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Article

Effect of Processing and Storage of Very-Low-Sugar Apple Jams Prepared with Sugar Substitution by Steviol Glycosides on Chosen Physicochemical Attributes and Sensory and Microbiological Quality

by
Marlena Pielak
and
Ewa Czarniecka-Skubina
*
Department of Food Gastronomy and Food Hygiene, Institute of Human Nutrition Sciences, Warsaw University of Life Sciences (WULS), 166 Nowoursynowska St., 02-787 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(18), 8219; https://doi.org/10.3390/app14188219
Submission received: 13 August 2024 / Revised: 8 September 2024 / Accepted: 10 September 2024 / Published: 12 September 2024
(This article belongs to the Special Issue Feature Review Papers in Section ‘Food Science and Technology')
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Abstract

:
Consumers have become more aware of the impact of nutrition on health, paying attention to the composition and origin of food and looking for natural products. There is a trend towards a “healthy” diet with low-energy foods and a preference for healthier alternatives. This study aimed to assess the technological quality and food safety of very-low-sugar apple jams with steviol glycosides substituting sugar in various quantities. Apple jam variants with SG substitution at concentrations of 30, 50, and 80% selected in preliminary studies were subjected to physicochemical, sensory, and microbiological analyses during storage for 3 and 6 months. The studied jams were sensorily acceptable, and no significant changes in the technological quality of the products were observed, apart from color darkening. The microbiological quality during storage for 3 and 6 months was also satisfactory. The use of a natural sweetener, steviol glycosides, in the production of apple jam was shown to be satisfactory. It resulted in a product with taste and odor similar to conventional jam but with a low energy value. This product is suitable for people with diabetes, people on a restrictive diet, or those who pay attention to a product’s natural features, in line with the clean-label trend.

1. Introduction

Sugar (sucrose) is a commonly used sweetener that gives structure and color to products, and, in the case of preserves (jams, marmalades, preserves, etc.), it also plays a preservative role. A significant amount of sugar is consumed via processed foods. Due to the excessive consumption of added sugar from processed products, nutritional recommendations include limiting sugar in the diet. The WHO recommends reducing free-sugar intake to less than 10% of the total energy intake in adults and children, suggesting that it should be less than 5% [1]. To reduce the intake of simple sugars to the recommended amount, the WHO advocates promoting a healthy diet through measures such as taxing sugar-sweetened beverages, food labeling, and mass media campaigns promoting a healthy diet [2].
Contemporary consumers limit the added sugar in their diet or replace it using sucrose substitutes. The most common way to reduce the amount of sugar in one’s diet is to stop sweetening beverages such as coffee and tea and buy low-sugar products. This is associated with a change to a more health-promoting lifestyle, especially among people with higher education and in a better financial situation. These people are significantly more likely to use sweeteners, including steviol glycosides, and choose low-sugar products by preparing them at home or buying ready-made products at the market [3].
Furthermore, there is an increasing demand for natural food ingredients among consumers. Consumers have become more aware of the impact of nutrition on health and pay attention to what they eat, the origin of food, and its ingredients. They, therefore, look for products with natural properties, consciously checking lists of food additives and product labels, expecting them to be transparent. There is also a growing trend towards a “healthy” diet, including consuming low-energy products and a preference for healthier food alternatives. These products are recommended for people with diabetes or other medical conditions, including obesity, or those who care about their figure and health in general [4,5,6]. Jam is a functional food that is easy and safe to swallow, especially for people suffering from dysphagia [7].
Natural sweeteners are often considered to be more in line with the trend towards a healthy and natural diet than synthetic sweeteners. Currently, consumers seem more willing to try natural alternatives to sucrose [8,9,10]. There has been a meaningful increase in demand for natural sugar substitutes in the food industry. Steviol glycosides obtained from stevia leaves can be used as a food ingredient in food production processes as a healthy, safe, and natural alternative to sucrose and aspartame, e.g., in fruit and tea drinks, dairy products, chocolate, jams, and cookies [11,12,13,14].
Jam is one of the traditional fruit products made to preserve seasonal fruits, which allows them to be consumed out of season. Since a high sugar intake may be associated with a greater risk of metabolic diseases, low-sugar jams are becoming more popular in healthy consumer diets than traditional ones. Thus, the demand for natural products with a reduced energy value among processed fruit products is increasing in the food market [15].
Jams combine sugar, the pulp or puree of one or more types of fruit, water, and gelling agents [16]. There are various strategies to transform traditional recipes into low-sugar versions by reducing the sugar content or using ingredients with functional properties. However, preserving the original organoleptic characteristics of conventional products is still challenging. This is the case for low-sugar jams, as sugar should also be added during production for technological reasons, as it acts as a dehydrating agent for pectin molecules, allowing closer contact between the pectin chains during jam production [17]. Consumers appreciate jams with a low sugar content, in which sweeteners have replaced part of the sucrose [18,19].
In 2011, the European Food Safety Authority adopted a regulation allowing steviol glycosides to be used, among others, in fruit preserves [20]. They are used due to the combination of their sweetening properties with other properties such as resistance to sunlight and high temperature over a broad pH spectrum, which is used in preservation processes (pasteurization, sterilization) [21,22]. They can be successfully used in fruit preserves to reduce simple sugars and lower the glycemic index of the final product. Steviol glycosides do not cause fluctuations in the blood glucose levels, so they are an attractive sugar substitute for people with diabetes [23,24]. Adding steviol glycosides to fruit preserves seems to be a good solution due to their health-promoting, anti-caries, bactericidal, antifungal, and mold growth-inhibiting properties [25,26,27,28,29,30,31,32,33].
Limiting excessive chemical additives and preservatives in food, including fruit products, is difficult because many functional additives, such as sugar, have a preservative effect and are used in food processing to ensure health, safety, and a sufficiently long shelf-life. Therefore, it is essential to know the changes occurring in fruit products with steviol glycosides during storage.
This study aimed to assess the technological quality and health safety of low-sugar apple products with sugar substituted with steviol glycosides. A hypothesis was put forward that it would be possible to obtain apple products with deficient sugar levels using steviol glycosides with an acceptable sensory quality, good physicochemical properties, and microbiological safety.

