Chapter 8
Agroindustrial Coproducts as Sources of Novel Functional Ingredients
Maria Lourdes Pérez-Chabela
Annel M. Hernández-Alcántara Autonomous Metropolitan University, Iztapalapa, Mexico City, Mexico
Abstract
The disposal of agroindustrial coproducts derived from fruit and vegetable processing represents a serious contamination problem. Fruit and vegetable peels contain important bioactive ingredients like fiber and antioxidants. Different fiber sources contain high amounts of soluble and insoluble fiber. The peel fiber can be employed as a prebiotic ingredient. In vitro studies have demonstrated that the flour of these peels stimulates the growth of probiotic lactic acid bacteria, besides the production of an important amount of short chain fatty acids, mainly butyric. In same manner, these fibers as coating material improved the resistance of lactic acid bacteria against bile and acidic conditions. These fruit peels are low-cost potential food functional ingredients that develop novel functional foods that improve nutritional quality.
Keywords
coproducts
bioactive ingredients
fiber
antioxidants
polyphenols
prebiotic
1. Agroindustrial Coproducts
According to the Food and Agriculture Organization (FAO) one-third of the edible parts of food produced for human consumption gets lost or wasted globally. This amount accounts about 1.3 billion tons per year (FAO, 2011). Food coproducts are residues of high organics load, which are usually derived during postharvest handling or storage. Coproducts of fruit processing exist in large amounts, the commercial production of fruit fibers is limited to small amounts. They are used in the feed industry. Fresh fruit tissue after squeezing is not stable against enzymatic degradation and is very sensitive to microbiological spoilage, a drying process soon after fruit processing is necessary (Fisher, 2012). In developing countries more than 40% of the food losses occur at postharvest and processing levels, while in industrialized countries, more than 40% of the food losses occur at retail and consumer levels.
Fruit and vegetable processing is the most investigated substrate for the extraction of several types of antioxidants and dietary fibers (DFs). Phenols and carotenoids could be applied as natural food, because they extend the shelf life of the product by delaying the formation of off-flavors and rancidity (Galanakis, 2012).
2. Dietary Fiber From Agroindustrial Coproducts
Many agricultural coproducts are rich in DFs. The term dietary fiber refers to the remnants of edible plant cells, polysaccharides, lignin, and associated substances resistant to digestion by human alimentary enzymes (Trowell, 1974). In 2001, the American Association of Cereal Chemists (AACC, 2001) defined the fiber dietary as: “the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plant substances. Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation.” DF should be obtained through consumption of foods. In addition to fiber, minimally processed fruits, vegetables, grains, and legumes provide micronutrients that are essential components of healthful diets. Recommendations for DF intake for adults generally fall in the range of 20–35 g/day or 10–13 g DF/1000 kcal (Marlett and Slavin, 1997). DF is one of the main dietary factors contributing to the well-being of consumers. Reyes-Caudillo et al. (2008) studied the DF content present in Mexican chia (Salvia hispanica L.) they reported a 37%–40% of total DF, concluding that chia seeds are an important source of DF.
Borrelli et al. (2004) studied the possibility of using the roasted coffee silvers (the coffee silver skin is a tegument of coffee beans that constitutes a by-product of the roasting procedure) dietetic fiber rich. The results of their investigation showed that this material has 60% total dietetic fiber with a relevant component (14%) of soluble dietetic fiber. Nawirska and Uklanska (2008) determined and compared the neutral DF (NDF) and acid DF (ADF) contents in the pomace from the processing of two apple varieties (Idared and Champion), two strawberry varieties (Ducat and Kent), chokeberry, black currant, red cabbage, and two carrot varieties (Black carrot and Dolanka). Chokeberry pomace was found to contain the largest, and Dolanka carrot pomace the smallest amounts of NDF and ADF. The results imply that chokeberry pomace, black currant pomace, and strawberry (both Ducat and Kent) pomace should be recommended as best suited for the production of high DF food components. Aguedo et al. (2012) studied the composition of by-products from cooked fruit processing (apple and pear pomaces), the content of DF is from 70% the dry-weight with an insignificant soluble fraction, by-products came from cooked fruit implies that they contain specific aroms and sensory characteristics. Table 8.1 shows some agroindustrial coproducts and their percentage of DF.
Table 8.1
| Sources | Total Dietary Fiber | References |
|---|---|---|
| Fig | 16.53 | Sánchez-Zapata et al. (2012) |
Banana Chía seeds |
32.9–51.9 a 37–40 |
|
| Lemon albedo | 22 | Fernández-Ginés et al. (2004) |
| Raspberry pomace | 77.5 | Górecka et al. (2010) |
Cactus pear peel Pineapple peel Guava powder Apple marc |
64.15 62.54 46.72 70.91 |
|
| Maguey leaf b | 41.44 | Castillejos-Gómez et al. (2015) |
| Orange peel | 38.11 | Pérez-Chabela et al. (2015a,b) |
a Depending of the varieties of banana.
b Residue from“barbacoa” elaboration. Barbacoa is a Mexican dish elaborated with lamb meat, where the maguey leaves are utilized to retain and transfer heat to meat.
2.1. Classification and Composition
DF can be classified as polysaccharides type, divided into three major fractions (Schneeman, 1986):
- • Structural polysaccharides (cellulose, hemicellulose, and some pectin)
- • Structural nonpolysaccharides (lignin)
- • Nonstructural polysaccharides (gums and mucilage)
But the most widely accepted and used system of classification is on the basis of solubility and/or the fermentation behavior in an in vitro system using an enzyme component, which simulates digestion.
