Utilization of By-Products from the Fruit and Vegetable Processing Industry in Pasta Production

Abstract

Pasta is a product made from wheat semolina and water. Due to its composition and low glycemic index, it is an ideal product for fortification with additional nutrients. Most plant-based food by-products are rich in nutrients of interest, such as fibers, vitamins, minerals, and bioactive compounds. Fortifying pasta with plant-based by-products can be nutritionally beneficial, and the number of publications on this topic has increased significantly in recent years. However, it presents a challenge when aiming to achieve products with good organoleptic quality. This review analyzes the published information on the effect of including plant-based by-products on the technological quality (optimal cooking time, solid loss, swelling index, and water absorption during cooking, color, and texture), nutritional value, and organoleptic properties of pasta. It also provides a critical perspective on gaps in the current knowledge and highlights aspects that should be addressed in the future.

1. Introduction

According to the Food and Agriculture Organization (FAO) [1], one-third of all food produced globally for human consumption is wasted. This waste leads to the squandering of land, water, energy, labor, and, in general, money. Moreover, it imposes an environmental cost as it contributes to greenhouse gas emissions [2]. Among all sectors of the food industry, the fruit and vegetable sector generates the highest percentage of by-products, up to 50%, in the form of peels, cores, pomace, immature and/or damaged fruits and vegetables [3]. Fruits and vegetables are also the most discarded products in distribution, partly due to their short shelf life. Traditionally, these residues have been used for animal feed, fertilizers, or anaerobic digestion. However, organizations such as the United Nations Environment Programme, the European Commission, FAO, the World Resources Institute, among others, assert that reintegrating these residues into the human food chain is preferable to other uses.

The composition of these residues depends on the type of fruit or vegetable processed and the processing method (canning, jam, juice, etc.). In general, these by-products are characterized by a high fiber content [3], and in many cases, they are rich in bioactive components, such as phenolic compounds, which confer a high antioxidant capacity [4,5]. These features make them nutritionally valuable ingredients, but in many cases, they have an unpleasant texture and taste, which limits their incorporation into food products to small amounts. In recent years, studies on the extraction of fibers and bioactive components from fruit and vegetable residues have increased. However, these applications do not fully consume the residues, often leaving a significant amount of new waste. Therefore, the potential utilization of the entire residue is generally a better option from an environmental perspective.

In most cases, these by-products have a high water content and a heavy organic load, which leads to rapid spoilage due to the action of various enzymes and microorganisms [6]. Therefore, it is usually necessary to dry and mill them to produce powders with a long shelf life and easy incorporation into various formulations. Beyond the origin and composition of the residues, the drying and subsequent milling processes also affect the characteristics of these ingredients.

Studies on incorporating these by-products into bakery products have significantly increased and have been the subject of various scientific reviews [7,8,9,10]. Research on the use of these ingredients in various types of pasta has also grown, and although there is a relatively recent review [11], the number of new studies is substantial, warranting an updated review of the literature. Figure 1 shows the number of articles on the incorporation of by-products in pasta published in SCI journals, demonstrating a clear increase in recent years.

Several reviews have been published on the composition and characteristics of by-products derived from fruit and vegetable processing, focusing on their nutritional components [12,13,14,15,16]. There are also reviews focusing on by-products from specific fruits or vegetables, such as banana [17], apple [18,19], grape [20,21], mango [22,23,24], citrus [23,25], berry [26], as well as those derived from processes like winemaking [27]. Brewer’s spent grain and residues from other alcoholic beverages have also been addressed in various reviews and are among the most studied by-products of the plant-based industry [28,29,30]. For this reason, this review will not delve into these aspects but will focus on the applications of these by-products in pasta production. Neither legal issues nor consumer attitudes towards such products will be addressed here. These factors are evolving, driven by increased awareness among authorities and consumers, as well as more accessible information, but they must be considered when marketing these products.

2. Pasta

Pasta is a traditionally Italian cereal-based product, highly appreciated and consumed worldwide due to its sensory quality, ease of preparation, low cost, and long shelf life [31]. The term “pasta” refers to a wide variety of products that differ in shape (e.g., macaroni, spaghetti, bows, tagliatelle, noodles, etc.), processing methods, ingredients, and shelf life. Since pasta is typically made only with durum wheat semolina and water, it is rich in complex carbohydrates and naturally low in fats and simple sugars. Additionally, it has a lower Glycemic Index (GI) than other cereal-based products [32]. Pasta, when consumed as part of a low-GI dietary pattern, does not adversely affect adiposity and even reduces body weight and Body Mass Index compared with higher GI dietary patterns [33]. However, it provides little in the way of other nutrients such as fiber or bioactive components [11].

The processing of pasta has been recently reviewed by Bresciani et al. [34]. A key factor in pasta production is the raw materials. It is widely recognized that durum wheat semolina is the ideal raw material for producing high-quality pasta [35,36]. In fact, in Italy, the world’s leading producer and consumer of pasta, it is forbidden to make pasta with other types of flour [34]. Durum wheat (Triticum durum) has different characteristics from soft wheat (Triticum aestivum), such as greater hardness, higher carotenoid content, lower lipoxygenase activity, and, in general, a higher protein content and gluten strength than other wheat flour types [37]. Its greater hardness allows for higher yields in the production of semolina, which leads to pasta with better culinary qualities than flour-based pasta. The particle size of durum wheat semolina also plays a crucial role in pasta quality [34]. Moreover, its higher carotenoid content contributes to a more intense yellow color, while the lower presence of lipoxygenases helps preserve this color during processing. Additionally, the higher protein content and the gluten characteristics of durum wheat improve the quality of the resulting pasta. Pasta can be made with durum wheat semolina or a combination of soft wheat flour and semolina. The use of soft wheat is common in some countries due to its lower cost or the limited availability of durum wheat. However, this practice negatively affects pasta quality.

Regarding the production process, pasta is made by mixing semolina and other ingredients with water and applying mechanical force to develop the gluten network. Additionally, these operations can be done under vacuum to reduce oxidation of color-related components and minimize air bubbles in the final product [38]. Part of the mechanical work involves low-temperature extrusion, which also shapes the pasta, although in some cases, pasta can be made by rolling. A critical final step is drying, which extends the product’s shelf life. This drying process is crucial and must be adapted depending on the quality of the raw materials [39], and it should be optimized in terms of temperature, relative humidity, and time when new ingredients are introduced [40]. This is attributed to the varying enzymatic activity present in different ingredients, which can influence biochemical reactions during processing. However, the most significant impact lies in the structural modifications induced in the gluten network, affecting its elasticity, strength, and overall integrity. These changes in the composition alter the water absorption capacity of the dough, ultimately influencing the texture, cooking properties, and quality of the final pasta. Fresh pasta, which has a higher moisture content and shorter shelf life, can also be marketed.