2. Materials and Methods

According to the Codex Alimentarius [34], the term jam refers to a product brought to a suitable consistency, made from whole fruit, fruit pieces, or unconcentrated and/or concentrated fruit pulp or fruit puree, from one or more types of fruit, which are mixed with food products with specific sweetening properties, e.g., sucrose, with or without added water. In the first stage of this research, a recipe for a base product was established, with the following composition: apple pulp and sugar as the sweetener, with added pectin and citric acid. Then, the sugar was substituted with steviol glycosides (SGs) at 0–100%, and SG additive variants for sensorily acceptable apple jams were selected. Next, the selected apple jams were subjected to further physicochemical, sensory, and microbiological tests while storing the finished products for 0, 3, and 6 months (Figure 1).

2.1. Materials and Preparation of Apple Jams

The research material consisted of apple jams prepared under laboratory conditions from Gloster apples (Malus domestica “Gloster”) from the experimental orchards of WULS. The raw material selected for the tests was of a similar fruit size, healthy, and without mechanical damage. For this study, the starting jam with sugar contained apple pulp and sugar in a ratio of 10:1 (m/m). In preliminary tests, the apple jams were accepted by the sensory panel. It was determined that 1 g of sugar corresponded to 0.01 g of steviol glycosides. After this, the sucrose in the apple jams was replaced successively with the appropriate amount of steviol glycosides at quantities of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100%. Products with a reduced sugar content compared to the sugar variant were marked with the abbreviation VL.
Sugar (DIAMANT; Pfeifer & Langen Polska S.A. (Poznań, Poland) and Pfeifer & Langen Glinojeck S.A. (Glinojeck, Poland)) and highly purified (95.1%, HPLC) steviol glycosides (SGs) in powdered form with rebaudioside A at 40.2% and stevioside at 45.4% (Stevia Natura SAS, Riom, France) and the addition of powdered amidated citrus–apple pectin (Agnex, Białystok, Poland) with a degree of esterification of 30–35 (DE) and 15–20% amination (DA) were used to prepare apple jams. The pectin solution was prepared in the amount recommended by the producer: 3 g per 1 kg of apples. An aqueous solution of citric acid (Agnex, Białystok, Poland) was also used in addition to the previously mentioned ingredients, the addition of which was calculated based on the acidity balance. The quantities of the individual ingredients used to prepare the apple jams are presented in Table 1. The 100% substitution of sugar with steviol glycosides was omitted in further studies due to the lack of sensory acceptance.
A detailed analysis of the apple jams with steviol glycoside substitutions was performed at selected 0, 30, 50, and 80% levels.

2.2. Storage of Jams

All jams were stored in a cool and dry room (10 °C) until four hours before testing, at which point they were stored at room temperature (20 °C). The measurements of color and selected physicochemical, microbiological, and sensory parameters were performed immediately after production and after 3 and 6 months of storage.

2.3. Sensory Analysis

2.3.1. Expert Evaluation

The overall quality of the apple jams was assessed using the sensory profiling method to characterize the flavor and aroma profile of the obtained product. The evaluation conditions were determined in accordance with Civille and Carr [35]. The selection of distinguishing features for sensory analysis was performed using the procedure PN-EN ISO 13299:2016-05 [36]. The evaluation was conducted by a qualified team, who were checked for individual sensory sensitivity and had experience evaluating fruit and vegetable products [37,38].
Samples of apple jam (30 g) were placed in plastic containers and then covered with a lid. After labeling them with a three-digit code, the samples were delivered for evaluation at a temperature of 25 ± 1 °C, together with an evaluation card. Drinking water was provided between trials. Quantitative feature evaluation was performed on an unstructured 10 cm linear scale from 0 to 10 conventional units (c.u.) with appropriate word anchors:
-
odor—apple, sweet, nectar, wine, metallic, sharp, and “other” (none–strong);
-
taste—sweet, bitter, and sour (none–strong);
-
flavor—apple, nectar, spicy (woody), metallic, bland, astringent, and “other” (none–strong);
-
color (light–dark);
-
sensory balance—the degree of harmonization between the sensory attributes (low–high).
The quality attributes were defined in words to unify the evaluation.
For further detailed analyses and storage studies, four levels of sugar substitution by steviol glycosides were selected—0, 30, 50, and 80%—alongside chosen quality parameters that differentiated the products, as found in the first stage of the research. These were color (light–dark), odor (apple, metallic), taste (sweet, bitter), and flavor (apple), and, due to changes during storage, consistency (loose–compact) and the overall quality (bad–very good) were added.