According to their water solubility, DF is conventionally classified into (Esposito et al., 2005):
- • Insoluble DF (IDF)/less fermented fiber and soluble dietary fiber (SDF)/well-fermented fibers. Insoluble fiber consists of cellulose, part of hemicellulose and lignin
- • Soluble fiber consists of pectin, gums, and mucilage
Soluble fiber is that fraction of the total fiber that is suspended in water during analysis. SDF may vary 15%–50% of the total fiber using different analytic methods. Nearly all fiber-containing foods have more insoluble than soluble dietary fiber. About two-thirds to three-fourths of the DF in typical mixed-food diets is water insoluble (Marlett, 1997).
2.1.1. Cellulose
Cellulose consists of long unbranched chains of glucose, (1-4) a linked d-glucopyranose. Cellulose is found in abundance in nature in virtually all plant tissues and is therefore a common component of our diet. Dietary cellulose is not digested in the stomach and small intestine, and 85% are recoverable in ileostomy contents from subjects fed diets containing usually eaten foods (Cummings, 1984). Cellulose is fermented in the large intestine by the microflora producing short chain fatty acids (SCFA), hydrogen, carbon dioxide, and methane.
2.1.2. Hemicellulose
Hemicellulose are constituted by pentose sugars: arabinose and xylose, and many of the arabinoxylans have a high water-holding capacity, a property that would explain the increase the rate food residue passes through the gut (Holloway et al., 1980). Arabinoxylans are a major component of DF in whole grains, having considerable inclusions in both the endosperm and bran. During normal wheat flour processing, a majority of the arabinoxylans is removed as a by-product. In the gastrointestinal tract, arabinoxylans acts much like a soluble fiber being rapidly fermented by the microflora of the colon (Lattimer and Haub, 2010).
2.1.3. Pectins
Pectic substances are a complex group of polysaccharides in which d-galacturonic acid is a principal constituent. They are structural components of plant cell walls and also act as intercellular cementing substances. The backbone structure of pectin is an unbranched chain of axial-axial-(1-4)-linked d-galacturonic acid units. Long chains of galacturonan are interrupted by blocks of l-rhamnose-rich units that result in bends in the molecule. Pectin is highly water-soluble and is almost completely metabolized by colonic bacteria (Kay, 1982). The additives are selected from high-methoxyl varieties, which have higher gelling properties. Amidation also improves the gelling capacity, and amidated pectin is used in low-sugar jams and as emulsifiers and stabilizers (Southgate, 2001).
2.1.4. Lignin
Lignin can be described as branched networks built up by phenylpropane units. Lignin is partly linked to cell wall cellulose and noncellulosic polysaccharides and serves in principle two main functions. Lignin bond and anchor the cellulose microfibrils and other matrix polysaccharides and in this way stiffens the walls thus preventing biochemical degradation and physical damage of the walls (Bach Knudsen, 1997).
2.1.5. Mucilage and gums
The mucilage is synthesized by plant secretory cells, prevent desiccation of seed endosperm your use in food industry as hydrophilic, stabilizer, for example, guar. The gums are secreted at the site of plant injury by specialized secretory cells, your use in food and pharmaceutical (Kay, 1982). Several exudative gums are used as additives and food ingredients. The most widely used gums are the galactomannan gums, guar, and carob bean gums, which are used as thickness in soup and other foods (Southgate, 2001).
2.2. Physiological Effects From the DF
Large amounts of research have reported an inverse relationship between fiber consumption and the risk for coronary heart disease and several types of cancer. For that reason, the FDA has adopted and published the claim that increased consumption of DF can reduce the prevalence of coronary heart diseases and cancer. The mechanisms behind these findings are still unclear. However, it is attributed to several factors, including increasing bile acid excretion, decreased caloric intake, increased SCFA production, carcinogen binding effects, increased antioxidants, and increased vitamins and minerals. Although not as yet adopted by the FDA, DF is suggested to play a role in other conditions, such as obesity and diabetes (Lattimer and Haub, 2010). Fig. 8.1 shows the physiological effects of DF, and following physiological effects are attributed to DF (Howlett et al., 2012):
- • Reduced blood total and/or cholesterol levels
- • Attenuation of postprandial glycemia/insulinemia
- • Reduced blood pressure (BP)
- • Increased fecal bulk/laxation
- • Decreased transit time
- • Increased colonic fermentation/SCFA production
Figure 8.1 The Physiological Effects of Dietary Fiber.
2.2.1. Lowering cholesterol levels
Fibers may be fermented in the colon into SCFA, such as acetate, propionate, and butyrate. Propionate has been shown to inhibit the activity of the enzyme hydroxy-3-methylglutaryl-CoA reductase, the limiting enzyme for cholesterol synthesis. DF has the ability to bind with bile acids and prevents their reabsorption in the liver, and thus inhibiting cholesterol synthesis (Chen et al., 1984). Many studies have shown a positive relationship between diets rich in SDFs, such as β-glucan (βG) from oats and barley, pectin from fruits, guar gum, and psyllium, and reduced serum total cholesterol and low-density lipoprotein cholesterol (LDL-C) (Gunness and Gidley, 2010). Babio et al. (2010) examined the effect of different types and sources of DF on body weight, glucose metabolism, and lipid profile. They concluded that clinical studies consistently show that the intake of viscous DF decreases the LDL-cholesterol levels.
2.2.2. Postprandial plasma glucose and glycemic attenuation
Soluble fiber forms gels in the gastrointestinal tract, and may decrease the absorption of glucose and cholesterol from the intestinal lumen (Kaczmarczyk et al., 2012). Fujii et al. (2013) demonstrated that the increased of DF intake was associated with better glycemic control and more favorable risk factors, including hypertension, metabolic syndrome, and CKD, along with improvements in insulin sensitivity and microinflammation, diabetic patients should be encouraged to consume more DF in daily life according to the ethnic foods. The protective effect may result from the ability of fiber to lower postprandial glucose peak, which leads to decreased insulin demand and protects the pancreas from exhaustion (Verma and Banerjee, 2010).