Due to its widespread consumption, low cost, and good nutritional characteristics, pasta is an ideal product for fortification or the incorporation of by-products and food waste rich in fiber, vitamins, minerals, and bioactive compounds. In fact, the United States Food and Drug Administration (FDA) has considered pasta to be an ideal food for incorporating bioactive compounds [41]. Numerous studies have been conducted on enriching various types of pasta with nutritionally beneficial ingredients [42,43,44]. However, incorporating ingredients derived from these food matrices rich in bioactive components can introduce unfamiliar flavors, alter the product’s color, and interfere with dough structure, particularly the gluten network, affecting both the culinary quality and the organoleptic properties of the final product. These aspects must be carefully studied and minimized. In most cases, these factors limit the amount of such ingredients that can be incorporated into the pasta. Oliviero and Fogliano [45] analyze the challenges and suggest solutions to increase vegetable consumption through pasta enrichment.

The most studied quality factors in pasta include its culinary properties (optimal cooking time, loss of components during cooking, swelling index, water absorption, etc.), texture, color, nutritional quality, and antimicrobial activity. However, when new ingredients are introduced, factors like flavor and aroma, which strongly influence consumer preferences but cannot be measured instrumentally, become important. Sensory and acceptability analyses of these new products are necessary to assess their market potential.

3. Incorporation of By-Products

3.1. By-Products Treatments

By-products from fruits and vegetables, as well as some obtained from cereal processing, have high moisture content and, therefore, low microbiological stability. To enhance their stability and extend their shelf life, in various scientific studies, these by-products are typically processed using drying methods, such as hot air drying (45–77 °C for 6–48 h) and freeze-drying, followed by milling. Brewery spent grains are also generally dried at temperatures ranging from 35 to 60 °C for 16–72 h. Specific treatments include blackcurrant pomace subjected to extrusion [46], fig peels vacuum-dried at 45 °C for 10–15 h [47], hazelnut skins roasted at 150–155 °C for around 35 min [48], and orange pomace and cucumber peel powder microwaved at 180 W for 40 min [49]. The effect of these treatments on by-products and their influence on the quality of the resulting pasta has been minimally studied.

After drying, grinding is necessary to obtain a powder or flour. As previously stated, the particle size of durum wheat semolina significantly influences pasta quality [34]. However, the particle size of by-products incorporated in pasta production has received little attention. Many of these studies do not specify the particle size of the incorporated by-product. In others, a particle size is provided, usually smaller than a certain number of microns. These numbers can vary from less than 100 microns to less than 1000 microns, and, therefore, can be ten times larger, as shown in

Table 1. Main findings on the incorporation of by-products into pasta production.

