedonic of affective tests, assess the degree of liking of a product based on its sensory appeal. Untrained participants perform the test, usually greater than 100 participants, who are screened for product usage [21]. A common way to assess acceptability is through hedonic scales where the participants indicate how much they like or dislike the sample in terms of a specific sensory property, such as appearance, flavor, taste, and texture, and can also include overall liking/acceptance. The most commonly used scale is the 9-point hedonic scale that ranges from "like extremely" to "dislike extremely" [21]. Other scales include the visual analog scale (VAS), a non-marked, anchored line, and the "just about right" (JAR) scale, which is used to adjust the proportions of certain ingredients that can alter the intensity of a sensory characteristic (e.g., spiciness, saltiness). A set of check-all-that-apply (CATA) terms can also be used to collect hedonic responses. This is a format in which respondents are presented with a list of terms and asked to select all those that apply to each sample. The list of terms can be either generated by a group of trained panelists or it can be derived from the available literature. In other instances, the CATA method can be used to estimate the intensity of a specific attribute by examining the frequency in which the attribute is experienced; however, in the current review, the study utilizing this method has selected terms that are hedonic in nature and, therefore, grouped with acceptability tests. Descriptive sensory analysis provides a more detailed assessment of the product's sensory profile. It determines both a qualitative and quantitative measurement of the intensities of each sensory attribute. Descriptive analysis techniques include the Flavor Profile®, Quantitative Descriptive Analysis®, Texture Profile®, and Sensory Spectrum® [21]. Trained panelists, often 8–12, undergo extensive training on the relevant attributes [21]. Following training, panelists independently rate intensity of each attribute. These methods provide different information regarding the sensory profile of the product. Consumer data identifies which sensory attributes are needed to increase overall liking, whereas data from descriptive analysis is more accurately quantified and can significantly contribute to the direction of product development. An appropriate selection of the method is important for obtaining the desired sensory information to improve the final product.


**Table 1.** Summary of sensory evaluation methods used to evaluate plant-based meat analogs.

#### *1.4. Organization and Scope of the Review*

The application of consumer studies and descriptive analysis provides useful information about the sensory profile and consumer acceptance of foods and beverages. To the authors' knowledge, there has not been a literature review on the application of these sensory evaluation methods to meat analogs and extended meat products. This narrative review summarizes the literature evaluating the sensory attributes of meat analogs and meat extenders. Specifically, it focuses on studies that involve consumers' evaluation of products that uses hedonic and/or descriptive analysis methods. Here, the review focuses on plant-based products as these are the most commercially available and are preferred by consumers [22,23], rather than other alternative protein sources (e.g., insect, fungi, and algae). Moreover, the review includes studies of extended meat products where partial replacement of meat protein was at least 30% following the analysis of consumer data revealing a preference for hybrid products with a 50:50 ratio of plant-based to meat ingredients [24]. By reviewing the available literature, the goal is to show the advantage of evaluating the sensory properties of meat analogs to predict consumer acceptance by understanding the factors that affect hedonic preference. The purpose of this review is to summarize the changes that occur in sensory attributes resulting from the integration and innovation of processing techniques of novel plant-proteins. There is an opportunity to build a greater understanding of the impact of novel plant-proteins and processing technology on the taste, flavor, and texture profile. Achieving desirable meat-like qualities will help to increase consumers' acceptance with the long-term goal of reducing the consumption and production of animal livestock that improves human health and environmental sustainability.

#### **2. Search Criteria Methods**

Articles were searched from Web of Science and Google Scholar using keywords and restriction on publication year from 2000 to 2020. Products of interest were searched using "meat analog\*", "meat substitutes", "alternative protein", "plant-based", "hybrid meat", "meat extenders", "meat replacement", and "extrusion". Consumer studies and sensory descriptive analysis methods were selected using "consumer liking", "consumer acceptance", "consumer perception", "sensory quality", "sensory characteristics", "sensory properties", and "descriptive sensory evaluation". Studies involving meat analogs made with insects, mycoproteins, algae, and in vitro meat as a protein source were removed. In the case of meat extenders, only studies evaluating products in which at least 30% of the protein content was replaced with plant proteins were selected. Studies with products containing functional ingredients as food additives but where animal protein was not replaced with plant proteins were excluded. While numerous studies on consumer perception of meat analogs were found, online surveys, questionnaires, and focus groups where data were collected based on visual or verbal information and not through tasting were excluded. Following an initial search, and secondary screening of the above criteria, the review resulted in the selection of 14 articles.

#### **3. Literature Review**

Fourteen research papers were found within the defined search query. These are summarized in Table 2. Of the 14 selected papers, 11 evaluated consumer acceptance with hedonic testing and 3 used sensory descriptive analysis. Eleven evaluated 100% plant-based meat analogs, and 3 evaluated extended meat products. Twelve evaluated the addition of ingredients and 2 evaluating processing/cooking methods. The main protein source was soy in the form of isolate, concentrate, or flour, followed by wheat gluten and peanut. All meat analogs were prepared by either extrusion processed, emulsified systems (e.g., sausage) or formed materials (e.g., nuggets, meatballs, patties). Samples were cooked in different methods (e.g., oven-baked, pan-fried) with or without seasonings or marinades, depending on what type of processed meat the product was meant to recreate. During sensory evaluation, the control samples consisted of either a commercial meat analog or a meat equivalent product. For studies testing the most adequate concentration of functional ingredients, the control sample was the one where the ingredient of interest was not added. Table 3 summarizes the reviewed articles, which are categorized by the sensory attribute of interest, by highlighting the strategies that have been tested, the type of control used, and the main finding. Table 2 shows a summary of articles employing consumer and descriptive analysis tests.



DPF: defatted peanut flour; PPC: peanut protein concentrate; PPI: pea protein isolate; SF: soy flour; SPC: soy protein concentrate; SPI: soy protein isolate; TSP: textured soy protein; TVP: textured soy protein; WG: wheat gluten; WP: wheat protein.


**Table 3.**Summary of findings for reviewed articles.

#### *Foods***2020**, *9*, 1334

#### *3.1. Color and Overall Appearance*

The overall appearance of a product is important for priming consumers and developing expectations prior to consumption. A disconfirmation of expectations occurs when the perceived liking after consumption is below the expected liking, which may occur when the visual cues misrepresent the taste, odor, and flavor of the product [39]. Thus, it is important to deliver high-quality sensory attributes that are perceived both before and during consumption. The overall appearance of meat analogs should resemble familiar meat products in order to set positive expectations. A combination of cooking parameters, such as time and temperature, have been tested to improve the overall appearance of meat analogs as they can impact the final visual appearance of the cooked product. Gomez and colleagues [28] tested the effect of changing cooking time and temperature on the color attributes of a ready-to-eat soy meat analog using the *sous vide* technique, which consists of cooking a vacuum-sealed product at low temperatures in a water bath. Both the meat analog and a beef equivalent were treated with two marinades, beer and teriyaki, and cooked at varying times and temperatures. The main ingredient in teriyaki marinade was pineapple juice (71%) resulting in a light-yellow color, whereas the beer marinade was made with pale lager beer (80%), resulting in a more golden color. A hedonic test was performed by 73 consumers who rated three visual parameters of the product. No significant difference in hedonic scores was detected between the samples, suggesting that the meat analogs were equally accepted as the beef samples in terms of visual appearance. In addition, results from color analysis revealed that both samples cooked with similar parameters had the same values for lightness and redness, which is the characteristic color parameter for meat products, suggesting that this cooking technique can be used to develop meat analogs with a similar appearance as their meat equivalent, regardless of the type of marinade used. Instrumental color analysis also revealed higher yellowness values in the samples cooked with teriyaki marinade compared to the beer marinade. This was attributed to the lighter yellow color of the teriyaki marinade. These results can be used to direct product development of meat analogs in terms of color depending on the desired outcome.