2.2.3. Reduce blood pressure
Elevated BP is a modifiable major risk factor for cardiovascular morbidity. Pettersen et al. (2012) reported that the diet affects measured BP levels, both systolic and diastolic, with vegans and lacto-ovo vegetarians having lower BP than nonvegetarians. People may benefit from a diet containing more plant foods to prevent hypertension. Sánchez-Muniz (2012) speculated that fiber could influence cardiac input/output and total peripheral resistance by affecting the sympathetic and parasympathetic nervous systems, but data concerning the effects of DFs on BP are scarcer and little is known regarding the mechanisms involved at the present time.
2.2.4. Bulking ability
DF affects bowel function by increasing fecal volume and weight, improving stool consistency, decreasing transit time, and increasing stool frequency (Raninen et al., 2011). The fermentation of DF can be increase the mass bacterial due to the growth and proliferation of bacteria (Slavin, 2013). Insoluble fibers, such as cellulose and lignin, are mostly unfermentable by colonic microflora and increase fecal bulk by their particle formation and water-holding capacity (Elleuch et al., 2011). Wheat bran is among the best bulking agents. Some fermentable hemicellulose fibers, including cabbage, increase fecal bulk by increasing fecal flora. In contrast, highly fermentable fibers, such as pectin, have little effect on fecal bulk (Mudgil and Barak, 2013).
2.2.5. Fermentation on intestine (increase colonic fermentation)
At both the colonic and systemic levels, fermentation and especially SCFA production play an integral role. Colonic epithelial cells preferentially use butyrate as an energy source, even when competing substrates, such as glucose and glutamine, are available. Butyrate is considered a key nutrient determining the metabolic activity and growth of colonocytes and may function as a primary protective factor against colonic disorders, although data on this topic are conflicting. SCFAs are water soluble and are absorbed into the blood stream (Lupton, 2004).
2.3. Fiber Effect in Foods
DF is naturally present in cereals, fruits, vegetables, and nuts. During processing the foods undergo various physical, chemical, enzymatic, and thermal treatments, which directly or indirectly affect the composition of total fiber. Incorporation of fiber can change the consistency, texture, rheological behavior, and sensory attributes of the end products. The addition of fiber in breakfast cereals, bread, cookies, cakes, yogurt, beverages, and meat products has been reported with favorable results. Fiber can even be produced from sources that might otherwise be considered waste products, like agroindustrials coproducts. For example, wheat straw, soy hulls, oat hulls, peanut and almond skins, corn stalks and cobs, spent brewer’s grain and unedible portions of fruits (peel mainly), and vegetables resulted in large quantities of raw matter that can be converted into fiber ingredients, which may be highly functional in certain food applications (Dhingra et al., 2012).
Nonetheless, in other food the fiber content is poor, mainly in animal origin foods considered as the main source of protein in diet. Incorporation of fiber from agroindustrial coproducts is a way to enrich the nutritional composition of foods, where these ingredients can act as extenders of texture modifiers.
2.3.1. Meat products
Meat is an integral component in our diet. Meat is a major source of food proteins with high biological value, an excellent source of some essential fats, soluble vitamins, and minerals. But recently, negative campaigns about muscle foods, and their possible health hazard effects, show that consumers are increasingly interested about health-oriented functional meat products. Functional meat products either possess nutritional ingredients that improve health or contain lesser quantity of harmful compounds like cholesterol, fat (Biswas et al., 2011). Fernández-Ginés et al. (2004) studied the effect of the addition of lemon albedo in bologna sausages; they utilized two types of albedo: raw and cooked. The addition of albedo to bologna sausages represents a good source of fiber dietary and may have beneficial effects, possibly due to the presence of active compounds that induce a decrease in residual nitrite levels. The use of orange fiber was studied in salchichón (Spanish dry-fermented sausage). Orange fiber decreases residual nitrite levels and favors micrococcus growth. Both effects have a positive impact on sausage safety and quality. The reduction in residual nitrite decreases the risk of nitrosamine formation (Fernández-López et al., 2008). Cava et al. (2012) evaluated the incorporation of three DF (tomato, beet root, and inulin) in chopped cooked chicken products. The fiber incorporation reduces the pH of the chicken batters, increases the water-holding capacity, but the color and texture were affected. The tomato fiber increased the redness of the meat products. Sánchez-Zapata et al. (2013b) studied the effect of the incorporation of tiger nut in chorizo. “Chorizo” is the most popular dry-cured meat product in Spain. Tiger nut addition decreases fat and increases moisture and fiber content; there were slight changes in the physicochemical properties. The addition of tiger nut fiber to Spanish dry-cured sausages provides a healthier product: lesser percentage of fat and more total DF content. In the same manner, López-Vargas et al. (2014) determined the technological, nutritional, and sensory characteristics of pork burgers added with passion fruit albedo, obtained from passion fruit technology. The addition of this coproduct improves their fiber content, the cooking characteristics, and moisture retention. The passion fruit albedo can be recommended in pork burger production as a DF source. Díaz-Vela et al. (2015) evaluated the integration of agroindustrial coproducts as food ingredients: cactus pear (Opuntia ficus I.) flour and pineapple (Ananas comosus) as fiber source in cooked sausages, the use of fruit peel flour improved the physicochemical properties of the cooked sausages. Both types of flour increased water retention, increased yield, and decreased oxidative rancidity in cooked sausages. Fruit peels could be employed as a source of bioactive compounds. Pérez-Chabela et al. (2015b) determined the effect the orange peel flour, potato starch, and carrageenan, employing a mixture design approach on physicochemical and textural properties of sausages, fiber in orange peel flour increased moisture, water retention, texture, and decreased oxidative rancidity. Cooked meat products conditions (temperature and ionic strength) affected the functionality of meat extenders like potato starch and carrageenan, indicating that orange peel flour as a cheap and viable fiber source can replace more expensive meat extenders, as potato starch and carrageenan. Verma et al. (2015) investigated the efficacy of sweet potato powder and water as a fat replacer in low-fat pork patties. Results concluded that low-fat pork patties with acceptable sensory attributes, improved cooking yield, and textural attributes can be successfully developed with the incorporation of a combination of 1.0% sweet potato powder and 9.0% chilled water. Hence, the developed product can be marketed as a functional meat product with improved processing and sensory characteristics.