By-Product	By-Product Particle Size	Substitution or Addition (%)	Pasta Treatment	Major Ingredient	Type of Pasta	Technological Quality	Nutritional Quality	Sensory Quality	Ref.
Apple pomace	N.R.	Substitution: 10 to 50%	Extrusion. Drying: 40 °C for 8 h Final moisture: 12.5%	Wheat flour and eggs	Spaghetti	Color: N.R. OCT: N.R. Cooking quality: ↑WA Texture: ↓Hardness	↑Polyphenols, ↑Flavonoids, ↑Ash, ↓Protein, ↓Fat, ↑Dietary fiber (S and I)	N.R.	[52]
Apple peel powder	N.R.	Substitution: 10 and 15%	Extrusion. Drying: room T°—24 h	Durum wheat semolina	Fettuccine	Color: ↓L ↑b OCT: ↓Time (only in 15%) Cooking quality: ↑CL, ↑WA Texture: ↓Hardness, ↓Adhesiveness	↑Polyphenols ↑Antioxidant Capacity	Reduction of sensory quality (Panel: N = N.R.—Trained)	[53]
Banana peel	N.R.	Substitution: 5 and 10%	Lamination. Drying: 60 °C—1.5 h	Wheat flour and eggs	Fettuccini	Color: N.R. OCT: N.R. Cooking quality: ↑CL, =WA Texture: N.R.	↑Fat	No differences (Panel: N.R.)	[54]
Banana peel	N.R.	Substitution: 5%	Lamination. Drying: 50 °C—4 h	Corn and rice flour	N.R.	Color: No differences OCT: N.R. Cooking quality: N.R. Texture: No differences	N.R.	N.R.	[55]
Bergamot pomace flour	<0.8 mm	Substitution: 1.5 to 5%	Fresh.	Durum wheat flour	N.R.	Color: ↑L ↓a ↓b OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Polyphenols, ↑Flavonoids	Less acceptability (Panel: N = 18—Training: N.R.)	[56]
Blackcurrant pomace (two types: extruded and non- extruded)	N.R.	Substitution: 5 and 10%	Extruded. Pre-drying: 80 °C—30 min Drying: 40 °C—19.5 h	Durum wheat semolina	Tagliatelle	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: ↓WA, ↓SI (only in non-extruded type) Texture: ↑Hardness, ↑Work of cutting	↑Fat, ↑Ash, ↑Dietary fiber (S and I), ↑Antiradical activity	N.R.	[46]
Carrot and beetroot- apple pomace	340 µm	Substitution: 10 to 30%	Extrusion. Drying: N.R. Final moisture: 12%	Durum wheat semolina	Penne	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: ↑CL, ↑WA, ↑SI Texture: ↓Hardness (only in 30%)	↑Fiber (S, I and total)	Reduction of sensory quality, more in beetroot-apple pasta (Panel: N.R.)	[57]
Date, apple and pear by-products	1 mm	Substitution 2.5 to 10%	Lamination. Drying: 45 °C—Time: N.R. Final moisture: 13%	Wheat semolina	Pappardelle	Color: ↓L ↓a ↓b OCT: ↓Time Cooking quality: ↑CL, ↑WA Texture: N.R.	↑Fiber, ↑Ash, =Protein	Reduction of sensory quality (Panel: N.R.)	[58]
Enzyme treated kinnow pomace	<100 µm	Addition: 10 and 20%	Extrusion. Drying: 60 °C—Time: N.R. Final moisture: 5–6%	Durum wheat semolina	N.R.	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	N.R.	Highly acceptable (Panel: N = 10—Training: N.R.)	[59]
Fig peels	<500 µm	Substitution: 10 to 16%	Fresh	Durum wheat semolina	Tagliatelle	Color: N.R. OCT: N.R. Cooking quality: ↑CL, =WA, =SI Texture: N.R.	↑Polyphenols, ↑Antioxidant Capacity. In both analysis, clear differences at day 0, converge by day 12.	Initially better sensory quality in control pasta, but pasta with the by-product improves after day 3 (arbitrary quality evaluation) (Panel: N = 5—Trained)	[47]
Grape and olive pomace	N.R.	Addition: 3 to 7%	Extrusion. Drying: 40 °C—20 h	Durum wheat and eggs	Tagliatelle	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Polyphenols	N.R.	[60]
Grape marc extract	N.R.	Substitution of all the water	Extrusion. Pasteurization: 90 °C—3 min Drying: (1) 60 °C—20 min (2) 90 °C—130 min at 90 °C (3) 75 °C—50 min (4) 45 °C—160 min (5) 50 °C—1040 min	Durum wheat semolina	Spaghetti	Color: N.R. OCT: =Time Cooking quality: ↓CL, ↓WA, ↓SI Texture: =Hardness, ↑Adhesiveness	↑Flavonoids, ↑Polyphenols, ↑Antioxidant Capacity	No differences (Panel: N = 15—Trained)	[61]
Grape marc powder	811 µm	Addition: 2.5 to 7.5%	Extrusion. Fresh.	Wheat flour	Fettuccini	Color:↓L ↑a ↓b OCT: =Time Cooking quality: ↑CL (only in 5% and 7.5%), =WA Texture: N.R.	↑Polyphenols, ↑Antioxidant Capacity	Less acceptability (Panel: N.R.)	[62]
Grape pomace	200 μm	Substitution: 5 and 10%	Extrusion. Drying: 50 °C—TIME: N.R. Final moisture: 12%	Durum wheat semolina	Spaghetti	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: ↑CL, ↓SI Texture: ↑Hardness, ↓Adhesiveness	↑Polyphenols, ↑Antioxidant Capacity, ↓pGI, ↑SDS, ↓RDS	Loss of sensory quality in aroma, color, flavor, astringency, and granularity (Panel: N = N.R.—Trained)	[63]
Grape pomace	N.R.	Addition: 5 and 10%	Fresh.	Durum semolina	Tagliatelle	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Polyphenols, ↑Flavonoids	N.R.	[64]
Grape skins	N.R.	Substitution: 3 to 9%	Pasta processing: N.R. Pre-drying: 30–35 °C—TIME: N.R. Drying: 40–55 °C—TIME: N.R. Final moisture: 13%	Wheat flour and eggs	N.R	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Protein, ↑Antioxidant Capacity	Better sensory quality with substitution 3–6% (Panel: N = 10—Training N.R.)	[65]
Grape skins	<180 μm	Addition: 0 to 6%	Extrusion. Pre-drying: room T°—30 min Drying: (1) 60 °C—40 min (2) 80 °C—120 min (3) 40 °C—120 min	Wheat flour	Rigatoni	Color: N.R. OCT: N.R. Cooking quality: ↑CL Texture: ↑Hardness	↑Fiber, ↑Polyphenols, ↑Antioxidant Capacity, ↑RS	N.R.	[66]
Grape skins	<180 μm	Addition: 0 to 6%	Extrusion. Drying: (1) 20 °C—30 min (2) 40 °C—60 min (3) 80 °C—120 min (4) 40 °C—120 min	Wheat flour	Rigatoni	Color: ↓L OCT: N.R. Cooking quality: N.R. Texture: =Hardness, ↓Gumminess	↑Fiber, ↑Polyphenols, ↑RS	N.R.	[67]
Grape skins	<180 μm	Addition: 0 to 6%	Extrusion. Drying: (1) room T°—30 min (2) 40 °C—60 min (3) 80 °C—120 min (4) 40 °C—120 min	Wheat flour	Rigatoni	Color: ↓L ↑a ↓b OCT: N.R. Cooking quality: ↑CL, =WA Texture: ↑Hardness	↑Ash, ↑Fat, ↑Fiber, ↑Polyphenols, ↑RS	N.R.	[68]
Grape skins	<180 μm	Addition: 0 to 6%	Extrusion. Drying: (1) room T°—30 min (2) 40 °C—60 min (3) 80 °C—120 min (4) 40 °C—120 min	Wheat flour	Rigatoni	Color: N.R. OCT: N.R. Cooking quality: ↑CL Texture: ↑Hardness	↑Fiber, ↑Polyphenols, ↑RS	N.R.	[69]