2.3.2. Consumer Evaluation

The consumer tests were conducted according to the PN-EN ISO 1136:2017:08 [39] standard in a group of 120 people aged 18–45, 77% of whom were women. About 75% of the respondents consumed jam occasionally, and about 20% of people consumed jam two-to-three times a week. Nearly 70% of the respondents limited the level of sugar in their diet due to care for their figure (45.6%), health reasons (40.4%), and sensory reasons (14.6%).
The classical hedonic scale method was used to assess the desirability, with a 9-point classic hedonic scale: 9—I like it extremely; 8—I like it very much; 7—I like it quite a bit; 6—I like it moderately; 5—I neither like it nor dislike it; 4—I dislike it a little; 3—I dislike it moderately; 2—I dislike it very much; and 1—I dislike it extremely [40]. The respondents were asked to indicate the product features (color, taste, smell, consistency, etc.) that impacted their assessment the most.
The respondents were free to participate in the research. Because the research was non-invasive and the details of the participants remained undisclosed, this research did not fall within the remit of the Helsinki Declaration.

2.4. Instrumental Color Measurements

The color was measured using a spectrophotometer (CM-2300d, Konica-Minolta GmbH, Langenhagen, Germany) using a D65 light source and an observer angle of 10°.
The results were expressed using the CIE (L*a*b*) system with the following color parameters: L*—lightness (0 means black, and 100 is the maximum light intensity that is still visible without causing damage to the eyes); a*—the proportion of red (+) or green (−); b*—the proportion of yellow (+) or blue (−); and C*—chroma, i.e., color intensity, where C* = √[(a*)2 + (b*)2]. The chroma value, the intensity of color, was calculated using the formula (ΔC) = √((Δa*)2 + (Δb*)2). The total color differences (ΔE) between the samples were calculated according to the following equation: ΔE*ab = √[(ΔL*)2 + (Δa*)2 + (Δb*)2]. The tests were performed at the beginning (0) and after 3 and 6 months of storage.
The color difference in the results can be interpreted as follows:
  • 0 < ΔE* < 1—the difference in color is visually nonrecognizable by a standard observer;
  • 1 < ΔE* < 2—the difference is visually recognizable only by an experienced observer;
  • 2 < ΔE* < 3.5—the difference can be visually recognized by an inexperienced observer;
  • 3.5 < ΔE* < 5—every observer can easily see the difference;
  • ΔE* > 5—an observer recognizes two different colors [41].

2.5. Physicochemical Composition

The physicochemical characterization of the jams included determining the content of selected components (Table 2) at the beginning (0) and after 3 and 6 months of storage. All analyses were conducted in triplicate.

2.6. Microbiological Analysis

The prepared apple jams underwent a microbiological analysis at the beginning and after three and after six months of storage. The results were expressed as “CFU (colony-forming units)/g” in line with the guidelines of APHA [46]. All analyses were carried out in triplicate. The types of microbiological analyses are presented in Table 3.

2.7. Statistical Analysis

The research findings were analyzed using the STATISTICA software, version 13.1 PL (StatSoft, Kraków, Polska). The results of the physicochemical analysis were presented as a mean with standard deviation (SD). The results of the sensory analyses were presented as mean values with standard error (SE). To analyze the results of the physicochemical tests and sensory evaluations (expert and consumer), a one-way analysis of variance (ANOVA) was used, using Fisher’s least significant difference (LSD) post hoc test. Statistical significance was defined at p ≤ 0.05. The results of sensory profiling of the apple jams were analyzed by principal components analysis (PCA) [52].

3. Results

3.1. Optimization of the Addition of Steviol Glycosides to Very-Low-Sugar Apple Jams

The results of the principal component analysis of apple jams with a very low sugar content and SG substitution at 0–90% are presented in Figure 2. The first two principal components explained 81.99% of the total sample variability. In the figure, the ellipses indicate the samples located closest and furthest from the vector of the degree of sensory balance. A high degree of balance in the sensory characteristics of the jams was found at the 0–40% SG substitution (samples: VL0, VL10, VL20, VL30, VL40). This was the result of high scores (>6.6) for nectar odor and flavor (v3, v11), as well as apple flavor (v9). Samples VL80 and VL90 were assessed as products with a lower degree of sensory balance compared to the others (5.0 and 4.9) due to the high intensity of bland flavor (v17), “other” flavor (v18), sour (v12), and bitter (v13) taste assessments (Figure 2). Preliminary studies showed that adding citric acid to apple jam increased the intensity of the apple and nectar odor, the sour taste, and the wine odor and reduced the intensity of the bland flavor and the “other” odor and flavor responses.
In these preliminary studies, further use of VL100 was excluded due to the lack of sensory acceptability of the sample.

3.2. Consumer Evaluation of Very-Low-Sugar Apple Jams with Added Steviol Glycosides

Consumers mentioned taste and smell as the features that most influenced their evaluation of the apple jams. The color and consistency of the jams were mentioned sporadically. Less than 1% of the assessors indicated non-sensory (affective) factors. The assessed jams had high hedonic scores from 5.4 to 7.3 c.u. depending on the degree of sugar substitution with steviol glycosides (Figure 3).
In the case of sugar substitution with SGs at 90%, the scores were significantly worse.
Jams with a higher substitution level of 60–80% were rated better only by people who did not limit their sugar intake (p = 0.001). All jams were rated better by women. Men gave higher ratings to the jam variants with substitution levels of 30, 40, 50, and 60% (samples VL30, VL40, VL50, VL60).
The increase in the level of sucrose substitution with SGs was negatively correlated with the degree of hedonic evaluation of the jams (r = 0.28; p < 0.001). The first statistically significant difference in assessing the desirability of the jams was visible at a 20% addition of SGs. In summary, consumers rated apple jams with a very low sugar content with the addition of SGs better compared to panelists. High evaluations of jams were also found in the group of young consumers aged 18–25.