Certain ingredients can affect the color and appearance of meat analogs. Sharima-Abdullah and colleagues [29] developed meatless nuggets by changing the ratio of chickpea flour to texturized vegetable protein. Hedonic test showed that color and appearance scores increased as chickpea flour concentration increased. These results were explained by the presence of carotenoids in chickpea contributing to a yellow color, which was appealing to the participants. Surprisingly, increasing hedonic scores for color did not correlate with increasing overall acceptance scores. In fact, overall acceptance seemed to decrease as the percentage of chickpea flour increased. A 10:30 ratio chickpea flour to textured vegetable protein (TVP) resulted in the highest acceptance scores. This was explained by an increase in dislike of the nuggets in terms of taste. This provides evidence that multiple sensory attributes play an important role in consumer acceptance.

One processing limitation of using plant proteins is that the color of meat analogs may fade out when exposed to light or oxygen, leading to an unappetizing product [40]. Marinating can be used as a preparation method to change the color of meat analogs prior to cooking. Other ingredients used in the formulation of meat analogs can dictate the color of the final product. Teriyaki and/or beer marinades as well as chickpea flour are acceptable ingredients to obtain a bright yellow color that is appealing to consumers. Cooking parameters such as time and temperature can also affect the appearance of meat analogs. A higher moisture content in a meat analog cooked at high temperatures can lead to deeper penetration of light in the product, resulting in a brighter color. These studies demonstrate that several approaches can impact consumer ratings for the color and visual appearance of meat analogs.

#### *3.2. Taste, Flavor, Aroma*

A common disadvantage of using plant proteins in meat analogs is the generation of volatile compounds from the lipid oxidation of unsaturated fatty acids that contribute to the formation of unappealing odors and flavors [41]. To overcome this problem, food scientists develop recipes that include flavoring mixtures with seasonings, spices, and enhancers that can both replicate the typical flavor of smoked meat as well as mask the beany, grassy, or green aroma of pulses. To assess consumer acceptability of meat analogs in terms of taste, flavor, and aroma, the sample is presented in a way so that it resembles the equivalent meat product. In a study performed by Rehrah et al. [30], three formulations of peanut-based minced product were evaluated against a commercial soy-based minced product in a seasoned puff pastry application. The peanut-based meat analog was made by fortifying defatted peanut flour with peanut protein concentrate. The mixture was extruded, ground into a beef-like mince, and stuffed into a rolled puff pastry to provide a more realistic version of a commercial snack. All three formulations of textured peanut protein concentrate (PPC) were seasoned with beef flavor and soy sauce as a flavor enhancer. In addition, the first sample contained tomato powder, the second sample contained crushed red pepper, and the third sample had no modifications. A sensory panel of 60 participants rated the peanut-based sample along with the commercial soy-based control in terms of beefy flavor, off-flavor, and spiciness on a 9-point hedonic scale. Participants were also asked to determine spiciness on a just-right scale with three intensities (too little, just right, too much). Of the three formulations of peanut-based meat analog, the one containing crushed red peppers had the most acceptable meaty flavor, the least dislike of off-flavor, and the most adequate spiciness level. These results suggest that the addition of flavors, enhancers, and spices can positively affect consumer acceptance of taste of a meat analog. However, while PPC performed better than soy-based formulations in a puff pastry application, the study did not include comparisons against a traditional meat formulation, suggesting that the choice of the control is a significant variable to be considered. On one hand, if the reference and test samples consist of different plant proteins, hedonic responses may be affected by the additional spices, with the most seasoned formulation resulting in higher acceptance scores. Alternatively, using a full-meat sample as a control would help to best determine how a meat analog compares to the desirable sensory properties of a traditional animal product.

Comparing plant-based meat analogs to their meat equivalent can be adopted as a strategy during evaluation of extended meat products. Wong and colleagues [31] developed three formulations of hybrid beef patties by substituting 10%, 20%, and 30% ground beef with hydrated textured soy protein (TSP). A first hedonic test with 55 consumers showed no significant difference in overall liking scores for all formulations compared to the all-beef control. In a second hedonic test, 56 consumers evaluated the sensory properties of a hybrid beef patty with 20% TSP substitution and all-beef patty both with reduced sodium level. Liking scores for flavor were slightly lower in both the 20% TSP patty and the all-beef patty with reduced sodium compared to the all-beef control with regular sodium level. This suggests that substitution of beef with plant protein up to 30% can lead to acceptable liking scores as long as the sodium content remains unchanged. These findings reveal that maintaining a high sodium level in meat analogs is important for consumer acceptance in terms of flavor, although this may lower the nutritional quality of the final product. In another study, Grasso et al. [37] developed four types of hybrid meatballs by substituting 15% and 30% of beef with TSP in duplicates, with or without nutritional yeast, which was used as a flavor enhancer for its strong umami flavor. Sixty participants evaluated the four samples and an all-beef control by assessing degree of liking on a 9-point scale in terms of flavor, texture, and overall acceptance. In addition, participant used the check-all-that-apply (CATA) method by selecting the most appropriate terms to describe the samples. This method provides a complete description of the sensory characteristics of the samples. A list of 24 terms was chosen from the available literature on meat products. The CATA terms related to flavor were "tasty", "bland", "cheesy", "weak meaty", "strong meaty", "wheat-cereal like", "unusual", and "characteristic". Results from the hedonic test showed that addition of 15% TSP and nutritional yeast resulted in the highest liking scores for flavor and overall acceptance. Results from CATA analysis revealed that this sample was most associated with the term "tasty" and less associated with "bland", while the 30% TSP without yeast was most associated with "wheat-cereal like", suggesting that the absence of flavor enhancers in a sample with a high percentage of soy content may lead to the detection of strong off-flavors. Interestingly, the all-beef control was most frequently associated with the term "bland". This suggests that the selection of control is important in understanding and interpreting consumer

acceptance of hybrid products. It is important to select a control that is liked by consumers and is a good representation of the target product, as a low-quality control product could lead to misinterpreting results. Partial replacement of animal protein with plant protein provides the opportunity to improve the sustainability of meat products while also improving the nutritional profile of processed meat. However, addition of plant proteins might affect the overall product quality. The addition of up to 15% vegetable protein is appropriate to improve healthfulness of meat products without reducing the quality of sensory attributes.

When the objective of the study is to test how different concentrations of a flavoring agent affect the sensory attributes of the final product, the sample without the added ingredient is used as a control, as opposed to using a full-meat product or a commercial meat substitute. Chiang et al. [32] added Maillard-reacted beef bone hydrolysate (MRP) at four concentrations to a meat analog made with soy protein concentrate and wheat gluten to improve its sensory attributes. Beef-bone extract, a by-product of meat processing, can be used as a flavor-enhancing agent by undergoing enzymatic hydrolysis to increase the proportion of free amino acids, followed by Maillard reaction through addition of reducing sugars to produce heterocyclic compounds. These molecules contribute to the typical flavor and aroma of smoked meat when this is cooked on the grill. Sensory evaluation by a group of 55 consumers revealed that 20% MRP was the optimal level for acceptance, resulting in the highest sensory scores for meaty aroma and meaty taste. By contrast, addition of 40% MRP received the lowest scores in all attributes due to bitter taste and a burnt appearance, while 0% MRP (the control) resulted in a weaker meaty taste and an undesirable pale brown color. The addition of MRP, under a certain concentration, helps to increase desirable "meat" flavors and increases acceptance compared to unflavored meat analog. It is not known if the addition of MRP would compare to a full-meat control. However, this product includes meat extracts, making it inappropriate for vegans and vegetarians; yet, it demonstrates the use of hydrolyzed protein materials can enhance desirable flavor attributes, which is important in increasing overall acceptance of meat analogs.