Olive oil by-product	N.R.	Addition: 10 and 15% (with transglutaminase (TG) tested only at 10%: 0, 0.3, 0.6%)	Extrusion. Pasteurization: 90 °C—3 min Drying: (1) 60 °C—20 min (2) 90 °C—130 min at 90 °C (3) 75 °C—50 min (4) 45 °C—160 min (5) 50 °C—1040 min	Durum wheat semolina	Spaghetti	Color: N.R. OCT: ↓Time, =Time (with TG) Cooking quality: ↑CL, ↓SI, ↑WA (=with TG) Texture: ↑Hardness (=with TG)	↑Flavonoids, ↑Carotenoids, ↑Polyphenols	Reduction of sensory quality (improved by adding TG) (Panel: N = 15—Trained)	[70]
Olive pomace	200 μm	Substitution: 5 and 10%	Extrusion. Drying: 50 °C—TIME: N.R. Final moisture: 11%	Durum wheat semolina	Spaghetti	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: ↑CL, ↑WA, ↑SI Texture: ↑Hardness, ↑Adhesiveness	↑Polyphenols, ↑Antioxidant Capacity, ↑Fiber, ↑RS, ↑RDS, ↑SDS	N.R.	[71]
Olive pomace	N.R.	Substitution: 7.5%	Handmade. Drying: 50 °C—5 h	Wheat flour	Laces	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Polyphenols, ↑Flavonoids, ↑Antioxidant Capacity, ↑Ash, =Protein, ↑Fat, ↑Dietary fiber (S and I), ↑Vitamin E	Less acceptability (Panel: N = 71—Untrained)	[72]
Orange fibre	<125 µm	Addition: 2.5 to 7.5%	Fresh.	Wheat flour	Fettuccini	Color: No trend in L, a, b. OCT: N.R. Cooking quality: ↑CL, ↑WA Texture: N.R.	↓Protein, ↑Fat, ↑Ash, ↑Fiber (Total and I), ↑Carotenoids, ↑Polyphenols	Reduction of the overall sensory quality with 5% (Panel: N = 50—Untrained)	[73]
Orange pomace and cucumber peel powder	<0.250 mm	Addition: 5 to 20%	Extrusion. Drying: 50 °C—4 h	Durum wheat semolina	Tubular shape	Color: ↓L ↑a, ↑b with orange pomace ↓a, =b with cucumber peel OCT: ↑Time Cooking quality: ↑CL, ↑SI Texture: ↑Hardness	↓Protein, ↓Fat, ↑Ash, ↑Fiber (S and I), ↑Carotenoids, ↑Chlorophyll, ↑Polyphenols, ↑Antioxidant Capacity	N.R.	[49]
Raspberry pomace	300 µm	Substitution: 3.7 to 12%	Extrusion. Drying: 42–55 °C—28 h. Final moisture 12.5%.	Durum wheat semolina	Tubular shape	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: ↑CL, ↓WA, ↓SI (only in ≥10%). Texture: N.R.	N.R.	Lower hardness and less acceptability (Panel: N.R.)	[74]
Watermelon rind powder	250 µm	Addition: 5 to 15%	Fresh.	Wheat semolina	Noodles	Color: L no trend, ↓a ↑b OCT: N.R. Cooking quality: ↓CL, ↑WA Texture: ↓Hardness, ↓Adhesiveness	N.R.	No trend (Panel: N = 30—Semi-trained)	[75]
Watermelon rind powder	<400, 210 and 149 μm	Substitution: 10%	Extrusion. Drying: 50 °C—5 h	Durum wheat semolina	N.R.	Color: ↓L ↑a ↑b OCT: ↓Time Cooking quality: ↓WA, ↓SI, ↑CL Texture: ↑Hardness, ↑Adhesivity	↑Polyphenols, ↑Flavonoids, ↑Ash, = Protein, ↑Fat, ↑Dietary fiber (S and I), ↑Antioxidant Capacity, ↓pGI	No differences in acceptability. (Panel: N = 60—Untrained)	[51]
Artichoke by-product extract	400–500 μm	Addition: 10%	Fresh.	Wheat flour, durum wheat semolina and eggs	Fettuccine	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: N.R. Texture: N.R.	↑Total Phenolics	N.R.	[76]
Black cumin cake	N.R.	Substitution: 5 to 25%	Extrusion. Drying: 9 steps from 35 °C to 55 °C—Total time 7 h	Durum wheat semolina	Tagliatelle	Color: N.R. OCT: No trend Cooking quality: ↑CL, SI: No trend Texture: No trend	↑Protein, ↑Fat, ↑Ash, ↑Fiber (S and I), ↑pGI, ↑Minerals, ↑Polyphenols, ↑Flavonoids, ↑Antioxidant Capacity	N.R.	[77]
Broccoli roots and leaves, pomegranate peels and olive pomace	<500 µm	Addition: pomegranate peels and olive pomace 3 and 6%—broccoli roots 10%	Fresh.	Durum wheat semolina	Tagliatelle	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Polyphenols,↑Flavonoids, ↑Antioxidant Capacity	Better acceptability (Panel: N = 7—Trained, Acceptability not valid)	[78]
Brocoli leaf powder	≤0.60 mm	Addition: 2.5 and 5%	Fresh.	Durum wheat semolina	Penne	Color: ↓L ↓a ↑b OCT: No trend Cooking quality: ↑SI Texture: ↓Hardness	↑Ash, ↑Fat, =Protein	Changes in attributes and volatiles (Panel: N = N.R.—Trained)	[79]
Carrot pomace	N.R.	Substitution: 2 to 10%	Extrusion. Drying: 60 °C—3 h Final moisture: 8%	Durum wheat semolina	Cut Ziti	Color: ↓L ↑a ↑b OCT: N.R. Cooking quality: ↑CL, ↓WA Texture: ↓Hardness	N.R.	N.R.	[80]
Carrot pomace	≤125 µm	Addition: 10 and 20%	Extrusion. Drying: 55 °C—2 h Final moisture: 12%	Wheat flour with and without eggs	Noodles	Color: N.R. OCT: N.R. Cooking quality: ↑CL, =WA Texture: N.R.	↑Protein, ↑Fat, ↑Ash, ↑Fiber, ↑Carotenoids	High acceptability is indicated but no data is shown comparing the samples (Panel: N.R.)	[81]
Cashew apple pomace	<210 µm	Substitution: 5 to 20%	Extrusion. Drying: 50 °C—8 h Final moisture: 13%	Durum wheat semolina	Spaghetti	Color: ↓L ↑a ↑b OCT: ↓Time Cooking quality: ↑CL, ↓SI, ↓WA Texture: ↑Hardness, ↑Adhesiveness, ↓Springiness, ↓Cohesiveness, ↓Gumminess, ↓Chewiness, ↓Elongation rate, ↑Tensile strength	↓Protein, ↓Starch, ↑Fat, ↑Ash, ↑Fiber (S and I), ↑Polyphenols, ↑Antioxidant Capacity	Less acceptability (from 10%) (Panel: N = 60—Untrained)	[82]
Celery root and sugar beet by-products	270–500 µm	Substitution: 5 to 20%	Extrusion. Drying: 25 °C—3 days.	Wheat flour	N.R.	Color: N.R. OCT: ↓Time (particularly in celery root pasta) Cooking quality: ↑CL, ↑WA Texture: N.R.	N.R.	Reduction of sensory quality (Panel: N = 11—Trained)	[83]
Cucumber pomace	N.R.	Substitution: 2 to 10%	Fresh.	Wheat flour and eggs	Noodle	Color: ↓L ↑a ↓b OCT: N.R. Cooking quality: N.R. Texture: N.R.	↓Protein, ↑Fat, ↑Fiber, ↑Ash, ↑Minerals, ↑Antioxidant Capacity	Minor changes (Panel: N.R.)	[84]
Hazelnut skin (≠varieties)	500 µm	Substitution: 5 to 15%	Fresh.	Wheat flour and eggs	Tagliatelle	Color: ↓L ↑a ↓b OCT: N.R. Cooking quality: N.R. Texture: Differences by variety	↓Protein, ↑Fat, ↑Ash, ↑Fiber (S and I), ↑Polyphenols, ↑Antioxidant Capacity	Less acceptability (Panel: N = 82—Untrained)	[48]
Hibiscus sabdariffa by-product	270 µm	Substitution: 10 to 20%	Fresh.	Wheat flour and eggs	Fettuccine	Color: ↓L ↑a ↓b OCT: N.R. Cooking quality: N.R. Texture: ↓Hardness	↓Protein, ↑Fiber (S and I), ↑Minerals, ↑ Vitamin C, ↑Polyphenols, ↓Vitamin B	N.R.	[85]