The DF can improve the health beneficiary characteristics and the consumer acceptance of meat products added with it. The cholesterol-reducing property of DF is being utilized by meat processors to attract the health-conscious consumers worldwide. Various sensory attributes of processed meat products, such as texture, juiciness, and color are variably modified by the DF addition. The overall acceptance of the DF-added meat products has increased positively in recent time (Talukder, 2015). The incorporation of DFs, either soluble or insoluble, in the meat products is considered needed in view of their various health benefits.
2.3.2. Dairy products
Milk contains no fiber. Dairy products have recently come under fire from researchers showing the detrimental effects of saturated fat and cholesterol in the body. Researchers reported positive effects of fiber in the diet. Fortification of dairy products using natural resources (fruits, cereal, etc.) is one of the best ways to improve the overall nutrient intake of food with minimal side effects (Abou-Zeid, 2016). Fernández-García and Mcgregor (1997) evaluated the use of seven types of IDF from five different sources (soy, rice, oat, corn, and sugar beet) in yogurt. Fiber addition caused acceleration in the acidification rate of the experimental group yogurts, and most of the fortified yogurts also showed increases in their apparent viscosity. Soy and sugar beet fibers caused a significant decrease in viscosity due to partial syneresis. In general, fiber addition led to lower overall flavor and texture scores. The evolution of organic acids during the fermentation and cold storage of yogurts showed a similar pattern; only acetic and propionic acids were found in significantly higher amounts in the fiber-fortified product. Sendra et al. (2010) studied the effect of orange fiber addition on yogurt viscoelastic properties; orange fiber addition modifies yogurt rheological parameters that remained low fiber doses due to the disruptive effect of the fiber, where the presence of fiber particles always alters yogurt structure. Ramírez-Santiago et al. (2010) studied the syneresis, microstructure, and rheological properties of yogurt enrichment with SDF from Pachyrhizus erosus, an underutilized crop. Their results showed that the yogurt with P. erosus displayed a lower syneresis percent, more open and relaxed protein network, and lower elastic and viscous module, indicating the viability to obtain a commercial product. Staffolo et al. (2012) studied the effect of the interaction between nutrients and fibers (inulin, apple, bamboo) to evaluate the availability for absorption of glucose, calcium, and iron using yogurt as a food model. Results showed that the different plant fibers decreased glucose, calcium, and iron availabilities; these findings could be positive or negative depending on the nutrient and the nutritional stage or health of the population who would receive the food under study. Seckin and Baladura (2012) evaluated the effect of the addition of apple, bamboo, and wheat DFs on color, texture, and sensory properties of strained yogurt during cold storage. Depending on storage, the most changed textural parameter is consistency in bamboo, wheat and apple fibrous strained yogurt. L, a, and b values of apple fibrous strained yogurts were determined to be different in comparison with bamboo and wheat fibrous strained yogurts due to the structure of apple fiber. The type of DF caused statistically significant changes in color, texture values, and sensory evaluation scores. Apple fibrous strained yogurts were not preferred by panelists because of their ragged structure, dominant apple taste, and strong odor. Panelists found bamboo and wheat fiber strained yogurts acceptable. No difference between wheat and bamboo fiber addition was detected by the sensory panel. Panelists found bamboo and wheat fiber–strained yogurts acceptable. In the same manner, Awad et al. (2014) utilized lupine flours, in the elaboration of imitation processed cheese, processed cheese can be formulated using different types of cheese with different degrees of maturation, flavorings, emulsifying, salts, and/or several ingredients of nondairy components. Nondairy ingredients have been used in processed cheese for many dietary and economic reasons. All processed cheeses produced were sensory acceptable but an overall acceptability was lowered by incorporating lupine in the formula. Body and texture scores of processed cheese were the most affected by increasing lupine ratio in formula without significant difference up to 50% substitution of the cheese base.
Some special milk to special dietary requirements can be low fat, delactosed, and fortified with SDF. In processed dairy products, like cheese and yogurt, the fiber incorporation enhances texture besides to offer a fermentable substrate for lactic acid bacteria, where fiber acts as a prebiotic.