Katayama and Wilson [25] used a similar approach in their study. The aim was to determine the most acceptable concentration of vegetable-based "chicken" and "shrimp" flavors added to textured soy meat analogs prepared in four different shapes (narrow strip, wide strip, shred, and bit) and with two cooking methods (fried and baked). The use of vegetable-based flavors provides an acceptable alternative to meat-by products like beef-bone extract, which may represent a barrier for vegan consumers. In the study, "chicken" flavor was added in either powder or liquid form at 3% and 4% to all four shapes of extrudates, which were fried, while two types of "shrimp" flavor, one oyster-like, the other a combination of oyster and crab-like, were added to shred-shaped extrudates, which were baked. A trained sensory panel of 14 participants generated a list of descriptive terms based on chicken and shrimp flavors to evaluate the samples. All formulations were rated on an analog scale using unflavored samples as controls. Results showed that the presence of 4% flavoring enhanced the overall saltiness and meatiness. The size of the product sample appeared to significantly impact the "chicken" flavor in powder form as the narrow strip-shape was more intense in the oily flavor compared to the wide strip sample. This was attributed to the formation of air pockets in the former, responsible for encapsulating flavor molecules during frying. Following descriptive analysis, researchers conducted a consumer preference test with 125 volunteers for evaluating the "chicken" flavored product. Consumer results revealed that the chicken-flavored sample was most accepted when fried rather than baked. However, chemical analysis showed that the fried samples had more than 3 times higher fat content than the baked samples, suggesting that the higher fat content may increase liking. Moreover, this cooking method can negatively impact the nutritional quality of the product. In this study, researchers first used a descriptive sensory analysis to determine the best product formulation based on variables, such as type and concentration of the flavoring agent as well as shape and cooking method of the sample. Then, a consumer preference test was performed to evaluate the product based on a single variable. Performing a consumer test following descriptive analysis is a common strategy to efficiently assess consumer acceptance by combining both quantitative and qualitative data on the sensory profile

of meat analogs in order to collect more specific information that can be used to apply changes in the recipe or processing method.

The formation of unappealing odors and flavors during processing of plant proteins represents a barrier to acceptance of meat analogs. Addition of spices, seasonings, and flavor enhancers is an appropriate strategy to mask the beany and grassy aroma, specifically in pulses. The nature of the added ingredient may need to comply with vegetarian and/or vegan consumers' dietary restrictions. Meat by-products such as beef bone hydrolysate can provide a "meaty" flavor to meat analogs in order to increase acceptance among non-vegetarian consumers. Yet, vegetable-based mixtures have been successful in recreating the flavor of poultry or seafood products. Use of spices, such as red pepper flakes, can increase spiciness to overcome off-flavors, while nutritional yeast can be used as an enhancer to provide a "meaty" umami taste. Sensory evaluation methods aimed at identifying acceptable flavoring ingredients can be influenced by the selection of the control product. Comparing two different kinds of plant proteins as opposed to using a full-meat control can impact conclusions drawn regarding product liking. Further research should focus on evaluating the taste and flavor of meat analogs in a meal context, as additional foods in the dish can alter the perception of oral sensation of meat analogs.

#### *3.3. Texture*

Another challenge for meat analogs is the recreation of the unique texture, mouthfeel, and juiciness of traditional meat products [41]. For meat analogs, the focus has been on the selection of plant protein to recreate the physiochemical properties of animal protein. Factors include the ability to encapsulate fat, their oil- and water- holding capacity, and gelling and emulsifying properties, which can be measured through texture analysis. Instrumentation combined with sensory evaluation, such as consumer liking, can be a helpful indicator of consumer acceptance for texture.

Choosing the right protein source is essential to develop vegetarian versions of meat products. Gluten is the main protein source in wheat, and it is commonly added to processed meats as a binding agent for its viscoelastic properties that allow to form a cohesive network in the product. Kamani and colleagues [38] used soy protein isolate and wheat gluten to develop two products, (1) a meat-free sausage and (2) a reduced-meat sausage containing only 20% of chicken. Results from the hedonic test showed no significant differences in the liking texture scores between samples containing both 80% and 100% plant proteins compared to the full-meat control. This was associated with texture analysis data, showing a reduced cooking loss and a better emulsion stability in the samples with partial and total replacement of meat. Implementing the results from sensory evaluation, which is subjective, with instrumental results from texture analysis allows to either confirm the outcome of the study or identify possible inconsistencies in the methods. However, it should be noted that Kamani and colleagues [38] collected hedonic responses using a trained panel, which goes against the standard procedure of sensory evaluation method for consumer acceptability. Thus, these results should be analyzed with caution due to methodological issues and represent a limitation of the study.

In addition to the selection of plant protein source, another way to improve the texture of meat analogs is by using food additives. Hydrocolloids have gelling, thickening, emulsifying, and stabilizing properties due to their ability to interact with water, proteins, starch, and other components in the food product. The meat industry often incorporates hydrocolloids in meat sausages to compensate for textural quality loss that occurs when part of the fat and salt is reduced. Common types of hydrocolloids for meat analogs include carrageenan, an algae-derived polysaccharide, xanthan gum, a polysaccharide produced by bacterial fermentation, and konjac mannan, a tuber-derived heteropolysaccharide. Majzoobi and colleagues [33] found that addition of either 0.3–0.6% kappa-carrageen or 0.6% konjac mannan resulted in the highest consumer acceptability scores of a soy protein isolate (SPI) sausage. These results were confirmed by textural analysis showing that sausages produced by k-carrageenan and konjac mannan had the highest water-holding capacity, leading to the production of a strong network within the sausage matrix and an increase in tenderness of the samples. Similarly, Palanisamy et al. [34]

found an improvement in textural attributes of a soy meat analog by increasing the concentration of iota-carrageenan (ICGN), with 1.5% being the optimal level for hedonic texture ratings. However, results showed that all test samples had poor overall acceptability, including the 0% ICGN control sample, as no samples included seasonings or spices, which was intentional to avoid any influence on the perception of texture. In this instance, while texture was improved, creating a desirable texture alone is not sufficient to create an overall suitable product. It is important to consider how sensory attributes together influence consumer acceptance. Moreover, it should be noted that the consumer group used in this study is small, making it inappropriate to generalize the hedonic responses regarding the product sample.

Other functional ingredients that are used as food additives to improve the texture of meat analogs include thickeners and emulsifiers. Bleached tomato pomace, a by-product of tomato processing, is rich in fiber and pectin and is used as a thickening agent. Savadkoohi et al. [35] developed three sausage formulations, namely soy, beef, and ham, which were evaluated by a descriptive sensory analysis based on the added concentration of bleached tomato pomace. Three commercial samples with no tomato paste addition were used as controls. Thirty consumers rated the liking of sensory properties on a line scale for each sample. Sensory scores showed that addition of bleached tomato pomace at 5% was the optimal level for acceptance. This was confirmed by instrumental textural analysis showing that addition of tomato pomace increased textural hardness and chewiness of the meat analog. However, analysis revealed that additive concentration greater than 5% resulted in an undesirable orange-green color compared to the control. In another study, Wi et al. [26] added non-animal-based liquid additives, including water, hydrated SPI, canola oil, and lecithin to an emulsified meat analog made with TVP and SPI. Sensory evaluation was performed by 10 panelists who rated the intensity of firmness, elasticity, stickiness, compactness, roughness, soy taste, oil taste, juiciness, and overall acceptance on a 7-point scale. Results showed that juiciness was positively affected by water treatment, whereas overall acceptance was positively correlated with emulsion treatment.

Finally, the processing methods can influence texture and mouthfeel properties of meat analogs. Lin et al. [27] tested the effects of different moisture content and cooking temperature on the attributes of an extruded meat analog made with soy protein isolate. For sensory data, a trained panel of 9 judges evaluated the samples based on 7 descriptive terms related to mouthfeel. The authors combined data from sensory evaluation and instrumental analysis, including texture profile analysis, water absorption capability, and microstructure, which was determined by scanning electron microscopy. They found that changes in moisture content had a greater effect on sensory and physiochemical properties than cooking temperature. However, while results showed a correlation between directional structure and textural attributes like hardness or chewiness, the study did not determine whether this affected consumer acceptance. In another study, Yuliarti et al. [36] developed plant-based nuggets using a freeze structuring technique, which consists in the freezing of a protein emulsion to generate a unique fibrous structure and a subsequent removal of ice crystals to generate a porous and fibrous microstructure, similar to that of animal meat. Five formulations of nuggets were developed by changing the ratio of pea protein to wheat protein. Two of the five samples were used as controls, namely 17:0 and 0:17 pea protein isolate (PPI) to wheat protein (WP). A hedonic test was conducted with 42 untrained participants who rated the analog in terms of texture on a 5-point acceptance scale. Results showed that freeze structuring technique was able to form a fibrous and layered structure of the plant-based protein nuggets, however, this technique was also dependent on the type of protein used. In fact, a 4:13 PPI to WP ratio was the most preferred analog compared to controls. Microstructure of this analog indicated fibrous and layered structure, while textural profile analysis was found to be related to the viscoelastic properties of WP and was strongly affected by the extent of cross-linking between protein molecules. A combination of hedonic tests, descriptive analysis, and analytical methods is ideal to explain the impact of processing parameters on texture and mouthfeel attributes.