Juice, puree, and pomace from red cabbage and spinach	N.R.	Substitution: 1 to 10%	Extrusion. Drying: N.R.	Durum wheat semolina	Spaghetti	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Polyphenols, ↑Fiber (S and I), ↑Antioxidant Capacity, ↑β-Carotenoids (Spinach pasta), ↓pGI	N.R.	[86]
Juice, puree, and pomace from red cabbage and spinach	N.R.	Substitution: 1 to 10%	Extrusion. Drying: N.R.	Semolina	Spaghetti	Color: ↓L ↓a ↓b (spinach pasta)—↓L ↑a ↓b (red cabbage pasta) OCT: ↓Time (only in 10%) Cooking quality: ↑CL, ↓WA (only in high %) Texture: ↑Hardness (spinach pasta), ↓Hardness (red cabbage pasta)	↑Protein (Cysteine) (Spinach pasta), ↑Ash	N.R.	[87]
Onion skin powder	<0.5 mm	Substitution: 2.5 to 7.5%	Extrusion. Drying: 35–55 °C—TIME: N.R..	Durum wheat semolina	N.R.	Color: ↓L ↑a ↓b (in cooked pasta) OCT: ↓Time Cooking quality: ↑CL, ↑SI in 2.5–5% and ↓SI in 7.5% Texture: N.R.	↓Fat, ↑Ash, ↑Fiber (S and I), ↑Flavonoids, ↑Polyphenols, ↑Antioxidant Capacity, =Protein	Reduction of sensory quality (Panel: N = N.R.—Trained)	[88]
Pennywort pomace	210 µm	Substitution: 5 to 20%	Extrusion. Drying: 50 °C—TIME: N.R. Final moisture: 9-11%	Durum wheat semolina	Spaghetti	Color: ↓L ↓a ↑b OCT: ↓Time Cooking quality: ↑CL, ↓SI, ↓WA Texture: ↑Hardness, ↓Cohesiveness, ↑Gumminess, ↑Chewiness, ↓Elongation rate, ↓Tensile strength	↑Protein, ↑Fat, ↑Lipids, ↑Ash, ↑Fiber (S and I), ↑Polyphenols, ↑Antioxidant Capacity, ↓Starch	Less acceptability (Panel: N = 60—Untrained)	[89]
Potato peel	40, 70, 145, 219 and 250 µm	Substitution: 2 to 15%	Extrusion. Drying: 80 °C—2 h	Wholegrain wheat flour	Spaghetti	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: ↑CL, ↓MII Texture: ↑Hardness	↑Fiber (S and I)	Less acceptability (Panel: N.R.)	[50]
Red chicory by-product powder	<0.2 mm	Substitution: 5 to 15%	Fresh.	Durum wheat semolina	Spaghetti	Color: ↓L ↑a ↓b OCT: ↑Time Cooking quality: ↑CL, ↓SI Texture: ↑Hardness ↑ Adhesivity	↑Polyphenols, ↑Antioxidant Capacity	Descriptive analysis: More bitterness and less uniform color. (Panel: N = 12—Trained)	[90]
Red potato pulp and cherry pomace	N.R.	Substitution: 10 to 30%	Extrusion. Drying: 40 °C—30 h Final moisture: 12.5%	Wheat flour and eggs	N.R.	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: ↑WA Texture: ↓Hardness (red potato pulp pasta), =Hardness (cherry pomace pasta)	↑Polyphenols, ↑Ash, ↑Dietary fiber (S and I)	N.R.	[91]
Sesame (Sesamum indicum L.) oil cake	N.R.	Addition: 5 and 15%	Lamination. Pre-drying: 56–59 °C—50 min Drying: (1) 70 °C—10 min (2) 30 °C—360 min. Final moisture: 12.5%	Wheat semolina	Lasagna	Color: N.R. OCT: N.R. Cooking quality: ↑WA, ↑CL (with lower %), =WA, =CL (with higher %) Texture: N.R.	↑Ash, ↑Protein, ↑Fat, ↑Crude fiber	Less acceptability (Panel: 5—Trained, Acceptability not valid)	[92]
Tomato by-product	N.R.	Substitution: 10 and 15%	Pasta processing: N.R. Pre-drying: 30–35 °C—TIME: N.R. Drying: 40–55 °C—TIME: N.R. Final moisture: 13%	Wholegrain durum wheat semolina	Spaghetti	Color: N.R. OCT: ↓Time Cooking quality: ↑CL, ↓WA Texture: ↑Hardness	↓Protein, ↑Fiber (S and I), ↑Lycopene, ↑Carotenoids	Reduction of sensory quality (Panel: N = 15—Trained)	[93]
Tomato by-product, linseed meal	N.R.	Substitution: 10 and 15%	Extrusion. Drying: 60 °C—17 h	Rice flour and fava bean flour	Gluten Free macaroni	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: ↓Fracturability (tomate pomace pasta), =Fracturability (linseed meal pasta)	↑Polyphenols, ↑Flavonoids, ↑Antioxidant Capacity, ↑Tocols, ↑Carotenoids (Tomato pasta), ↓Carotenoids (Linseed Meal pasta), ↑Fiber, ↑Ash, ↑Lipids, ↑Protein (Linseed meal pasta)	N.R.	[31]
Beer debittered trub	<200 µm	Substitution: 0 to 15%	Fresh.	Durum wheat semolina	Spaghetti	Color: ↓L ↑a ↓b OCT: ↓Time (only in 15%) Cooking quality: ↑CL, ↓SI (=SI only in 15%) Texture: ↑Hardness, ↑Adhesiveness (=Adhesiveness only in 15%)	↑Fat, ↑Protein, ↑Ash, ↑Fiber, ↓Starch, ↓In Vitro Starch Digestibility	Best sensory quality in 10%, worst in 15% (Panel: N = 20—Trained)	[94]
Brewer’s spent grain	≤700 µm	Substitution: 5 to 20%	Extrusion. Drying: 58 °C—18 h Final moisture: 12.5%	Durum wheat semolina	Spaghetti	Color: ↓L ↑a ↓b OCT:↓Time (only in 20%) Cooking quality: ↓WA Texture: ↓Hardness	↑Fiber, =Protein, ↑Ash, ↑β-Glucans, ↑Antioxidant Capacity, ↑RS	Lower sensory quality, less stickiness and hardness (Panel: N = 3—Trained)	[95]
Brewer’s spent grain	<500 µm	Addition: 3 to 25%	Fresh.	Durum wheat semolina, wheat flour and eggs	Lasagna	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: ↓Hardness	N.R.	N.R.	[96]
Brewer’s spent grain (two types: BSGE (einkorn)—BSGT (tritordeum))	≤700 µm	Substitution: 5 and 10%	Extrusion. Drying: 58 °C—18 h Final moisture: 12.5%	Durum wheat semolina	Macaroni	Color: N.R. OCT: ↑Time Cooking quality: ↑CL, ↑WA Texture: N.R.	↑Protein, ↑Fiber, ↑Ash, ↑β-Glucans, ↑Antioxidant Capacity	Lower sensory quality, less stickiness and hardness (Panel: N = 3—Trained)	[97]
Brewer’s spent grain (two types: EverVita Pro (EVP)— EverVita Fibra (EVF))	EVP: 52 µm EVF: 320 µm	Addition: EVP 10 to 20% EVF 5 to 10%	Extrusion. Drying: <80 °C—22 h	Durum wheat semolina	Spaghetti	Color: ↓L ↑a ↓b OCT: ↓Time Cooking quality: N.R. Texture: No trend	↑Protein, ↑Fiber, ↑Ash, ↑Fat, ↑Arabinoxylans	Slight improvement in appearance, color, and smell, but worsening of taste (Panel: N = 7—Trained)	[98]
Grape marc, brewer’s spent grain and maize marc	≤250 µm grape marc and brewer’s spent and ≤220 µm maize bran	Addition: 2.5–15% (plus 17.5 and 20% only for maize bran)	Extrusion. Drying: (1) 60 °C—20 min (2) 90 °C—130 min (3) 75 °C—150 min (4) 45 °C—160 min (5) 50 °C time—1040 min.	Durum wheat semolina	Spaghetti	Color: N.R. OCT: N.R. Cooking quality: N.R. Texture: N.R.	↑Polyphenols, ↓ACH (Maize Bran pasta)	Reduction of the overall sensory quality (Panel: N = 10—Trained)	[99]
Malt whisky spent grain	200 µm	Addition: 5 to 20%	Extrusion. Drying: 40 °C—6 h	Spelt flour	Spelt macaroni	Color: ↑Color chroma OCT: N.R. Cooking quality: ↑CL Texture: ↑Hardness, ↓Cohesiveness, ↓Fracturability	↑Protein, ↑Fiber, ↑Polyphenols, ↑Antioxidant Capacity	N.R.	[100]