2.3.3. Cereal products
Cereal products are consumed daily by the majority of the populations. These products are rich in carbohydrates and may contribute to the obesity problem, although now there are enriched products that are a vehicle of DF into people diet. Górecka et al. (2010) studied the effort to use raspberry pomace, a by-product of food processing, in cookies. Raspberry pomace is sourced directly from a fruit-processing plant. The content of DF in raspberry pomace was higher. These by-products were found to be rich in cellulose and lignin, and their addition did not have negative influence on organoleptic characteristics of the product and was accepted by consumers. The substantial DF content of fruit by-products and, in particular, fruit seeds, should attract the interest of dieticians. Ajila et al. (2010) utilized the mango peel powder as a potential source of antioxidant and DF in macaroni. Mango peel is obtained during processing of mango products and is currently discarded and thus, causing environmental pollution. When the mango peel powder is added into macaroni, the total content of DF increased 8.6%–17.8%, but also increased the cooking loss and the firmness. Mango peel can be utilized for the preparations of macaroni with improved nutritional properties. In another study, Lópes-Almeida et al. (2013) studied the effects of adding different DF sources (wheat bran resistant starch and locust bean gum) on process and quality parameters of pan bread. Wheat bran was the only fiber source that influenced specific volume and crumb chroma and hue angle. Wheat bran and locust bean gum contributed to retaining moisture in the crumb during the whole storage period. The acceptance of crust color, crust appearance, aroma, and taste was not affected by the addition of the different DF. Silva de Paula et al. (2013) characterized cereal bars with high levels of fiber and ω-3 using 0%, 5%, 10%, and 20% of linseed. Linseed is an oleaginous that has been used in the human diet for thousands of years, presents proteins with an amino acid composition that is similar to soy, and is considered a seed with good protein quality among vegetable origin products. This oleaginous is also rich in DF and the α-linolenic acid (ω-3) concentration in linseed is more than 50% its lipid content. Their results showed that the calorie value of the cereal bars were around 100 kcal/portion. The formulations containing linseed presented higher acceptability, and that with 20% of linseed was found to be the formulation with the best chemical and sensory characteristics. Therefore, the addition of linseed in cereal bars is a good option to develop a functional product, which may contribute to a healthy diet and to the reduction of several noncommunicable diseases. Total DF and the soluble and insoluble fractions increased as the amount of added linseed was higher and the caloric value was similar among the cereal bars.
Wandee et al. (2014) evaluated the use of Cassava pulp and pomelo peel for their potential as sources of DF in dried rice noodles. They demonstrated the potential of using fiber-rich fractions derived from agricultural product processing to improve qualities and to increase the total DF content of rice noodles. A combination of cassava pulp and pomelo peel gave the best results. Noodles made from combinations of these fiber sources contained about three times higher total DF content and displayed comparable textural properties and much higher cooking weight, as compared to the control. A mixture designed from three components (rice flour, cassava pulp, and pomelo peel) might be used as a tool to optimize composition and to obtain better noodle quality.
Cereal could be the main source of fiber in the diet, but in the last century processing eliminated most of the fiber for refined flours. The tendency now is to produce integral flours with part of the endosperm and other parts of the seed, especially in wheat. Other cereals can be processed more integrally, leaving important parts of the fiber in the flours. However, compared with agroindustrial coproducts from fruits and vegetables, cereal fiber as a coproduct is more expensive.
2.4. Fiber Effect In Vivo
Paturi et al. (2012) evaluated the gastrointestinal transit in 120 Sprague-Dawley rats fed DFs (inulin, potato fiber, maize starch, and cellulose as control). Fermentation of DF in the large intestine results in the production of short-chain fatty acids—predominantly acetic, butyric, and propionic acids. The results showed that rats fed diets supplemented with inulin, potato fiber, or maize starch resulted in higher cecal SCFA concentrations compared to rats fed cellulose diet. Pascoal et al. (2013) investigated the fermentation effects on the cecum of 16 Wistar rats treated with diets containing onion (source of fructans). The diet supplement with onion showed an increase in the production of total and individual (propionate, acetate, and butyrate) SCFAs and a decrease in the pH of the cecal content compared to control. Pérez-Chabela et al. (2015a) studied the physiological effects of agroindustrial coproducts (O. ficus) pear peel and stripe apple (Malus domestica) marc in 24 Wistar rats using inulin as control. Results showed that diets with coproducts result in higher average body weight gain, reduce glucose and triglycerides in serum, and higher nondigestible carbohydrates, apple marc showed similar physiological effects as compared to inulin for it can be employed as a good prebiotic source.
2.5. Short History of the Methods of Analysis of Dietary Fiber
Van Soest (1963) reported the first method for the determination of fiber and lignin using detergent. They evaluated the capacity of cetyltrimethylammonium bromide to dissolve proteins in acid solution. This method was called acid-detergent fiber method, which is not only a fiber determination in itself but also the major preparatory step in the determination of lignin. Prosky et al. (1985) determined the total DF content of food and food products using a combination of enzymatic and gravimetric procedures. Theander et al. (1994) reported the Uppsala methodology for rapid analysis and characterization of total DF (defined as the sum of DF polysaccharides and Klason lignin) utilizing a thermostable amylase and amyloglucosidase, method. The Official Method AOAC is the 992.16 Total Dietary Fiber Enzymatic–Gravimetric Method is applicable to determine the total DF in cereals, beans, vegetables, and fruits (AOAC, 2005).
3. Phenolic Compounds in Agroindustrial Coproducts
Phenolic compounds are ubiquitous in plants, and when plant foods are consumed, these phytochemicals contribute to the intake of natural antioxidants in the human diets. Agroindustrial by-products are good sources of phenolic compounds, and have been explored as a source of natural antioxidants (Balasundram et al., 2006). The polyphenols are secondary plant metabolites and have an important role in the defense system of the plant, protecting it from biotic and abiotic stress. Phenolic compounds also show antimicrobial activity against plant pathogens. Because of their biological role in plants, secondary metabolites are located primarily in the outer layers of fruits and vegetables and in the seeds. During processing, these plant parts are usually removed by peeling or are retained in the press residues (Kosseva, 2013). Table 8.2 shows some agroindustrial coproducts and their phenolic content.
Table 8.2
| Sources | Polyphenols (mg GAE/g) | References |
|---|---|---|
| Banana peel | 43.2 | Bezuneh and Kebede (2015) |
| Papaya peel | 26.6 | Bezuneh and Kebede (2015) |
| Fig | 5.72 | Sánchez-Zapata et al. (2012) |
| Guava powder | 44.04 | Verma et al. (2013) |
| Apple marc | 27.54 | Cerda-Tapia et al. (2015) |
| Orange | 12.30 | Al-Juhaimi (2014) |
| Lemon | 9.838 | Al-Juhaimi (2014) |
| Mandarin | 10.49 | Al-Juhaimi (2014) |
GAE, Gallic acid equivalent.