The structure of muscle meat is challenging to recreate without the use of animal proteins. The selection of plant proteins with viscoelastic properties like wheat gluten can help to improve

the texture and mouthfeel of the final product. In addition, ingredients like hydrocolloids, gels, and gums can be used for their emulsifying properties. Optimizing synergistic effects of different ingredient ratios can further advance texture quality perception. Extrusion parameters can be modified to obtain a desired texture, with changes in moisture content playing a greater role in physiochemical properties than cooking temperature. Freeze structuring technique can generate a fibrous and layered structure in plant-based nuggets. This strategy can be adopted when extrusion cooking is not available. Future sensory evaluation studies should explore how the texture of meat analogs is affected by other components in the meal with different consistencies, such as sauces and soups, which can alter the perception of oral sensations of meat analogs. Moreover, the application of commercial ingredients that utilize the synergistic effects of soy and gluten should be further investigated to optimize the creation of desirable textural properties of meat analogs.

#### **4. Conclusions**

This review focused on research papers evaluating the impact of ingredients and processing methods for meat analogs and meat extenders on sensory attributes and consumer acceptance. This area of research helps provide important information on the use of novel plant proteins in meat analogs, as they are known to have processing limitations. The color of plant-based products may fade out due to light or oxygen exposure, leading to an unappetizing appearance. An undesirable taste can occur due to off-flavors from lipid oxidation of unsaturated fatty acids in plant protein ingredients and products. Texture attributes such as fibrous structure, tenderness, and juiciness of muscle protein are very challenging to recreate in plant proteins due to the reduced saturated fat content. Current research in food science is investigating strategies to improve the overall quality of meat analogs. In terms of increasing consumer acceptance, studies have focused on adjusting formulations and cooking methods to improve color, flavor, and texture of meat analogs. In this regard, it should be noted that the choice of protein source is an important factor to be considered in the development of meat analogs as it can influence the perceived sensory attributes of the finished product. For instance, leguminous proteins such as soy and pea, while high in protein content, have some processing limitations leading to the production of strong off-flavors. Peanut protein has some processing advantages as it is very nutrient dense due to the high protein, fat, and fiber content. Moreover, peanut protein was found to perform better than soy in a puff pastry application in this review. Wheat gluten can be used for its viscoelastic properties to improve the texture of meat analogs, however, it has a much lower protein content than soy and peanut. Finally, soy, peanut, and wheat are three major food allergens, suggesting that the application of any of these ingredients may lower consumer acceptability of meat analogs depending on the consumer.

Sensory evaluation methods, involving untrained or trained consumers, can provide a better understanding of how different factors, such as processing and ingredients, affect quality attributes and overall consumer acceptance of meat analogs. Studies that employed more than one sensory method were able to identify the combination of parameters or ingredients that resulted in the highest acceptance scores for the sensory attribute of interest. Studies that used a qualitative approach to evaluate the samples were useful to identify the magnitude in which sensory attributes were influenced by test parameters. However, using this approach alone reduced the ability to understand the potential to impact or improve consumer acceptance values. A combination of hedonic testing and descriptive analysis provides a more holistic understanding and an ideal approach to evaluate the sensory profile of meat analogs while also being able to identify the strategies to increase consumer acceptance of these novel foods. Moreover, it is important to follow standardized procedures when choosing the appropriate sensory evaluation method, as these might compromise the reliability of scientific results. Factors such as the number of participants and training can influence the sensory scores and lead to inaccurate interpretation.

Sensory characteristics, including color, flavor, and mouthfeel of meat analogs can be modified through addition of functional ingredients and selection of processing methods. For color parameters, marinades, or other ingredients containing yellow pigments can be used to improve the overall appearance of the final product. Different flavoring agents and seasonings can either mask the undesirable odors of plant proteins or recreate the umami and "meaty" flavor. Texture can be adjusted to resemble muscle structure through the application of plant proteins as independent materials and as blends, with or without the addition of hydrocolloids to change the viscosity. Extrusion cooking or freeze structuring technique results in desirable fibrous structures. Sensory data is a key component in understanding the physiochemical characteristics of novel plant proteins to increase consumer acceptance of meat analogs in order to make a significant advancement in more sustainable and healthy foods.

**Author Contributions:** Conception of the review and identification of the literature, M.F. and A.A.N.; drafting of manuscript and tables M.F.; critical revision and intellectual content, M.F., A.J.K., and A.A.N; supervision, A.A.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

### *Review* **Plant-Based Cheeses: A Systematic Review of Sensory Evaluation Studies and Strategies to Increase Consumer Acceptance**

**Erin C. Short, Amanda J. Kinchla and Alissa A. Nolden \***

Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA; ecshort@umass.edu (E.C.S.); amanda.kinchla@foodsci.umass.edu (A.J.K.)

**\*** Correspondence: anolden@umass.edu

**Abstract:** Animal protein provides unique sensory and textural properties to foods that are not easily replicated when replaced with plant-based alternatives. Food scientists and researchers are currently developing innovative approaches to improve their physical and sensory characteristics in plant-based analogs. In terms of plant-based cheese substitutes (PBCS), soy is the most commonly used plant-based protein but is associated with undesirable sensory attributes (i.e., beany and gritty). In order to determine if the approaches result in a significant improvement in sensory quality and liking, sensory evaluation is employed. The aim of this review is to summarize the original literature (*n* = 12) relating to 100% PBCS which utilizes sensory evaluation methods. Overall, a major theme identified in this review is the innovative strategies used to increase acceptance of PBCS, whether products are aimed at improving existing non-dairy-based cheese formulations or to more closely mimic a conventional dairy-based cheese product. Studies demonstrate processing and fermentation of soybeans and blending of non-dairy milks are potential ways to improve consumer liking of PBCS. A secondary focus is to discuss the current sensory methodology carried out in the reviewed literature. Future studies should consider using more specific measures of flavor and mouthfeel, integrate evaluation of consumer liking with instrumental textural methods, and use a larger more diverse group of consumers. The outcome of this review is to highlight the importance of integrating sensory science in order to help facilitate the improvement of the sensory and quality attributes of PBCS and streamline product development.

**Keywords:** non-dairy cheese; soy-based cheese; sensory evaluation; consumer acceptance

#### **1. Introduction**

Augmented interest in plant-based foods has increased due to concerns related to health, sustainability, and animal welfare. In terms of conventional production of dairy, there are three major areas of concern: environment impact (emissions of greenhouse gases, pollution of soil and water, and land use), human health (exposure to zoonotic diseases and increased antibiotic resistance), and animal welfare (treatment of farmed animals, including disease, injury, and mental/emotional well-being) [1]. Therefore, plant-based products offer a more sustainable and ethical option to consumers that are rapidly increasing in popularity among consumers. As a testament to this, U.S. retail sales of plant-based substitutes that directly replace animal products grew 29% between 2017 and 2019 to reach a USD 5 billion market. In the dairy category plant-based cheese substitutes (PBCS) saw the most growth in a year-over-year retail sales comparison by increasing 95% in 2020 [2,3]. Within the plant-based product market, PBCS is an emerging segment that has yet to gain traction or interest from a diverse consumer base [4]. Although PBCS sales continue to grow, the category remains in its infancy compared to other plant-based analog categories (i.e., dairy and meat) [5,6] as PBCS only accounts for less than 1% of all total dollar sales of retail cheese [3]. In order to increase acceptance of these products, sensory methods can be

**Citation:** Short, E.C.; Kinchla, A.J.; Nolden, A.A. Plant-Based Cheeses: A Systematic Review of Sensory Evaluation Studies and Strategies to Increase Consumer Acceptance. *Foods* **2021**, *10*, 725. https://doi.org/ 10.3390/foods10040725

Academic Editor: Antti Knaapila

Received: 5 March 2021 Accepted: 27 March 2021 Published: 30 March 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

employed to better understand sensory and quality attributes and whether they provide the desirable qualities of a conventional dairy-based product.