Explanations: Not Reported, N.R.; Optimum Cooking Time, OCT; Water Absorption, WA; Swelling Index, SI; cooking loss, CL; Soluble, S; Insoluble, I; Transglutaminase, TG; Mass Increase Index, MII; Resistant Starch, RS; Rapidly Digested Stach, RDS; Slow Digested Stach, SDS; Predicted Glycemic Index, pGI; Available Carbohydrate Content, ACH.

. Only two articles analyze the influence of particle size. Namir et al. [50] investigate this in potato peels, and although they find differences in various pasta parameters, these differences are not very significant. However, it is important to note that all the by-products used had a particle size smaller than 250 microns. On the other hand, Long et al. [51], studying the incorporation of watermelon rind powder with particle sizes less than 400, 210, and 149 microns, observed that as the particle size of the by-product decreased, the differences between the enriched pasta and the control were minimized. This highlights the great importance of this parameter, which is often not indicated, and in some cases, by-products with a much higher particle size compared to the semolina or flours used for pasta production are utilized.

3.2. Culinary Quality

The effects of incorporating fruit and vegetable waste ingredients into pasta will be determined by their components. Some of these components will impart a certain color to the final product, while others will have a greater impact on its culinary characteristics. In general, these by-products are high in fiber, primarily cellulose.

Studies on fiber enrichment in pasta have mainly focused on in vitro digestibility analysis and fibers such as resistant starch, inulin, or oat bran [101,102,103,104]. Soluble fibers strengthen the gluten network or the starch-gluten-fiber matrix, reducing solid losses during cooking and slowing sugar release during in vitro starch digestion. In contrast, insoluble fibers like cellulose interfere with the formation of the gluten network and increase sugar release during digestion [102,104]. The results showing a reduction in the predicted glycemic index with soluble fibers align with those found by Foschia et al. [103], although these researchers also identified antagonistic effects when different types of fibers were combined. Therefore, predicting the effects of incorporating fiber-rich by-products is challenging, as the outcome depends on both the fiber content and the type of fiber and its combinations.

It should also be noted that there are few studies on the effects of cellulose, one of the main fibers present in fruit and vegetable waste, or its impact on pasta quality. The only study analyzing the inclusion of a cellulose-rich fiber, such as pea fiber, found minimal changes in the texture or culinary quality of pasta (spaghetti) at inclusion levels up to 12.5%, but it did not assess factors such as the form or size of this type of fiber [104]. On the other hand, a fiber with a high water absorption capacity, such as guar gum, results in lower cooking losses, pasta with higher moisture content, a softer and stickier texture, and less elasticity, although these effects depend on the amount added.

3.2.1. Cooking Time

Table 1 shows the main results from studies on the inclusion of various by-products in pasta production. When evaluating the influence of by-product incorporation in pasta production, these differences also become evident. The observed differences can be attributed to various factors, such as the type of fiber and its water absorption capacity, the amount of by-product incorporated, the pasta shape, whether it is dried or fresh pasta, or the level of hydration used during production. Regarding optimal cooking times, the results show considerable consistency, generally indicating a reduction in cooking times when by-products in powder form are incorporated or no significant effect is observed, with few exceptions [49,90,97]. The optimal cooking time is determined visually by pressing the cooked pasta between two glass plates at different times until the appearance of a whitish central area, indicating ungelatinized starch, disappears. In general, the inclusion of by-products interferes with the gluten network, facilitating water penetration into the starch, thus reducing cooking times. This effect is less pronounced in fresh pasta than in dried pasta, as cooking times for fresh pasta are significantly shorter. This explains why some studies on fresh pasta do not detect significant differences in cooking time [62,79] or observe changes only at the highest incorporation levels [53,87]. However, the presence of a small amount of water or fibers with a high water retention capacity that compete with starch for water, could delay the optimal cooking time. For example, in the study by Kaur et al. [49], the inclusion of orange pomace and cucumber peel, by-products that may contain high amounts of water-absorbing fibers like pectins, is analyzed. In this study, the amount of water used in pasta production is not specified, so we must assume it is the same in all cases. In the study by Nocente et al. [97], the moisture content is adjusted according to the by-product incorporated (brewer’s spent grain from einkorn or tritordeum), but it is not indicated on what basis this moisture content is modified. The same amount of water is used for pasta production with different levels of brewer’s spent grain. This study does not provide an explanation for the increase in cooking times. Interestingly, another study by the same group on barley brewer’s spent grain found no changes in optimal cooking times or observed a reduction at higher percentages (20%) [95]. This reduction is explained by interference with the gluten network and better water absorption by the starch. In this case, dough hydration was increased as more by-product was incorporated.

3.2.2. Swelling, Water Absorption, and Weight Loss Index

In general, pasta containing by-products tends to show greater weight loss during cooking, with only two exceptions [61,75]. However, the observed differences in swelling index and water absorption are not as clear, and there are significant variations across the studies analyzed.

Weight loss during cooking occurs due to the release of soluble components from the pasta (starch and other non-starch polysaccharides) into the cooking water. In traditional pasta, most of this loss corresponds to the release of starch. Starch granules are embedded in the gluten network, and if this network weakens, starch can escape to the outside. In pasta incorporating by-products, two phenomena may contribute to this weight loss. First, the total wheat protein content decreases due to a dilution effect, and second, by-product particles interfere with the gluten network, weakening it. This weakening is well observed when analyzing the microstructure of pasta, as shown in some of the cited studies [58,63,71]. In the study by Ho and Dahri [75], unlike most studies, weight loss decreased as the content of by-products (watermelon rind powder) increased. However, in this case, the pasta produced was “wet noodle”, which is not dried, made with wheat flour instead of semolina, and includes kansui (sodium silicate and sodium carbonate), which alters the dough pH and thus the gluten network configuration. The article does not provide a clear explanation for the reduced cooking losses compared to other studies. It is known that using flour instead of semolina results in pasta with different characteristics, where starch granules tend to be less embedded in the gluten matrix [105], which could increase weight loss in the control. However, further investigation into the effect of dough pH on these outcomes is needed.

In studies involving grape by-products, a contradiction seems to exist. While Iuga and Mironeasa [69] observed increased weight loss due to these by-products, which they attributed to the interactions of the by-product’s polymers with the gluten matrix and/or protein competition for water, Marinelli et al. [61] reported a reduction in weight loss. They attributed this to the ability of antioxidant components in grape pomace extract to form complexes with proteins around the starch granules, encapsulating them during cooking and limiting excessive swelling and amylose diffusion.

The studies analyze the solid content of the cooking liquid but not its composition. This could be relevant, as the loss of starch is different from the loss of nutritionally important components, such as polyphenols.

To reduce cooking losses, which may result from gluten network weakening, strengthening the gluten network could be attempted. For example, Padalino et al. [70] achieved reduced weight loss and increased optimal cooking time by introducing transglutaminase into the formulation. This enzyme is capable of linking lysine and glutamine groups, strengthening the protein network. However, its application also increases the hardness of the pasta, which was already harder due to the by-product incorporation. In other gluten-dependent products, gluten is often added, or oxidative enzymes and additives are used to strengthen the gluten network [7]. However, these aspects have not been extensively studied in pasta production with by-products.