3.3. The Effect of Storage on the Sensory Quality of Very-Low-Sugar Apple Jams with Added SGs

Selected apple jams (VL30, VL50, and VL80) with sugar and substitution SGs were evaluated at the beginning and after 3 and 6 months of storage. The results are presented in Figure 4.
Jams with increased SG addition were rated slightly lower regarding their sweet taste (except for the 80% level), apple flavor, color, and consistency than jams with only sugar. The sweet taste ratings varied from 6.4 to 7.6 c.u., and the apple flavor was between 7.0 and 8.5. A higher variation was found between jams with different levels (0–80%) of SG substitution for apple odor (6.1–8.7), color (3.8–5.3), and consistency (5.5–8.5 c.u.). The perception of the bitter taste and metallic odor of apple jams was significantly higher with increasing SG substitution levels (p < 0.001) and a storage time of the jams of up to 3 months (p < 0.05). In the case of metallic odor, this relationship was not found for the 80% SG addition. The overall quality of very-low-sugar apple jams also decreased with the increase in SG addition from 8.5 (0% SGs) to 5.8 (80% SGs) and storage time from 0 to 6 months. This could be due to a higher negative note, i.e., bitter taste and metallic odor.
The very-low-sugar apple jams with SGs had a relatively light color, which darkened significantly after 3 and 6 months of storage (Figure 4). The lighter color of the jams with additional steviol glycosides compared to conventional jams with sugar was due to the caramelization of the sugar during the technological process. The additives used, such as pectin and citric acid, also impacted the lightening of the color. With the addition of steviol glycosides to the jams and, thus, a reduction in the sugar content, the jam samples were lighter (Table 4). They were characterized by a yellow color, which became more visible with an increasing SG content. It can be stated that the addition of citric acid stabilized the color, and the observed changes in the ΔE parameter ranged from 1.33 to 2.18 depending on the addition of SGs (Table 4). All the tested jams with steviol glycosides were initially characterized by yellow (positive value of the Δb parameter) and low color saturations (ΔC parameter).
After storage, the color of all the jam samples darkened (the ΔL value was negative), and the samples were characterized by a stronger red color compared to the jams assessed at the beginning of storage (negative Δa values); however, these changes were not significant. After storage, the yellow color of the jams also changed; the jams were more blue than yellow (negative Δb values).

3.4. The Effect of Storage on the Physicochemical Parameters of Very-Low-Sugar Apple Jams with Added Steviol Glycosides

After preparation, the content of total soluble solids (%) in the jams was 45.5, and the substitution of sugar with steviol glycosides led to a statistically significant change in content, up to 39.0. The prepared jams contained 95% of raw materials (apples), and the extract of apples used to prepare the preserves was 16.3%. With the increase in steviol glycosides, a statistically significant (p ≤ 0.05) decrease in the dry matter content and total extract was observed (Table 5). The very-low-sugar product with the 80% SG substitution had an extract similar to that of raw apple. The storage of the jams for 3 and 6 months did not cause significant changes in the dry matter (p > 0.05), which may indicate that adding citric acid and pectin stabilizes the composition and limits some physicochemical changes.
The vitamin C content in all the jams was not high, and there was no strong correlation between its content and the addition of steviol glycosides (r = 0.32). During jam storage, significant changes in vitamin C were found in the jams, with p ≤ 0.05 (Table 5), in the range from 29 to 75%, regardless of the jams’ composition (addition of SGs and sugar).
The total ash content in the evaluated apple jams was related to the level of SG substitution (r = 0.64, p < 0.001) and the jam storage time (r = 0.66; p < 0.05). After six months of storage, an increase in its content was observed, which may indicate more minor changes occurring in the jams due to, for example, a stabilizer such as citric acid.
In all the jams, the pH was maintained in the range of 3.2–3.48. The addition of pectin and citric acid stabilized the pH of the jams. The pH value in the evaluated jams was related to the level of SG substitution (r = 0.64, p < 0.001) and the storage time (3, 6 months) (r = 0.64, p < 0.05).
A similar relationship was found for acidity. With increasing SG addition, titratable acidity and the acidity expressed as malic acid increased (r = 0.74 and r = 0.91, p < 0.05, respectively). The same relationship was found after storage for 3 and 6 months (r = 0.76 and r = 0.94, p < 0.05, respectively). The total acidity expressed as malic acid content depends on the initial content of organic acids. In the raw apples used to prepare the jam, it was 0.42 g of malic acid per 100 g; after processing, this increased in the control sample (Table 5). The total acidity of the very-low-sugar apple jams decreased significantly only in the variant with sugar content, suggesting that substitution with steviol glycosides did not consistently stabilize this parameter. This could impact the product’s overall quality and shelf life, as acidity is critical in preventing microbial growth and ensuring product safety during storage.