3.1. Classification and Composition
With more than 8000 structural variants, they are secondary metabolites of plants and denote many substances with aromatic rings bearing one or more hydroxyl moieties (Han et al., 2007). Polyphenols have been classified by their source of origin, biological function, and chemical structure. Also, the majority of polyphenols in plants exist as glycosides with different sugar units, and acylated sugars at different positions of the polyphenol skeletons. To simplify the discussion, classification of polyphenols in this review is done according to the chemical structures of the aglycones (Tsao, 2010).
3.1.1. Flavonoids
The name derives from the Latin “flavus,” which means “yellow.” Apart from their physiological roles in plants, flavonoids are important components of the human diet, although they are not considered as nutrients (Prochazkova et al., 2011). Flavonoids are the most abundant polyphenols in human diets, and are mainly divided into: (1) anthocyanins, glycosylated derivative of anthocyanidin, present in colorful flowers and fruits; (2) anthoxanthins, a group of colorless compounds further divided in several categories, including flavones, flavans, flavonols, flavanols, isoflavones, and their glycosides. Flavonols are mainly represented by myricetin, fisetin, quercetin, and kaempferol (Han et al., 2007). Flavonoids are uses as antioxidants, a term that is commonly used and can be defined in multiple ways according to the methods to measure their concentration. The in vitro flavonoid antioxidant activity depends on the arrangement of functional groups on its core structure. Both the configuration and total number of hydroxyl groups substantially influence the mechanism of the antioxidant activity (Heim et al., 2002).
3.1.2. Flavonols
Flavonols have a double bond between C2 and C3, with a hydroxyl group in the C3-position. They represent the most ubiquitous flavonoids in foods, with quercetin as the more representative compound. The main sources of flavonols are onions (up to 1.2 g/kg fresh wt.), curly kale, leeks, broccoli, and blueberries (D’Archivio et al., 2007). The biosynthesis of flavonols is a photosynthetic process, so these compounds are mainly located in the outer and aerial tissue of fruits (Quiñones et al., 2012).
3.1.3. Flavones
Flavones and their 3-hydroxy derivatives flavonols, including their glycosides, methoxides, and other acylated products on all three rings, make this the largest subgroup among all polyphenols. The skin of fruits contains large amounts of polymethoxylathed flavones, like in the skin of mandarin which content is up to 6.5 g/L of essential oil of mandarin (Tsao, 2010).
3.1.4. Flavanones
Flavanones comprise a minority group in food, although they appear at high concentrations in tomatoes and citrus, and in certain aromatic plants, such as mint. The main aglycones are naringenin in grapefruit, hesperetin in oranges, and eriodictyol in lemons. Orange juices contain 470–761 mg/L of hesperidin and 20–86 mg/L of narirutin (Leuzzi et al., 2000). Flavanones are located mostly in the solid parts of the fruit, particularly the white spongy portion, albedo, and the membranes separating the segments of the fruit), therefore, its concentration is up to five times higher in the fruits than in juices (Quiñones et al., 2012).
3.1.5. Isoflavones
Isoflavones have structural similarities to estrogens, hydroxyl groups in the C7 and C4 positions, like estradiol molecule. Isoflavones can bind to estrogen receptors and are classified thus as phytoestrogens. They are contained almost exclusively in leguminous plants, with soya and its processed products as the major source of these compounds, which contain the three main molecules (genistein, daidzein, and glycitein) that occur as algycones or more often as glucose-conjugated forms (Quiñones et al., 2012). Soybeans contain between 140 and 1530 mg isoflavones/kg fresh wt., and soy milk may contain between 12 and 130 mg/L (D’Archivio et al., 2007). Isoflavones are sensitive to heat and are often hydrolyzed to glycosides during industrial processing and storage, like in the production of soy milk.
3.1.6. Anthocyanidins
Anthocyanidins are water-soluble pigments, responsible for most of the red, blue, and purple colors of fruits, vegetables, flowers, and other plant tissues or products (Mazza et al., 2004). Anthocyanidins are widely distributed in the human diet: they are found in red wine, certain varieties of cereals and vegetables, but they are more abundant in fruit. Food contents are generally proportional to color intensity reaching values up to 2–4 g/kg. Anthocyanins are found mainly in the skin, except for some red fruits (cherries and strawberries) in which they also are present in the flesh (D’Archivio et al., 2007).
3.1.7. Flavanols
Flavanols or flavan-3-ols are often commonly called catechins. Catechin is the isomer with trans configuration and epicatechin is the one with cis configuration. Flavanols are found in many fruits, particularly in the skins of grapes, apples, and blueberries (Tsao, 2010). Proanthocyanidins, also known as condensed tannins, are dimmers, oligomers, and polymers of catechins. Due to their wide range of structures and molecular weight, the content of proanthocyanidins in food is difficult to establish, as in the case of cider apples with a degree of polymerization between 4 and 11 (Guyot et al., 2001). Proanthocyanidins are responsible for the astringent character of fruit as in grapes, apples, berries as same as in beverage like wine, cider, tea, and beer, and for the bitterness of chocolate (Rasmussen et al., 2005).