Regarding cooking yield, swelling index, and water absorption of cooked pasta (grams of water per gram of dry pasta), as mentioned, the results are less consistent. Both parameters are determined according to the procedure described by Padalino et al. [106] and tend to follow the same trend (i.e., if the swelling index increases, water absorption also increases). Water absorption depends on the amount of water absorbed by starch and wheat proteins. Therefore, if some of the starch has passed into the cooking water, it is logical for the water absorption by the pasta to decrease during cooking. However, if the incorporated by-product has a high water retention capacity, it may compensate for or even reverse this trend. As a result, water absorption outcomes will largely depend on the water absorption capacity of the by-product. For example, Padalino et al. [93] observed that when a tomato processing by-product was included, water absorption during cooking decreased. However, this could be increased by incorporating hydrocolloids with a high water absorption capacity, such as xanthan or guar gum. Nevertheless, this incorporation did not reduce cooking losses, which are more related to gluten network deterioration, and increased the hardness of the pasta.

It is also necessary to consider dough hydration since higher dough hydration results in lower water absorption during cooking. Studies that adjust dough hydration based on the water absorption capacity of the incorporated by-product observe lower water absorption during cooking compared to those that do not adjust hydration. The main issue is that most studies that modify dough hydration do not specify the exact criterion for the changes they make, and there is no clear measure to indicate the basis for these modifications beyond the experience or observations of those making the pasta. This is an area that should be improved in such studies. This is particularly important in fresh pasta, although dried pasta undergoes dehydration before cooking. In these cases, the problem is that most studies do not report the final moisture content of the pasta. A drying time and temperature are typically provided, along with a maximum moisture content, usually between 12% and 12.5%. However, it is unlikely that all types of pasta will reach the same final moisture content with the same treatment, as it tends to be higher in pasta containing ingredients that retain water better or when hydration is increased. For example, while Nocente et al. [95] increased the water content of the dough based on the water absorption capacity of the incorporated by-product and observed a reduction in water absorption, Simonato et al. [71], who did not adjust the hydration, observed higher water absorption. However, this is not always the case, and Gumul et al. [52], who did increase dough hydration when incorporating by-products, observed an increased final absorption in those cases. In general, explanations for these effects are not provided, and in most cases, the results are compared to other studies with similar outcomes, without addressing contradictions with those reporting opposite results.

3.2.3. Texture

As with water absorption, there are also significant differences in the texture of pasta with added by-products. Some authors attribute a reduction in pasta firmness to interferences in, and the weakening of, the gluten network [58]. However, other authors who observe the same weakening of the gluten network report opposite results, with an increase in firmness [63,71]. Unfortunately, as with water absorption, the explanations for these phenomena are often limited to comparisons with previous studies that align with their findings. Since there are prior studies with differing results, it is always possible to compare with one that matches the observations of each study.

To identify potential explanations for the reported results, we can focus on the method used to measure pasta texture. In some studies, a compression test is conducted by placing the pasta perpendicular (vertically) to the instrument [63,71], while in others, it is placed horizontally [93]. In some cases, the orientation or compression distance is not specified [79], and in others, a cutting test is performed [46,49,52,95]. However, even though these differences make it difficult to compare studies, there is also no consistency when the same measurement method is used or even with the same type of pasta.

Another possible explanation for these differences may lie in the type of by-product incorporated and its composition, particularly regarding the type of fiber it contains. As mentioned earlier, Tudorică et al. [104] observed different trends when incorporating different types of fiber. Unfortunately, most studies do not characterize the fibers in the by-products beyond categorizing them as soluble or insoluble in some cases, nor do they describe their functional properties. More in-depth studies on the influence of different types of fibers present in by-products, such as cellulose, pectins, and others, would be valuable for gaining a better understanding of their effects.

3.2.4. Color

During pasta cooking, temperatures typically stay below 100 °C. If temperatures approach this threshold, they generally remain at that level for no more than 10 min. Therefore, Maillard reactions or sugar caramelization, which could be responsible for color changes, do not occur. As a result, the final color of the pasta comes from the color of its ingredients. In fact, when analyzed, the same effect on color is usually observed in both uncooked dried pasta and cooked pasta [63,71]. Thus, while there is generally agreement that the incorporation of by-products reduces the lightness (L) of the pasta due to the darker colors of the by-products compared to the flour or semolina used, changes in the values of a* and b* vary in each case. The a* value represents the green-red axis (negative values indicate greener tones, while positive values indicate redder tones), whereas the b* value corresponds to the blue-yellow axis (negative values indicate bluer tones, while positive values indicate yellower tones). When a by-product with higher a* and b* values than semolina is added, the pasta exhibits the same tendencies. However, when the by-product has values closer to those of semolina, no such differences are observed [49]. Similarly, when a by-product with highly negative a* values and high positive b* values is introduced, the pasta tends to increase its negative a* and positive b* values [79]. However, not all studies characterize the color of the raw materials, which would help to better explain the results obtained.

3.3. Nutritional Quality

As shown in Table 1, most studies on pasta enrichment with fruit and vegetable by-products include the analysis of some of their nutritional components. It is well known that these by-products contain a high amount of fiber and bioactive compounds such as polyphenols or carotenoids [107,108]. In fact, most research has focused on these compounds. The observed results are quite clear, with almost all studies reporting an increase in fiber content, both soluble and insoluble, as well as polyphenolic substances and carotenoids. This is expected, as pasta production should not significantly alter the fiber content. The process typically involves mixing and kneading the ingredients, followed by shaping through cold extrusion or lamination, and drying at low temperatures (below 100 °C). Furthermore, as mentioned previously, when fruit and vegetable by-products are incorporated into pasta, most studies report greater solid loss during cooking. However, the composition of these lost solids is rarely analyzed, even though they may contain bioactive compounds and soluble fiber. Regardless, enriching pasta with nutrient-rich ingredients still results in a higher overall nutrient content in the final product. Even if some components are lost to the cooking water, the majority remain in the pasta.

In addition to fiber and phenolic compounds, pasta with by-products also tends to be richer in ash (mineral substances) and fat, as shown in Table 1. This is partly due to the composition of the by-products used and partly due to the low content of these nutrients in the semolina or flours used for pasta production (refined flours, as they have their bran and germ removed, leaving only the endosperm). The results regarding protein content are less consistent, which is due to the varying protein content of the different by-products used. However, in general, by-products with higher protein content than flour or semolina increase the final protein content of the pasta, and vice versa. Obviously, these increases or decreases are less pronounced in fresh pasta than in dried pasta, due to the higher water content in fresh pasta compared to dried pasta, and the diluting effect of the other components unless expressed on a dry basis. A similar phenomenon occurs when comparing dry pasta and cooked pasta.

Another nutritionally relevant factor is the antioxidant capacity of the resulting pasta. This capacity can be measured in various ways, as reflected in the different studies incorporating these analyses. In general, pasta enriched with fruit and vegetable by-products exhibits higher antioxidant capacity. This is quite logical, as bioactive compounds such as polyphenols, carotenoids, or flavonoids present in by-products, and which remain in the pasta after processing, have a high antioxidant potential [109,110].