3.5. The Effect of Storage on the Microbiological Quality of Very-Low-Sugar Apple Jams with Added Steviol Glycosides

The microbiological quality assessment carried out at the beginning of the storage cycle and after storage for 3 and 6 months did not show the presence of Listeria monocytogenes and coagulase-positive staphylococci (Table 6). The content of yeasts and molds and the total number of microorganisms (OLD at 30 °C) were satisfactory, below 10.
Therefore, the microbiological quality of the jams was good and did not change during storage for 3 and 6 months, regardless of the level of sugar substitution with steviol glycosides.

4. Discussion

The effect of sugar substitution with SGs on the sensory quality of very-low-sugar apple jams was evaluated in this study.
The sensory evaluation results showed that a high amount of sugar substituted with steviol glycosides (up to 90%) reduced the desirability of the very-low-sugar apple jams, even though the amounts used were small. Compared to low-sugar apple products with the addition of steviol glycosides, their sensory quality was better, as demonstrated in previous studies [11]. The low-sugar products were characterized by a more intense sweet taste and a darker color due to the higher sugar content. They also had a higher intensity of responses regarding metallic and “other” taste and odors, as well as a sharp odor, a bitter taste, an astringent sensation, and a bland flavor, which consequently influenced the sensory balance of the products [11].
Other authors also point to an increase in the intensity of metallic, licorice, and other negative flavors instead of sweet and fruity flavors [56,57,58]. This is associated with a dominant bitter taste and a reduced perception of sweet taste, which is explained by intermolecular cross-suppression between steviol glycosides responsible for sweet and bitter tastes [58,59]. Therefore, using low levels of steviol glycosides, as in the case of this study, improved the taste, eliminating the bitter taste of licorice. Prakash et al. [60] suggest that steviol glycosides should constitute 20–80% of the sweetness, with sucrose accounting for the rest, obtaining characteristics similar to sugar use. The sensory quality of very-low-sugar apple jams with a 50% SG substitution level did not differ significantly from the control sample, i.e., jam with only sugar. It should also be emphasized that adding pectin and citric acid may mask the negative effect of steviol glycosides, increasing the natural flavor of apple products, i.e., the wine or apple flavor, thus allowing for the possibility of increasing the addition of SGs. Similar data are reported by Yosefi et al. [61] for quince jam and by Carvalho et al. [26] for strawberry jam.

4.1. The Effect of Storage on the Sensory Quality of Very-Low-Sugar Apple Jams with Sugar Substitution by SGs

For consumers and food producers, the sensory properties of food products are essential because they directly relate to the product’s quality and further consumer acceptance. A product’s quality assessment is based on sensory indicators such as color, odor, taste, and consistency.
In the studied jams, the sugar content was reduced by substituting it with steviol glycosides, which were sensorily accepted by the evaluators. Adding pectin and citric acid to apple jams with added steviol glycosides improves their sensory quality. It stabilizes the color and physicochemical composition, and, as mentioned earlier, it can mask the adverse effects of SGs, thus enhancing the natural flavor properties of apple products, i.e., wine or apple flavors, as demonstrated in previous studies [11].
Storage time did not significantly affect sensory changes in the very-low-sugar jams (overall quality parameters in the range of 8.5–5.5 c.u., depending on the level of substitution and the storage time). The highest overall quality was noted for the jam with a 30% substitution with steviol glycosides. Moreover, after 3 and 6 months of storage, no statistically significant differences were found in terms of bitter, sweet, or apple taste, i.e., characteristic features of apple jams.
Similar results were also indicated by other authors who showed high sensory quality scores of jams with SG substitution after the preparation and storage of cherry jams [62] and strawberry jams [63]. After 12 months of storing cherry jams, only a slight decrease in the intensity of the cherry flavor was observed [64].
In all stored jams, the color darkened, and the darkest color was characteristic of samples containing only sucrose. Color changes may result mainly from Maillard reactions and the formation of non-enzymatic browning products. A similar observation was made by Banaś et al. [65] regarding Japanese quince jams with the addition of wheat and flax seeds with steviol glycoside substitution. Our studies demonstrated a stabilizing effect on the color of jams with steviol glycosides, citric acid, and pectin. A slight deterioration in consistency occurred in all stored jams compared to the sample taken immediately after production, which may have been influenced by the decomposition of pectin compounds by the acids contained in the jam, resulting in the loosening of the consistency, as mentioned by other authors [64,65].

4.2. The Effect of Sugar Substitution with SGs on Physicochemical Parameters and Microbiological Quality of Very-Low-Sugar Apple Jams and Changes during Storage