3.1.8. Phenolic acids
Phenolic acids are composed of hydroxycinnamic and hydroxybenzoic acids. They are ubiquitous to plant material and sometimes present as esters and glycosides. They have antioxidant activity as chelators and free radical scavengers with special impact over hydroxyl and peroxyl radicals, superoxide anions, and peroxynitrites (Carocho and Ferreira, 2013). Fruits and vegetables contain many free phenolic acids (Chandrasekara and Shahidi, 2010). In grains and seeds (especially in the brand or hull) phenolic acids are found in the bound form (Adom and Liu, 2002). These acids can only be freed or hydrolyzed upon acid or alkaline hydrolysis, or by enzymes (Tsao, 2010).
3.1.9. Hydroxybenzoic acids
The hydroxybenzoic acids, such as gallic acid and protocatechuic acid, are found in very few plants eaten by humans. The hydroxycinnamic acids consist chiefly of coumaric, caffeic, and ferulic acid that are rarely found in the free form. The bound forms are glycosylated derivatives or esters of quinic, shikimic, or tartaric acid (D’Archivio et al., 2007). Hydroxycinnamic acids, the major hydroxycinnamic acid is caffeic acid, which occurs in foods mainly as an ester with quinic acid called chlorogenic acid (5-caffeoylquinic acid). Chlorogenic acid and caffeic acid are antioxidants in vitro and they might inhibit the formation of mutagenic and carcinogenic N-nitroso compounds for the inhibitory effect on the N-nitrosation reaction in vitro (Han et al., 2007).
3.1.10. Stilbenes
Stilbenes are a small family of plant secondary metabolites derived from the phenylpropanoid pathway, and produced in a number of unrelated plant species. These compounds have numerous implications in plant disease resistance and human health (Chong et al., 2009). Examples of common stilbenes isolated from grape wine (Vitis vinifera), pine (Pinus and Picea), peanut (Arachis hypogaea), and sourghum (Sorhum bicolor) (Parage et al., 2012). Resveratrol is one of the most extensively studied stilbenes and is involved with health benefits related with its cardiovascular, chemopreventive, antiobesity, antidiabetic, and neuroprotective properties (Reinisalo et al., 2015). Another interesting stilbene with potential health properties is pinosylvin (3,5-hydroxytrans-stilbene), mainly found in the heartwood of Pinus species and at high concentrations in bark waste, thus this stilbene may represent an inexpensive polyphenols with considerable potential for diverse health promoting applications (Jeong et al., 2013).
3.1.11. Phenolic alcohols
Tyrosol (4-hydroxyphenylethanol) and hydroxityrosol (3,4-dihydroxyphenyletanol) are the main phenolic alcohols that are present in extra virgin olive oil (40.2 and 3.8 mg/kg, respectively) (Cabrini et al., 2001). Tyrosol is also present in red and white wines and beer (Covas et al., 2003), meanwhile hydroxytyrosol is found in red wine but also produced in vivo after its ingestion (De La Torre et al., 2006).
3.1.12. Lignans
Lignans are bioactive, nonnutrient, noncaloric phenolic plant compounds that are found in highest concentration in flax and sesame seeds and in lower concentrations in grains, other seeds, fruits, and vegetables (Peterson et al., 2010). They produced by oxidative dimerization of two phenylpropane units, and are mostly present in nature in the free form, while their glycoside derivatives are only a minor form (D’Archivio et al., 2007). The plant lignans most commonly distributed in foods are lariciresinol, matairesinol, pinoresinol, and secoisolariciresinol (Smeds et al., 2007).
3.1.13. Polyphenolic amides
Some polyphenols may have N-containing functional substituents. Two such groups of polyphenolic amides are of significance for being the major components of common foods: capsaicinoids in chilli peppers (Davis et al., 2007). Capsaicinoids, such as capsaicin, are responsible for the hotness of the chilli peppers but have also been found to have strong antioxidant and antiinflamatory properties, as well as the ability to modulate the oxidative defense system in cells (Tsao, 2010).
3.2. Physiological Effect From Phenolic Compounds
Polyphenols are thought to be responsible for some of the health effects conferred by a diet rich in fruit and vegetables. Both the formation of bioactive polyphenol-derived metabolites and the modulation of colonic microbiota contribute to these health benefits. Polyphenols may influence several metabolic or signaling pathways involved in cardiovascular disease (CVD), chronic inflammation, bone, gut health, carcinogenesis, and many degenerative diseases (Bolca et al., 2013).
3.2.1. Antioxidant activity and protection against oxidative stress
Polyphenols are strong antioxidants that complement and add to the functions of antioxidant vitamins and enzymes as a defense against oxidative stress caused by excess reactive oxygen species (ROS). Although most of the evidence of the antioxidant activity of polyphenols is based on in vitro studies, increasing evidence indicates they may act in ways beyond the antioxidant functions in vivo (Tsao, 2010). Owing to the incomplete efficiency of our endogenous defense systems and the existence of some physiopathological situations (cigarette smoke, air pollutants, UV radiation, high polyunsaturated fatty acid diet, inflammation, ischemia/reperfusion, etc.) in which ROS are produced in excess and at the wrong time and place, dietary antioxidants are needed for diminishing the cumulative effects of oxidative damage (Pietta, 2000).
Polyphenols have been found to be strong antioxidants that can neutralize free radicals by donating an electron or hydrogen atom. Polyphenols suppress the generation of free radicals, thus reducing the rate of oxidation by inhibiting the formation of or deactivating the active species and precursors of free radicals (Rice-Evans et al., 1996). Poyphenols can also function as metal chelators. Chelation of transition metals, such as Fe2+ can directly reduce the rate of Fenton reaction, thus preventing oxidation caused by highly reactive hydroxyl radicals (Perron and Brumaghim, 2009). However, they do not act alone, it has been found that polyphenols can actually function as coantioxidant, and are involved in the regeneration of essential vitamins (Zhou et al., 2005).