Consumer liking is arguably the biggest challenge for any plant-based substitute. From a US consumer standpoint, only 32% agree that PBCS taste as good as regular cheese, while 34% disagree, and another third of cheese consumers remain indifferent [4]. If the PBCS express quality attributes that meet consumers' expectations, then these substitutes can be a satisfactory replacement for a dairy counterpart [4]. The Food and Health Survey consistently shows that taste is the number one driver behind purchase intention [7], more important than price, convenience, and health. Therefore, it is important to develop a product that provides desirable sensory characteristics (i.e., taste, flavor, and mouthfeel properties). In summary, the low sales margins indicate that the consumer market is left unsatisfied and there is substantial room for improvement and growth within this product category.

For PBCS, there are two general approaches to the flavor profile: (1) those which intend to mimic the sensory attributes of conventional dairy cheese and (2) those that embrace the unique flavors and characteristics derived from the plant. The challenge with the former is that plant-based ingredients do not precisely mimic the sensory (i.e., flavor, taste, and aroma) and physical (i.e., mouthfeel and meltability) characteristics of dairy-based cheese which limits consumer acceptability. Yet, the latter expresses novel characteristics in products that may not be desirable to the majority of consumers which has resulted in a specific and narrow niche market. Regardless, if the goal is to mimic or embrace the sensory characteristics, the end product should have physical, functional, and sensory properties that consumers find desirable [8]. To achieve this, sensory evaluation, specifically hedonic evaluation, must be employed to assess the product performance.

Among the accessible published literature of PBCS, the focus has been on soy-based "spreadable" products. This work is not representative of the diverse ingredients used in PBCS products displayed on grocery store shelves. Between 2015 and 2020 coconut oil was the top ingredient in new PBCS, with other common ingredients dominating the retail market include modified and native starches and nut milks [9,10], while available research tends to focus on soft "spreadable" soy-based products. Soymilk's functional and nutritionally complete proteins [11] are comparable to cow's milk and the availability and affordability of soy [6] are some reasons why researchers tend to focus more on this dairy alternative. One potential limitation of soybeans are the concerns with high estrogen levels [12] and being a common food allergen. Relying on plant-based ingredients to simulate the processed nuance of dairy cheese, including the physical, chemical, and functionality properties, is no easy task and sensory challenges are inevitable. Like any plant-based ingredient, soybeans in particular exhibit flavor and mouthfeel challenges, specifically, beany flavor and gritty mouthfeel [6].

To the authors' knowledge, there has not been a review of the sensory attributes of PBCS. This systematic review focuses on the studies that have conducted sensory evaluation of PBCS. After performing the search, (see Methods below), it became clear that all but one of the studies focused on soy-based products and applied different processing techniques, approaches, or methods to improve consumer liking. As a result, the goal of this review is to summarize the literature aimed at improving consumer liking of soy-based PBCS. This review is organized by first summarizing the breadth of work published that aims to improve the sensory attributes and describe the results of the consumer sensory evaluation. We then summarize the current limitations within the existing literature in terms of the sensory evaluation methodology and suggest several areas of needed exploration that have yet to be examined (i.e., consumer segmentation and alternative plant-based proteins). There is an opportunity to improve the PBCS market by decreasing undesirable sensory characteristics and improving overall liking. In order to achieve this, sensory science should complement ongoing scientific research regarding PBCS in order to directly improve the quality and sensory attributes and lead to more efficient development processes.

#### **2. Methods and Search Criteria**

A systematic search was carried out using the Web of Science and Google Scholar on studies published in English through March 2021. The search used keywords pertaining to plant-based and imitation cheeses and included sensory evaluation. The following keywords included: "cheese analog(ue)s", "cheese substitutes", "imitation cheese", "cheese replacement", "alternative cheese", "non-dairy cheese", "cheese-like" and "plant-based cheese." Consumer studies coupled with other sensory evaluation analytical methods were selected using "consumer liking", "consumer acceptance", "consumer perception", "sensory quality", "sensory characteristics", "sensory properties", "sensory evaluation". The initial search identified 33 articles. We excluded online focus groups, surveys, and questionnaires, where data was collected based on verbal or visual information and not through sampling products (*n* = 8 articles). Following an initial search and secondary screening of the above criteria, the search resulted in the selection of 25 articles.

Within the plant-based literature, the term "analogue" is reserved for plant-based products that simulate properties of the conventional animal-based product [13]. While this established term indicates no animal-derived ingredients, within PBCS literature "analogue" is interchangeable for both 100% plant-based and products made with partial dairy ingredients [14,15]. This dual use of the term "analogue" in regard to PBCS has led to confusion within the scientific community. This review focuses on cheese analogs made without any dairy ingredients and studies involving 100% plant-based ingredients. Of the 25 articles found within our defined search query, we excluded 13 papers that evaluated cheese analogs made partially with dairy. Of the remaining 12 articles which evaluated 100% plant-based cheese: 10 PBCS were soft, spreadable products while 2 focused on hard or semi-hard cheeses; 5 were made with only soy and 6 evaluated blended ratios of soy and nut milks; 1 evaluated commercially available coconut-based cheese (Table 1). Only one study purchased commercially purchased products, all other studies created the product for the purpose of the study. Three studies included a conventional dairy-based product as a control [10,16,17]. All studies included a measure of acceptance or liking while four studies [10,16,18,19]. performed a combination of descriptive and hedonic evaluations (Table 1). It was also noted that several studies had limitations in their methodology for sensory testing, which are common errors, such as small participant pools, choice of control, and usage of trained panelists (described below in Section 4).


**Table 1.** Overview of PBCS articles employing sensory analysis.

H/D: hedonic and descriptive sensory methods; Ferm: fermentation; BM: blending milks; B\*: blended carrot puree; SB: sodium bicarbonate; N/A: Compared commercially available products, Commercial ProductsA: One study compared attributes across commercially available products.

#### **3. Literature Review**

The sensory challenges for developing soy-based PBCS products have been most often attributed to undesirable beany flavor and gritty mouthfeel [6,16,27]. The beany flavor from soybeans occurs as a result of lipoxygenase activity [27], which does not occur in undamaged raw soybeans; however, in the presence of water and oxygen, an enzymatic process takes place and emphasizes off-flavors [28]. The gritty mouthfeel is a result of the larger, rough particulates, made up of proteinaceous, carbohydrate, and cellulosic components [29]. These attributes are often considered to be "off characteristics" which diminish the overall quality and acceptance of the soy-PBCS while their dairy counterparts remain smooth and uniform [16]. Adapting various soybean processing methods (i.e., posed solutions of fermenting, blending milks, blanching, and/or adding sodium bicarbonate) report a refinement in sensory characteristics which is necessary in order to increase overall liking.

One study completed a sensory profile of commercially available plant-based cheese and compared their acceptance to a conventional dairy-based cheese product. The remaining literature (*n* = 11) focuses on evaluating processing strategies to improve the liking and sensory qualities of PBCS (refer to Table 1). These strategies can be divided into three categories (1) modified fermentation (*n* = 3), (2) blending milks (*n* = 4), and (3) modified processing (*n* = 4) of soybeans. Here, we summarize the results of these strategies in terms of improving their liking using sensory evaluation methods, all of which suggest an improvement in sensory profile resulting in increased liking of PBCS.

#### *3.1. Strategies to Improve Consumer Liking*

#### 3.1.1. Modified Fermentation

In order to prevent a gritty mouthfeel (sedimentation of large particles) and ultimately obtain a soy-PBCS with a smooth texture, alternate methods include the adoption of fermentation techniques. Specifically, the incorporation of lactic acid bacteria (LAB) softens the rough particulates in order to achieve a smoother texture when blended [30]. The role of soymilk fermentation is suggested to aid in removing the undesirable beany flavor while inadvertently improving the nutritional composition [16]. An additional method of incorporating sodium bicarbonate increases the pH which affects the protein structures of the soybean seed coats and allows for the reduction of the gritty mouthfeel [31]. The following studies incorporated combination approaches of sodium bicarbonate and various fermentation techniques were suggested to improve the beany and gritty characteristics expressed by soybeans, although no study specifically measured these characteristics.