In the processing and storage processes, losses of a large part of nutrients and bioactive ingredients occur, mainly during the pasteurization or sterilization of products. This can translate into the technological quality of the product, which can be improved through appropriate parameters in the preparation process but also by optimizing the share of ingredients in the product.
The very-low-sugar jams made from Gloster apples had an elemental chemical composition (dry matter, vitamin C, total acidity, pH, and ash) similar to their traditional counterparts. The stored products made from apples with added steviol glycosides had a higher water content (53–62%) after production, possibly due to the traditional production process for jams [66,67]. This may have resulted in a shorter storage time.
During changes in the quality of processed foods, particularly changes in color during storage, the storage method and temperature play an important role. Many authors [68,69,70,71] have observed darkening and quality changes in fruit products, including jams, during storage, especially at higher temperatures. The technological quality of the products tested in this study after storage was acceptable. It should be emphasized that the jams evaluated in this study were stored under refrigerated conditions. Citric acid and the addition of pectin in products with steviol glycosides influenced the stabilization of the composition and the limitation of the occurring physicochemical changes.
The total acidity is one of many physicochemical parameters influencing product quality, because it protects the product against developing microorganisms. In our studies, the total acidity only decreased significantly in the very-low-sugar apple jam sample with sugar content. The content of steviol glycosides had no significant effect on the stabilization of total acidity, and both an increase and decrease in total acidity were observed during a storage period of six months. Depending on the SG substitution and storage time, the pH varied but remained similar despite statistically significant differences in the range of 3.15–4.09.
In a study of apricot jam after storage, Touati et al. [72] noted an increase in total acidity. These authors showed a significant effect of the time–temperature interaction on the pH of apricot jams (p < 0.05), which decreased to 3.39 and 3.34 after long-term storage at 5 °C and 25 °C.
Jams are characterized by a low vitamin C content due to their production method, and this amount decreases by up to five times during storage [73]. In the case of our apple jams, it can be stated that substituting sugar with steviol glycosides did not inhibit vitamin C degradation during storage. Similar results were obtained by Tobal et al. [74], who found that vitamin C degradation occurred after a shorter storage time in jams with added sweeteners than in conventional jams. However, other authors indicate that, compared to other sweeteners, adding steviol glycosides increases the storage stability of most bioactive compounds, especially vitamin C [75].
It should be emphasized that the studied jams stored for 3 and 6 months at 10 °C were of good microbiological quality. Other authors have indicated similar results of microbiological assessments of jams with steviol glycosides regarding molds and yeasts. No changes in the microbiological quality were observed after 30 days of storage of strawberry jams [26,31] and after six months of storage of pomegranate jam [25]. However, Savita et al. [76] reported that, in the multi-fruit jam with steviol glycosides that they studied, microbial growth was detected during the fifth week of storage.

4.3. Limitations

The main limitation on the practical use of the obtained results is the high purity of the steviol glycosides, which is not often observed in industrial practice due to the high costs of such preparations. This could have had an impact on the better sensory quality of the jams because the higher the purity of rebaudioside A or stevioside, the lower the intensity of the bitter aftertaste, thereby artificially improving the sensory quality of the jams. In typical industrial scenarios, where steviol glycosides of a lower purity might be used, the sensory quality of the product might not be as favorable. Therefore, this study’s results might not fully represent real-world applications.

5. Conclusions

In very-low-sugar apple jams, reducing the sugar content by substituting it with steviol glycosides by up to 80% (0.08 g 100 g−1) was possible. Higher levels of substitution resulted in a deterioration in taste and odor and a notably higher intensity of metallic and sharp odors, as well as metallic flavor, bitter taste, and astringent sensation.
The selected jams with steviol glycoside substitutions at 30, 50, and 80% were sensorily acceptable, and the tests did not reveal any significant changes in the technological quality of the products, apart from the darkening of the color. The microbiological quality of the apple jams was also satisfactory. It has been shown that using natural sweeteners, such as steviol glycosides, for producing apple jam is satisfactory, resulting in a product with jam-like characteristics—taste and odor similar to conventional jams but with a low energy value. This product type may be suitable for people with diabetes, people on a restrictive diet, or those who pay attention to a product’s natural qualities in line with the clean-label trend. The obtained results should be further investigated using steviol glycosides in terms of the quality parameters commonly used in industrial production to develop a marketable product. This would help develop a market-ready product that balances sensory quality, technological performance, and consumer acceptability while aligning with industry standards and practices.

Author Contributions

Conceptualization, E.C.-S. and M.P.; methodology, E.C.-S. and M.P.; formal analysis, M.P.; investigation, M.P.; data curation, E.C.-S. and M.P.; writing—original draft preparation, E.C.-S. and M.P.; writing—review and editing, E.C.-S. and M.P.; visualization, E.C.-S. and M.P.; supervision, E.C.-S.; project administration, E.C.-S.; and funding acquisition, E.C.-S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financed by the Polish Ministry of Science and Higher Education with funds from the Institute of Human Nutrition Sciences, Warsaw University of Life Sciences (WULS) for scientific research.

Institutional Review Board Statement

Ethical review and approval were not obtained for this study, due to Polish regulations did not require the consent of an ethics committee for this type of study.

Informed Consent Statement

Informed consent was obtained from all the subjects involved in this study.