It has also been shown that the inclusion of by-products generates pasta with a lower predicted glycemic index or reduced starch digestibility [63,71,77,86,94]. It is important to note that the inclusion of by-products reduces the starch content in the final pasta, leading to lower glucose release since this comes from starch. However, if results are expressed based on total starch, it is also logical, as numerous polyphenols have been shown to reduce the glycemic index by inhibiting digestive enzymes like amylases and through their interaction with starch [111]. Furthermore, the presence of polyphenols in some by-products may help regulate appetite and induce satiety via the gut-brain axis and gut homeostasis [112]. Additionally, the presence of certain hydrocolloids, found in some by-products, such as pectins or beta-glucans, also helps slow starch digestibility. This effect is due both to increased viscosity and to a potential inhibitory action on enzyme activity or reduced enzyme accessibility to starch [113]. Finally, the presence of insoluble fibers, such as cellulose, may also contribute to this effect, as it has been shown to affect postprandial blood sugar regulation [114]. Nevertheless, all studies conducted on pasta with by-products have been performed in vitro, and no in vivo studies have been conducted to confirm the results obtained in these preliminary assays, nor to explore the mechanisms behind this reduction in greater depth.

3.4. Antimicrobial Activity

It is known that many fruit and vegetable by-products, especially their extracts, have some antimicrobial activity, particularly against pathogenic bacteria, which is linked to the presence of certain components [115]. In fact, this characteristic has been used for their reintroduction into the food chain to extend the shelf life of various food products [116]. In most cases, pasta is a product that is sold with low moisture and low water activity, meaning that microbial growth does not usually pose a problem for its preservation. However, fresh pasta is also commercially available. This type of pasta, with high water activity, is produced in specialized facilities under appropriate temperature control and must be stored under refrigeration to extend its shelf life, often being packaged in modified atmospheres. In this case, it is beneficial to minimize microbial growth.

Studies on the antimicrobial activity of some by-products and the effect of their inclusion in pasta formulations to extend shelf life have focused on fresh pasta. Positive results have been found with mixtures of broccoli by-products with olive oil pomace and pomegranate peels [78], fig peels [47], cucumber pomace [84], grape pomace [64], and an extract of phenolic compounds from artichoke by-products [76]. In some of these studies, a slight but statistically significant increase in acidity [84] or a decrease in pH [47,78] has been observed. These modifications could help reduce microbial growth and thus increase the shelf life of the pasta, but they do not fully explain the observed effect, which is generally stronger against bacteria than against molds and yeasts. This effect could be attributed to some antimicrobial component, as it is known that such compounds exist in fruits and vegetables. However, these have not been identified or quantified in the studies conducted.

3.5. Acceptability

Acceptability is one of the most concerning aspects when developing products enriched with by-products. It has been shown that one of the main reasons for consumer rejection of these products is their lower organoleptic quality. Unfortunately, most studies on pasta enriched with by-products do not conduct acceptability studies. In the studies that do include acceptability tests, the number of panelists rarely exceeds 60 people, which is somewhat low for this type of research [117]. In general, studies that include sensory analysis report a decrease in the overall quality of pasta enriched with by-products, as well as lower acceptability. In terms of acceptability, some studies highlight the different colors and appearance of the pasta, but also its inferior taste. It is worth noting that people tend to have a negative predisposition toward bitter flavors [118], and the phenolic compounds, which we have already mentioned are abundant in both by-products and enriched pasta, often contribute to these flavors [119].

Despite the importance of these findings for the potential commercialization of these products, very few studies address ways to improve their acceptability. It is also worth mentioning that, while most studies on pasta quality assess plain, unseasoned cooked pasta, which follows a well-established methodology, sensory acceptability studies often use pasta prepared with different seasonings. While most studies do not incorporate any kind of dressing [58,82,84], which is uncommon when pasta is consumed, some use commercial sauces [73], which could influence the results. However, no study has analyzed the impact of these seasonings or cooking methods on product acceptability. It is known that certain bitter flavors can be masked by specific molecules [120], which could improve acceptability and help these products reach the market. Similarly, bitter flavors can be masked using physical methods [121], although this has not been studied in pasta production.

Furthermore, some changes in the culinary quality of the pasta, such as modifications in texture, can lead to lower acceptability, and this should be examined to explore possible ways to improve it.

4. Challenges in the Industrial Application of By-Product Enriched Pasta

The first issue or challenge associated with these applications is the need to obtain a regular and homogeneous product, in sufficient quantities and throughout the year, for an industry to consider producing this type of product. Regarding consistency, although few studies have analyzed it, there are usually significant differences between fruit varieties or the prior processing of certain by-products. For example, Zeppa et al. [48] showed that the composition of hazelnut skins from different varieties differed, and these variations affected the quality of the pasta in which they were incorporated. Similarly, Gaita et al. [65] observed discrepancies in the polyphenol content of different grape skins depending on the grape variety. It is also possible to treat these by-products to obtain distinct fractions with variations in macronutrient content, which will differently affect the quality of the resulting pasta [98]. Furthermore, no studies have evaluated the effect of prior processing of by-products on the quality of the pasta produced, but factors such as particle size or drying conditions may have an impact. It is well known that the particle size of semolina is a key factor in the quality of the resulting pasta [34], so it is reasonable to assume that this would also apply to ingredients derived from by-products. This has already been demonstrated in other applications, such as cookies or cakes [7]. However, in the case of pasta, it has been scarcely studied, although the limited studies available indicate a significant influence of this factor.

The cost of these by-products is also an aspect to consider, although it is rarely addressed in scientific publications. Even if by-products are available at minimal cost, it must be considered that those with high moisture content must be dried quickly to extend their shelf life and ground to the appropriate particle size. Both processes involve costs, which, along with logistical costs, must be factored in. Additionally, these processes have environmental impacts, such as carbon footprint, which should be assessed through life cycle analysis or other techniques to verify their environmental viability [122].

The need to have these by-products available regularly throughout the year will depend on each case. Some by-products, such as brewer’s spent grain, are produced year-round and would pose no supply issues. Other by-products generated during specific months of the year can be safely stored once dried and ground. However, many of them lose organoleptic characteristics with prolonged storage. In such cases, seasonal production can be implemented as a sales strategy.

5. Conclusions and Future Studies

The incorporation of plant-based by-products into pasta production offers significant nutritional advantages, particularly by increasing fiber content and bioactive compounds such as polyphenols and carotenoids. However, this inclusion alters the culinary quality of the pasta, generally reducing optimal cooking times, increasing cooking losses, modifying water absorption during cooking, and darkening the color of the pasta, thereby changing its hue. The main drawback of these incorporations is a decrease in the organoleptic quality of the pasta, particularly leading to lower consumer acceptability. Obviously, these effects, both negative and positive, are less pronounced when the amount of by-product incorporated is reduced.

Most studies conducted to date have focused on analyzing the impact of by-product incorporation on pasta quality. However, no studies have examined various factors of interest related to these effects. It would be useful to investigate how pre-processing treatments of the by-products, such as drying and especially milling (and thus particle size), influence the quality and acceptability of the resulting pasta. Likewise, it would be beneficial to explore how pasta quality can be improved through adjustments in formulation and processing when by-products are included. Although some studies have addressed this topic through methods such as enzymatic reinforcement of the gluten network [70] or the incorporation of gums [93], these are scarce, and further research is needed. Additionally, studies aimed at improving the acceptability of the resulting pasta through its final cooking methods, including the use of sauces or other seasonings, should not be overlooked.