Two studies Li, Q. et al. [16] and Li, Y. et al. [18] coupled both hedonic and descriptive testing methods to evaluate whether modified fermentation improved the sensory attributes and acceptance PBCS. Li, Y. et al. [18] initially soaked the soybeans in a 0.5% (wt/vol) sodium carbonate solution for 20 min before creating the soymilk. The milk was then inoculated with 3% of the LAB starter culture and/or *Geotrichum candidum* at 10<sup>4</sup> CFU/mL before undergoing fermentation. The control PBCS sample prepared with the LAB starter culture (which was not inoculated with *G. candidum*) was stored at 4 ◦C and used to compare maturation differences between the samples prepared with the combination of LAB and *G. candidum*. The samples were ripened in a variety of temperatures (4 ◦C, 10 ◦C, and 15 ◦C) and assessed at three different aging durations (21, 28 and 35 days). In the hedonic test, 10 trained panelists rated liking using a 5-point scale (0 = inconsumable, 1 = unacceptable, 2 = acceptable, 3 = satisfactory, and 4 = excellent). The panelists indicated that the highest-rated PBCS in terms of color, flavor, appearance, and overall liking was the sample which combined the LAB and *G*. *candidum* approaches (ripened at 10 ◦C for 28 days). Panelist ratings fell within the "excellent" category, which was higher compared to the traditional LAB PBCS product, which ranked "satisfactory" in terms of color, flavor, appearance, and overall acceptability. Following the hedonic analysis, a descriptive test was performed with the same panelists using a 5-point intensity scale (1 = little to 5 = very much). Ratings were collected for hardness, springiness, and chewiness. In terms

of textural profile, the authors described the textural attributes to be improved in the combination approach describing the product to change from "brittle and hard" to "soft and sticky". The authors concluded that the combined approach exhibited a more stable, homogeneous structure, and presumably reduced the undesirable beany and gritty sensory properties, which ultimately increased the consumer likeability. It should be noted that the study did not ask panelists to rate the samples in terms of beany or gritty sensory attributes in order to determine whether this affected consumer acceptance. For this study, no formal statistics were reported for collected liking and intensity ratings. This study also performed objective measures of textural properties using a texture profile analyzer and measured the hardness, adhesiveness, springiness, cohesiveness, gumminess, chewiness, and resilience. While it can be advantageous to pair instrumental and sensory methodologies, in this case, no formal comparison was performed between instrumental and sensory data.

Using a similar approach as above, Li, Q. et al. [16] first soaked soybeans overnight in a 0.1% (*w*/*v*) sodium bicarbonate solution before undergoing different fermentation conditions which included LAB, glucono-delta-lactone coagulation, and/or enzymatic hydrolysis. Sensory analysis was used to identify which fermentation approach resulted in an increased consumer liking, and compared intensity ratings of appearance, color, creaminess, firmness, spread-ability, and flavor to a dairy-based control. Sensory characteristics were rated on a 9-point structured scale by 10 trained panelists. The results indicated that the highest-rated PBCS sample for all attributes was prepared using a combination of LAB and glucono-delta-lactone processes. This sample received an overall liking rating of 7.4 which was significantly different compared to other PBCS (only using one fermentation method), with ratings between 6.3 and 6.8. Although the dairy control ranked significantly higher in terms of overall liking, scoring a 7.7, the utilization of the combined fermentation methods made a significant improvement in the overall liking compared to PBCS products. The dairy-based control performed significantly better for every attribute, except for creaminess, which was not significantly different from PBCS prepared with combination of LAB and glucono-delta-lactone processes. Results of this study exemplify how a PBCS ranks in comparison to a conventional dairy cheese product and how incorporating a combined fermentation method can help improve the sensory characteristics of PBCS. Similarly, a texture profile analyzer was used to quantify textural properties (hardness, adhesiveness, springiness, cohesiveness, gumminess, chewiness, and resilience); however, these results were not compared to hedonic performance. Combining instrumental and sensory data can be useful to identify relationships between textural properties and consumer liking. Further, it is suggested that this approach increases liking as a result of reducing the perception of beany or gritty sensory attributes; however, these attributes were not directly measured in this study.

Chumchuere et al. [19] evaluated the physicochemical properties of a (fried vs. unfried) semi-hard soy PBCS which utilized a combined fermentation approach, inoculated with LAB and *Streptococcus thermophilus*, and was ripened at 4 ◦C for 7 days. A group of 14 participants used a linear scale to rate liking and intensity of sensory attributes in order to identify if frying improved the sensory characteristics and overall liking. Results of the hedonic test indicated that the fried sample received a significantly higher rating for overall liking (average rating 54.1) compared to the unfried sample (average rating 33.5). The participants rated the intensity of taste (acidity, salty, bitterness, and astringency), flavor (strong, cheesy, fermented, beany, rancid), texture (firmness and open texture), and color. There were significant differences between the unfried and fried PBCS for color, firmness, open texture, astringency, and all but one flavor attribute (strong, fermented, beany, and rancid). Sensations that were rated as more intense included color, firmness, open texture, and strong flavor, and reduced intensity ratings for astringency and fermented and beany flavor. This study was able to confirm that frying PBCS increases liking by reducing undesirable sensory attributes (astringency, beany and fermented flavor). Intensity ratings on quality and sensory attributes help to understand the change in characteristics as a result of modified processing, which led to an increased hedonic rating.

#### 3.1.2. Blending Milks

Blending different ratios of plant-based milks with soymilk results in an improved flavor profile compared to 100% soymilk PBCS. While no study specifically evaluated off-flavors or perception of beany flavor in any product, it is suggested that this attribute is reduced as a result of blending soymilk with alternative non-dairy milks. Adejuyitan et al. [20] created soft PBCS prepared using fermented soybeans prior to blending soy and coconut milks at 5 different ratios to combat the naturally beany flavor of soymilk. Using a 9-point hedonic scale, ratings from 10 untrained participants indicated that the highest-rated PBCS sample in terms of flavor, texture, taste, and mouthfeel, and overall acceptability was the 50:50 soy/coconut blend. This sample had an average overall acceptability rating of 7.3 compared to the 100% soy control, which was rated at 5.6, resulting in a significant difference between the two samples. This study shows that the combination of the two methodologies, fermentation and a blended ratio of plant-based milks, resulted in improved flavor, texture, and increased consumer liking.

Khodke et al. [21] created six soft PBCS at varying ratios of soy to groundnut (a legume crop formally known as peanut) milk in order to reduce the naturally occurring beany flavor of soymilk. Results of a hedonic evaluation (9-point hedonic scale) performed by 10 trained participants indicated the 90:10 soy/groundnut ratio received the highest acceptability rating compared to other ratio blends, including PBCS control, in terms of color, flavor, appearance, texture, and taste. When comparing the 90:10 blend to the PBCS control, flavor (7.8 vs. 6.3) and appearance (8.6 vs. 7) attributes saw the greatest improvement in ratings. The 90:10 blend received an average rating of 8.0 for overall acceptability while the control, 100% soy, rated 7.5. Statistical analysis was performed but was not structured in a way to evaluate whether the attributes were significantly different across sample categories. This comparison provides evidence that incorporating groundnut milk with soymilk can improve the flavor and texture which can help to increase overall acceptability.

Balogun et al. [22] created soft PBCS by blending soy and tiger nut milks prepared with six different ratios to combat the naturally beany flavor of soymilk. Using a 9-point hedonic scale, 20 untrained participants screened for PBCS product consumption indicated that the blended product prepared with 95:5 soy to tiger nut ratio received the highest ratings in terms of color, taste, texture, aroma, and overall acceptability. This blended PBCS had an average rating of 7.4 for overall acceptability where the 100% soy control had an average rating of 6.3. Statistical analysis revealed no significant difference between the 5% tiger nut blend and control PBCS. Significant differences were observed for liking of taste ratings between 5% tiger nut blend and control PBCS, with the blended product receiving significantly higher ratings (7.0 vs. 5.7, respectively). Even with a small percentage (5%) of soy milk replaced with nut milk, it is suggested to reduce the beaniness of soy which results in improved flavor, texture, and overall consumer liking. For this study, it was not determined whether beaniness was specifically reduced; however, it was observed to improve taste compared to a 100% soy PBCS. Even though the incorporation of tiger nut milk improved liking of taste, for this study, it did not translate to a significant increase in overall acceptability of PBCS.