Data Availability Statement

The data presented in this article are available upon reasonable request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 14 08219 g001
Figure 1. Study design.
Figure 1. Study design.
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Figure 2. Principal components analysis (PCA) biplot of apple jams with a very low sugar (VL) content with steviol glycosides: VL0–VL90—samples with 0–90% SG substitution; v1—apple o.; v2—sweet o.; v3—nectar o.; v4—wine o.; v5—metallic o.; v6—sharp o.; v7—“other” o.; v8—color; v9—apple f.; v10—sweet t.; v11—nectar f.; v12—sour t.; v13—bitter t.; v14—spicy f.; v15—metallic f.; v16—astringent t.; v17—bland f.; v18—other f.; v19—sensory balance; o.—odor; f.—flavor; and t.—taste.
Figure 2. Principal components analysis (PCA) biplot of apple jams with a very low sugar (VL) content with steviol glycosides: VL0–VL90—samples with 0–90% SG substitution; v1—apple o.; v2—sweet o.; v3—nectar o.; v4—wine o.; v5—metallic o.; v6—sharp o.; v7—“other” o.; v8—color; v9—apple f.; v10—sweet t.; v11—nectar f.; v12—sour t.; v13—bitter t.; v14—spicy f.; v15—metallic f.; v16—astringent t.; v17—bland f.; v18—other f.; v19—sensory balance; o.—odor; f.—flavor; and t.—taste.
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Figure 3. Consumer evaluation of very-low-sugar apple jams (n = 120). a–e—samples marked with the same letters do not significantly differ statistically; and c.u.—conventional units.
Figure 3. Consumer evaluation of very-low-sugar apple jams (n = 120). a–e—samples marked with the same letters do not significantly differ statistically; and c.u.—conventional units.
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Figure 4. Changes in the sensory quality of very-low-sugar apple jams with steviol glycosides after storage for 3 and 6 months: t.—taste; f.—flavor; and o.—odor.
Figure 4. Changes in the sensory quality of very-low-sugar apple jams with steviol glycosides after storage for 3 and 6 months: t.—taste; f.—flavor; and o.—odor.
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Table 1. The composition of very-low-sugar apple jams for 100 g of apple pulp.
Table 1. The composition of very-low-sugar apple jams for 100 g of apple pulp.
VariantSugar
(g)		Steviol GlycosidesPectin
(g 100 g−1)		Citric Acids
(g 100 g−1)
(g)(%) *
VL0100.0000.30.52
VL1090.01100.30.51
VL2080.02200.30.50
VL3070.03300.30.49
VL4060.04400.30.48
VL5050.05500.30.46
VL6040.06600.30.45
VL7030.07700.30.44
VL8020.08800.30.43
VL9010.09900.30.42
VL10000.101000.30.41
* Percentage of sugar substitution with steviol glycosides; and VL, very-low-sugar variants.
Table 2. The determination of the physicochemical composition.
Table 2. The determination of the physicochemical composition.
ContentMethod
Dry matterPN-A-75101-02:1990 [42]
Total ashPN-90/A-75101-08/Az1:2002 [43]
Total soluble solidsmeasured using the refractometric method according to PN-A-75101-02:1990 [42]
pHmeasured with the potentiometric method using pH-meter Knick 913 (Elektronische Messgeräte, GmbH & Co. KG, Berlin, Germany) according to EN 1132:1994 [44]
Titratable acidityISO 750:1998 [45]; the results were expressed as mg g−1 of malic acid equivalent (MAE)
Vitamin Cmeasurement conducted by high-performance liquid chromatography according to the method presented in a previous study [11]
Table 3. Microbiological analysis.
Table 3. Microbiological analysis.
MicroorganismsMethod
Listeria monocytogenesPN-EN ISO 11290-2:2000+; A1:2005+Ap1:2006+Ap2:2007 [47]; PN-EN-ISO 11290-2:2017-07 [48]
Coagulase-positive staphylococciPN-EN ISO 6888-2:2001+A1:2004 [49]
Total number of colonies at 30 °CPN-EN ISO 4833-1:2013-12 [50]
Yeast and mold countsPN-EN ISO 21527-2:2009 [51]
Table 4. Color assessment of very-low-sugar apple jams (VL) with added steviol glycosides (average value ± SD).
Table 4. Color assessment of very-low-sugar apple jams (VL) with added steviol glycosides (average value ± SD).
Color
(L*a*b*)		Addition of SGs (%) to Very-Low-Sugar (VL) Jams
0305080
Color of Apple Jams at the Beginning of Storage *
L*32.6 ± 0.7433.89 ± 0.6134.1 ± 0.5634.53 ± 0.06
ΔL-1.291.51.93
a*−0.39 ± 0.02−0.41 ± 0.19−0.44 ± 0.36−0.48 ± 0.01
Δa-−0.02−0.05−0.09
b*15.77 ± 0.7816.1 ± 0.6516.31 ± 0.4816.79 ± 0.09
Δb-0.330.541.02
C15.7616.0916.3016.78
ΔC-0.330.541.02
(ΔE)-1.331.602.18
Color change after 3 months of storage **
L*32.51 ± 0.7433.43 ± 0.0133.87 ± 0.0134.21 ± 0.2
ΔL−0.09−0.46−0.23−0.32
a*−0.05 ± 0.02−0.38 ± 0.02−0.43 ± 0.01−0.44 ± 0.02
Δa0.020.030.010.04
b*15.47 ± 0.0215.3 ± 0.1315.85 ± 0.0516.19 ± 0.04
Δb−0.3−0.8−0.46−0.18
C15.7615.2915.8416.18
ΔC0.30.80.460.18
(ΔE)0.30.920.510.37
Color change after 6 months of storage **
L*32.38 ± 0.0133.18 ± 0.0133.63 ± 0.0133.9 ± 0.2
ΔL−0.22−0.71−0.47−0.63
a*−0.15 ± 0.08−0.32 ± 0.22−0.36 ± 0.16−0.4 ± 0.09
Δa0.240.090.080.08
b*15.47 ± 0.0215.55 ± 0.1315.84 ± 0.0515.9 ± 0.04
Δb−0.3−0.55−0.47−0.89
C15.7615.5415.8315.89
ΔC0.380.560.480.89
(ΔE)0.380.90.671.09
* Color changes compared to jam with only sugar (control sample) and ** color changes compared to jam at the beginning of storage. Interpretation of color difference: 0 < ΔE < 1, the difference in color is visually nonrecognizable by a standard observer; 1 < ΔE < 2, the difference is visually recognizable only by an experienced observer; and 2 < ΔE < 3.5, the difference can be visually recognized by an inexperienced observer.
Table 5. Changes in selected physicochemical parameters in very-low-sugar apple jams with SGs.
Table 5. Changes in selected physicochemical parameters in very-low-sugar apple jams with SGs.
SGs
(%)		Time of StorageAverage Value ± SD
Dry Matter
(%)		Vitamin C (mg/100 g)Total Ash
(%)		pHTitratable Acidity (°)Malic Acid
(g/100 g)
0024.7 ± 0.2 ax0.58 ± 0.02 ax0.184 ± 0.012 ax3.48 ± 0.02 ax8.53 ± 0.04 ax0.573 ± 0.003 ax
325.0 ± 0.1 a0.41 ± 0.01 b0.234 ± 0.008 b3.30 ± 0.08 b10.32 ± 0.03 b0.691 ± 0.002 b
625.1 ± 0.3 a0.22 ± 0.01 c0.334 ± 0.004 c3.12 ± 0.02 c13.90 ± 0.10 c0.931 ± 0.001 c
30020.9 ± 0.2 ay0.56 ± 0.02 ax0.231 ± 0.017 ay3.41 ± 0.02 ay13.80 ± 0.25a y0.927 ± 0.002 ay
320.7 ± 0.6 a0.37 ± 0.02 b0.250 ± 0.009 b3.36 ± 0.01 b14.78 ± 0.24 b0.970 ± 0.031 b
621.7 ± 1.0 a0.22 ± 0.01 c0.284 ± 0.004 c3.28 ± 0.03 c16.80 ± 0.40 c1.126 ± 0.004 c
50017.9 ± 0.2 az0.55 ± 0.01 ax0.228 ± 0.009 ay3.44 ± 0.01 az15.81 ± 0.01 az1.060 ± 0.001 az
318.3 ± 0.3 a0.34 ± 0.01 b0.235 ± 0.007 a3.40 ± 0.01 b14.88 ± 0.07 b0.993 ± 0.006 b
618.9 ± 0.6 a0.18 ± 0.01 c0.250 ± 0.002 b3.27 ± 0.02 c14.18 ± 0.05 c0.884 ± 0.004 c
80016.9 ± 0.1 av0.57 ± 0.02 ax0.230 ± 0.030 ay3.38 ± 0.01 ay17.80 ± 0.20 av1.193 ± 0.020 av
316.4 ± 0.9 a0.33 ± 0.01 b0.285 ± 0.060 b3.29 ± 0.01 b16.87 ± 0.31 b1.127 ± 0.021 b
616.3 ± 0.0 a0.14 ± 0.03 c0.320 ± 0.042 b3.20 ± 0.06 b16.50 ± 0.30 b1.033 ± 0.025 c
a, b, and c—samples marked with the same letters do not significantly differ statistically (in columns, between storage times) (p > 0.05); and x, y, z, and v—samples marked with the same letters do not significantly differ statistically (p > 0.05) (in columns, between SG additions of 0, 30, 50, and 80%, without storage)
Table 6. Microbiological quality assessment of very-low-sugar apple jams with SG substitution.
Table 6. Microbiological quality assessment of very-low-sugar apple jams with SG substitution.
SGs
(%)		Storage
(Month)		Coagulase-
Positive
Staphylococci *		Listeria monocytogenes **Yeast ***Mold ***Total Number of Colonies at 30 °C ****
[CFU/g]
00n.d.n.d.<10<10<10
3n.d.n.d.<10<10<10
6n.d.n.d.<10<10<10
300n.d.n.d.<10<10<10
3n.d.n.d.<10<10<10
6n.d.n.d.<10<10<10
500n.d.n.d.<10<10<10
3n.d.n.d.<10<10<10
6n.d.n.d.<10<10<10
800n.d.n.d.<10<10<10
3n.d.n.d.<10<10<10
6n.d.n.d.<10<10<10
n.d., not detected; * and ** absent in 25 g; *** below 10 CFU/g; and **** below 103 CFU/g. The results are considered satisfactory [53,54,55].
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Pielak, M.; Czarniecka-Skubina, E. Effect of Processing and Storage of Very-Low-Sugar Apple Jams Prepared with Sugar Substitution by Steviol Glycosides on Chosen Physicochemical Attributes and Sensory and Microbiological Quality. Appl. Sci. 2024, 14, 8219. https://doi.org/10.3390/app14188219

AMA Style

Pielak M, Czarniecka-Skubina E. Effect of Processing and Storage of Very-Low-Sugar Apple Jams Prepared with Sugar Substitution by Steviol Glycosides on Chosen Physicochemical Attributes and Sensory and Microbiological Quality. Applied Sciences. 2024; 14(18):8219. https://doi.org/10.3390/app14188219

Chicago/Turabian Style

Pielak, Marlena, and Ewa Czarniecka-Skubina. 2024. "Effect of Processing and Storage of Very-Low-Sugar Apple Jams Prepared with Sugar Substitution by Steviol Glycosides on Chosen Physicochemical Attributes and Sensory and Microbiological Quality" Applied Sciences 14, no. 18: 8219. https://doi.org/10.3390/app14188219

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