Other than blending with nut milks, one study has provided evidence of blending soy with carrot puree to improve the liking of soy-based PBCS compared to a dairy control. Butool et al. [16] incorporated different ratios of carrot puree at 10% and 20% ratios in order to improve the appearance, flavor, texture, color, acceptance, and nutritional value of the soy-PBCS. Although off-flavors were not exclusively acknowledged by the authors, it was understood that soybeans naturally express beany flavors and that incorporating carrot puree within the PBCS may aid in masking these undesirable characteristics. The samples were compared to the customary dairy counterpart, 100% buffalo milk, which acted as the control, and all were prepared in a traditional curry dish. Participants included 5 trained and 15 semi-trained participants and were asked to rate each sample on a 9-point hedonic scale in terms of color, appearance, flavor, and overall liking. The sample with 20% carrot puree received the highest average rating of 8.4, compared to the dairy control

sample which had an average rating of 8.5. A full-soy control was also rated by participants, receiving an average overall acceptance rating of 7.1. The greatest increase in ratings was observed for flavor, 6.5 compared to 8.3 for the PBCS control and 20% puree PBCS, respectively. While no formal statistics were performed, the authors concluded that incorporating carrot puree can lead to improvement in sensory characteristics (color, appearance, flavor, mouthfeel, taste, and overall liking). This study provides preliminary evidence that the incorporation of carrot puree into a soy-PBCS is able to produce a product that is not different from a conventional animal cheese product when incorporated in a meal.

#### 3.1.3. Modified Processing of Soybeans

In order to eliminate the beany flavor, blanching and grinding soybeans at or above 80 ◦C has shown to reduce lipoxygenase activity in order to improve these sensory properties [16]. Additionally, incorporating sodium bicarbonate results in the softening of soybean seed coats [31] in order to reduce the gritty mouthfeel expressed [6]. In the following studies, the methods of sodium bicarbonate, blanching, or blending a variety of plant-based milks at different ratios were utilized in order to improve the sensory characteristics of soy-based PBCS. This section reviews studies that performed modified processing, which often entails blending soybeans with other non-dairy milks.

Kadbhane et al. [23] created a spreadable PBCS with soybeans that were blanched in 0.5% NaHCO<sup>3</sup> solution for 10 min prior to blending 5 different ratios of soy to coconut (90:10, 80:20, 70:30, 60:40 and 50:50). All samples were ripened at 4 ◦C, sampled at day 1, day 3, and day 6 of maturation. For this study, there was no 100% soymilk PBCS control sample, and instead the samples were compared against each other and the maturation days prior. Results of a composite scoring hedonic test, with an unknown amount of participants, indicating the most preferred maturation period fell at day 1. In terms of PBCS samples, the 50:50 sample received the highest ratings in terms of appearance, texture, color, flavor, and overall acceptability. Overall, the 90:10 ratio consistently was rated the lowest while the 50:50 blended ratio was rated the highest in every category and for every maturation day (1, 3, and 6). For this study, no statistical analysis was performed. Nonetheless, this provides preliminary evidence that blending soy and nut milks and sodium bicarbonate could help to improve the likeability of PBCS.

James and colleagues [24] created 3 soft soy PBCS samples using different coagulants (lime juice, alum, and steep water) to further understand the physicochemical, sensory, and microbial effects of the PBCS. A hedonic test was performed with 20 participants who rated appearance, aroma, taste, mouthfeel, and overall acceptability on a 9-point hedonic scale. The results indicated that only liking of mouthfeel was perceived as significantly different, with lime coagulated PBCS receiving the highest rating and significantly higher than the steep water coagulated PBCS, with no difference between either sample to the alum coagulated PBCS. There was a trend for the lime coagulated PBCS to be rated higher for all other attributes, but this was not significant. It should be noted that off-flavors and gritty mouthfeel were not exclusively acknowledged by the authors. This study suggests that lime could be used as a coagulant in order to improve mouthfeel properties, and future studies may want to specifically evaluate the sensory characteristics to determine if this helps to reduce the undesirable gritty characteristic.

In contrast to the studies described above, the following two articles used the largest sample sizes, *n* = 30 and *n* = 50, respectively [25,26], and sensory remained the focal point of the articles. Oyeyinka et al. [25] created soft PBCS while utilizing techniques of blanching soybeans for 30 min prior to blending soy and cashew milks at six different ratios in order to combat the naturally beany flavor of soymilk. The results of a 9-point hedonic test performed with 30 untrained participants (screened for product usage) indicated that blending soy with cashew milk did not result in any significant differences in any measures of liking, including overall acceptability. For this study, it is suggested that the addition of cashews may provide nutritional benefits while having the same level of acceptance among consumers compared to full soy PBCS.

Arise et al. [26] created a soft spreadable PBCS using a fermentation process that combined different blends of soy and almond milk ratios, which was tested in a sensory experiment prepared as breaded and fried. Although beany flavor was not exclusively acknowledged or described as a challenge, it is understood that all soybeans naturally express a beany flavor, and frying the PBCS coupled with the techniques described above will aid in decreasing these naturally undesirable characteristics. Results of a 9-point hedonic test performed with 50 untrained participants screened for "regular cheese consumption" indicated that the fried 70:30 soy to almond milk PBCS sample received the highest ratings in terms of overall acceptability. The 70:30 blend resulted in a significant improvement in overall acceptability compared to the 100% soy control (7.6 vs. 7.0, respectively). However, when looking at liking ratings for taste, color, texture, and aroma there were no significant differences in ratings between the 70:30 blend and 100% soy PBCS, but there was a trend for the 70:30 blend to have higher ratings for taste, color, and texture. Additional sensory studies are needed to determine if this approach results in masking of beany flavors or reducing grittiness. Overall, this study suggests blending soy with almond milk can improve the overall acceptability of PBCS.

#### *3.2. Sensory Profile of Coconut-Based Cheese Products*

Saraco and Blaxland [10] aimed to investigate if PBCS products were able to mimic the physical, sensory, and functional properties of their dairy counterparts or if further improvement would be needed. In contrast to the articles reviewed above, the authors did not create a PBCS but rather employed a descriptive sensory evaluation to assess the product performances between commercially available dairy and non-dairy cheeses in the UK. It was found that of the 109 commercially available PBCS, 74% of these products had coconut oil as their primary ingredient, while only 3% were soy-based. The most abundant variety of PBCS was mild cheddar. Based on these findings, the PBCS products that underwent sensory evaluation were all coconut-based and of the mild cheddar and semi-hard Italian varieties. In the descriptive analysis performed by 1 semi-trained and 3 trained panelists, two mild cheddar PBCS and two semi-hard Italian PBCS varieties were compared to their dairy counterparts and assessed based on their appearance, color, odor, mouthfeel, flavor, and aftertaste. Panelists also reported whether the PBCS products were deemed acceptable compared to their conventional dairy cheese. It was noted that not all PBCS sensory attributes were considered simultaneously comparable to their dairy counterparts. Results of the descriptive analysis concluded that neither the texture or flavor expressed in the semi-hard Italian PBCS were regarded as acceptable. The "yeasty" and "unpleasant onion/garlic" flavors, "oily" mouthfeel, and "sour" aftertaste were deemed potentially unacceptable to consumers compared to the dairy counterpart. While one of the mild cheddar PBCS expressed acceptable texture, the "rancid (intense)" odor, and "intense cheese rind" flavor deemed this sample potentially unacceptable to consumers. The other mild cheddar PBCS sample was the only non-dairy sample to have potentially acceptable attributes. Although the mild cheddar PBCS sample did not have a typical texture found in cheese it was deemed acceptable in both flavor and texture and was described as the following: with a "glossy, cheese-like, smooth" appearance, "pale yellow" color (similar to dairy sample), "waxy/mild/parmesan-like" odor, "oily/rubbery" mouthfeel (less resistance compared to dairy sample), "intense/typical processed cheese-like" flavor, and a "salty" aftertaste. This study demonstrates the wide variety in sensations that are perceived from two types of PBCS. The combination of rating specific sensory and quality attributes along with liking ratings can provide a greater understanding of the product profile and the relationship each attribute to the overall sensory experience, either leading to acceptance or rejection.

#### **4. Review of the Sensory Methods**

Sensory preferences are like a fingerprint, unique to each individual and influenced by many factors but the pulse is fueled by the same source, where consumers' purchase

intention is ultimately driven by taste [32]. Regardless of whether the PBCS, either embraces the natural sensory characteristics of plant-based ingredients or closely mimics conventional dairy products, the finished product should have physical, functional, and sensory properties that consumers find desirable. However, as an instrumental technique, following proper standard protocols helps to increase rigor and minimize bias. While there is established work in PBCS using sensory approaches, common errors in sensory methodology and limitations of the current literature still exist. Below, we highlight some of these errors and limitations and also highlight areas that describe additional considerations when performing sensory evaluation for PBCS.

#### *4.1. Limitations and Considerations for Current Literature*

In the reviewed literature, there were differences in methodologies used, including data collection measures, number of participants, and whether participants received training. Many of the studies reported using trained panels which are known to induce bias when collecting hedonic ratings and may not be representative of the consumer population. While the incorporation of sensory analysis is helpful and suggests that it is a beneficial tool, there is an opportunity to improve upon the sensory methods utilized. There are limitations within the current literature that are notable, suggesting additional work is needed to validate findings. As noted above, the literature repeatedly describes beany flavor and gritty mouthfeel to be "off characteristics" and undesirable in soy products. These studies suggest that modifying fermentation, processing, or blending other plantbased milks approaches improves these sensory characteristics [16–31]. It is described that beany and gritty sensory attributes are reduced; however, no study directly measured these attributes during sensory analysis. To better understand the impact of blending milks and modifying processing steps of PBCS, sensory methods that quantify attributes, such as descriptive sensory analysis, could be performed to determine how these strategies impact sensory attributes such as beany and gritty. Other sensory qualities, such as mouthfeel characteristics, were understudied among these articles and provides an opportunity for future investigation of PBCS. Furthermore, out of the 12 studies reviewed, four did not undergo statistical analysis, and they were, therefore, unable to determine whether a significant improvement was achieved.

It should be noted that a combination of sensory methods can provide a more indepth understanding between the perception of sensory attributes and their impact on liking/disliking. Integrating hedonic, discrimination, and/or descriptive testing can reveal important relationships between the sensory profile and consumer liking [33]. Another advantage is the combination of instrumental analysis with consumer liking. This approach can help to identify the connections between physical attributes with improved liking. For example, several studies reviewed here measured the textural profile which can help to link attributes like hardness and chewiness with consumer ratings of mouthfeel attributes; however, no formal analysis was conducted to better determine how textural attributes affected liking. Future studies can benefit from combining both sensory methods with instrumental analysis to provide a greater understanding of the physical attributes that drive liking and disliking of PBCS.

#### *4.2. Consumers and Future Considerations for Segmentation*

It is important to recruit a large and diverse group of participants screened based on consumption of PBCS or dairy-based cheese. Although smaller pools (*n*~20) are sufficient enough for trial hedonic testing, much larger groups (*n* = 75–150 [33] and even larger *n* = 200–500 [34,35] are crucial for more accurately predicting consumer acceptance in the market. While this process seems straightforward, recruitment for large sampling can be challenging due to screening parameters (i.e., allergies, availability, and product usage) and additional incurred costs, yet, provide a more rigorous/confident response rate. However, screening can provide a better understanding and deeper connection to types of PBCS consumers.

Dairy alternatives were once geared primarily toward consumers who actively avoided dairy due to allergy, intolerance, or a vegan diet. However, this is quickly changing due to emerging plant-based proteins and sensory quality advancements, coupled with concerns over environmental impacts, sustainability, health, and animal welfare, where more adults across dietary spectrums are choosing dairy substitutes [10]. In terms of PBCS and the current market, there are consumers who want to enjoy the nuance and embrace the uniqueness of the plant sensory in PBCS. Jeske et al. [5] explains that a noteworthy approach from manufacturers and consumers would be to appreciate the flavor of plant ingredients [5]. After all, why would a sunflower seed PBCS product not have a flavor profile of sunflower seeds [5]? Yet, there are consumers who expect PBCS to resemble their dairy counterparts in terms of traditional chemical (flavor, taste, and aroma) and physical (meltability and mouthfeel) properties. If the flavor, mouthfeel, or other sensory qualities of the end product are not what the consumer expects, it may result in rejection of that product [36]. With the potential for such a strong consumer segmentation, in the future, it may be worthwhile to further understand the diverse consumer segments of plant-based products. Consumers may also differ in whether the nutritional value of PBCS will influence acceptance, considering the differences in protein quality and calcium content, among other nutritional components, compared to conventional cheese products. If we better understand these consumer categories, it can be used to optimize plant-based materials specifically in PBCS to best cater to these different consumers.

Identifying an appropriate control is paramount for managing expectations and the performance of PBCS. Ultimately, the choice of the control hinges upon the goal of the PBCS, whether it is to embrace the uniqueness of the plant-based milk or to mimic sensory attributes of a dairy counterpart coupled with an all-encompassing consideration of sensory attributes, style, and functionality. Although the underlying goal of the PBCS was not explicitly expressed to the reader in the studies mentioned, it was gathered that there is a link between the goal and the choice of the control used in each study. While most studies used a 100% plant-based milk substitute as a control, three studies used a dairy counterpart [10,16,17]. If the intention is to embrace the natural PBCS attributes, comparing different kinds of PBCS will indicate if further refinement is needed or if the current product can be marketed. On the other hand, if the goal is to create a PBCS that fully mimics the chemical and physical attributes of conventional cheese then a dairy control should be used. Results will determine how the PBCS sensory properties compare to the dairy-based cheese product and depict whether further refinement is necessary or if there was an improvement in the development.

#### **5. Conclusions**

A human's sensory perception is indispensable and the investment in sensory evaluation is imperative. Sensory science is an important part of a product's development in its pre-commercial production life as it acts as the link in the chain which connects producers to consumers. Not only do consumers sometimes have the ability to detect odorants, among other sensory attributes, at lower levels than those of an instrument, but instruments cannot gauge pleasure, or predict liking as humans do [37]. Through the use of sensory evaluation, these studies demonstrate several promising processing techniques that can improve the overall quality (taste and textural) properties leading to increased liking of soy-based PBCS. These studies suggest that modifications in processing and addition of alternative milk products can improve consumer liking.

Emerging plant proteins may help to enhance the quality of PBCS. This can only be determined with the integration of sensory science. In terms of sensory evaluation, the only PBCS to be formally evaluated is limited to products either partially or fully prepared with soy and limited to spreadable products. Although some approaches reviewed here include blending nut milks with soy there are other plant-based ingredients that are used to produce PBCS without the use of soy. Few available studies explore other ingredients (i.e., corn [38], or zein [39] but do not incorporate sensory evaluation. Future research will help to uncover additional strategies along with more diverse plant-based ingredients to increase consumer acceptance of PBCS.

Sensory science can complement ongoing scientific research regarding PBCS in order to directly improve the quality attributes which can lead to more efficient development processes. Through the integration of sensory evaluation, product developers can gain a better understanding of ways to increase liking and acceptance by refining the sensory characteristics (i.e., flavor, meltability, mouthfeel, and aroma). Regardless of whether the PBCS intends to mimic the sensory experience of dairy-based cheese or embrace the naturally occurring flavors of plant-derived PBCS, expanding the product selection will better accommodate a broader audience of consumers which will therefore increase consumer sales.

**Author Contributions:** Conception of the review and identification of the literature, E.C.S. and A.A.N.; drafting of manuscript and tables E.C.S.; critical revision and intellectual content, E.C.S., A.J.K., and A.A.N.; supervision, A.A.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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