3.2.2. Hypoglycemic effects on diabetes risk
The antidiabetic properties of some dietary polyphenols, suggest that dietary polyphenols could be one dietary therapy for the prevention and management of type 2 diabetes. Dietary polyphenols may inhibit α-amylase and α-glucosidase, inhibit glucose absorption, stimulate insulin secretion, and reduce hepatic glucose output (Kim et al., 2016). Hanhineva et al. (2010) suggest that polyphenols may suppress glucose release from the liver, and improve glucose uptake in peripheral tissues by modulating intracellular signaling.
3.2.3. Cardiovascular protective effects
The polyphenols could be serious candidates to explain the protective effects of plant-derived foods and beverages. Based on current studies, a general consensus has been achieved to sustain the hypothesis that the specific intake of foods and beverages containing relatively high concentrations of flavonoids may play a meaningful role in reducing CVD risk through an improvement in vascular function and a modulation of inflammation (Habauzit and Morand, 2012). Vasodilator effects are able to improve lipid profiles and attenuate the oxidation of LDL. In addition, they have clear antiinflammatory effects and can modulate apoptotic processes in the vascular endothelium (Quiñones et al., 2013). Some wines, grape juices, and grape skin extracts caused endothelium-dependent relaxations in aortic rings. Other studies confirmed that polyphenol-rich sources, such as extracts from red wines, green and black tea, and several plants caused endothelium-dependent relaxations in large arteries, arterioles, and veins that were prevented by competitive inhibitors of eNOS and guanylyl cyclase (Andriantsitohaina et al., 2012).
3.2.4. Neurodegenerative protective effects
Excess production of ROS in the brain has been implicated as a common underlying risk factor for the pathogenesis of a number of neurodegenerative disorders, including Alzheimer’s disease and Parkinson’s disease. The resveratrol is an antioxidant and antiinflammatory but also activated the sirtuin 1 (SIRT1) and vitagenes, which can prevent the deleterious effects triggered by oxidative stress (Sun et al., 2010). In the central nervous system, the oral administration of green tea polyphenols and flavonoid-related compounds has been shown to inhibit iron-induced lipid peroxide accumulation and age-related accumulation of neurotoxic lipid peroxides (Nie et al., 2002). Epigallocatechin gallate (EGCG) postponed the onset of neurological symptoms and prolonged life span in a mice model of amyotrophic lateral sclerosis. Long-term treatment with EGCG increased the life span and enhanced movement abilities in a transgenic Drosophila melanogaster model of postdoctoral studies (Ebrahimi and Schluesener, 2012).
3.2.5. Cancer protective effects
Cancer is a major health problem and the main cause of death worldwide, affecting millions of people. The number of deaths resulting from cancer increases from low- to high-income countries, although incidence of cancer is now increasing in less developed countries as they succeed in achieving lifestyles similar to those observed in developed countries (Siegel et al., 2012). The phenolic antioxidants are isolated from plants and plant-derived food, or commercially available (synthetic ones). The most commonly diagnosed cancers worldwide are lung (12.7%), breast (10.9%), colorectal (9.7%), and stomach (7.81%), among others (Roleira et al., 2015).
Huang et al. (2010) studied the antimetastatic effects of the synthetized hispolon (a phenolic compound of the mushroom Phellinus linteus) on a highly metastaic human liver carcinoma cell lines, as well as its mechanism of action. Their results suggest that this phenolic compound inhibit the metastasis of the cellular lines by different mechanism, mainly by inhibiting matrix metalloproteinase-2/9 and urokinase-plasminogen activator through the PI3 K/Akt and ERK signaling pathways. Many potential mechanisms have been proposed, including both antioxidant and prooxidant effects, but questions remain regarding the relevance of these mechanisms to cancer prevention (Lambert and Elias, 2010). Polyphenols may exert these anticancer effects via a variety of mechanisms, including removal of carcinogenic agents, modulation of cancer cell signaling, and cell cycle progression, promotion of apoptosis and modulation of enzymatic activities (Vauzour et al., 2010).
3.3. Phenolic Compounds in Foods
In same manner as fiber addition, the use of agroindustrial coproducts derived from fruit (like peels) represents as well an important source of bioactive ingredients like phenolic compounds, with several important biological functions, as described earlier. The incorporation of fibers or flours from fruit peels in the best way to improve nutritional value of animal origin foods, even if cereal products derived from no-pigmented seeds are poor in phenolic compounds content.
3.3.1. Meat products
Verma et al. (2013) explored the potential antioxidant and value functional value of guava (Psidium guajava L.) powder in sheep meat nuggets The results of this study exhibited that guava powder is a rich source of DF, most of which present in an insoluble form and also possesses great antioxidant potential, such as radical scavenging activity and ferric reducing antioxidant power. Guava powder is also a rich source of phenolic compounds (44.04 mg GAE/g). Incorporation of guava powder significantly affected the physicochemical properties of the products. The most significant effect of guava powder addition in sheep meat nuggets is enrichment of the products with DF and phenolic compounds. Guava powder improved the redness value of the product, thus its appearance. Incorporation of guava powder could protect cooked sheep meat nuggets against lipid oxidation during refrigerated storage. Incorporation of guava powder up to 1% level did not affect the product’s organoleptic attributes. Thus, guava powder can be used as a source of antioxidant DF in sheep meat nuggets without affecting their acceptability. Sánchez-Zapata et al. (2013a) evaluated the effect of the addition of tiger nut fiber in a dry-cured sausage. Tiger nut fiber increases oxidation stability, probably due to the contribution of the bioactive compounds with antioxidant properties. Castillejos-Gómez et al. (2015) utilized the maguey leaves (these are discarded after barbacoa elaboration) as fiber and antioxidant sources on physicochemical properties and oxidative rancidity of cooked pork sausages. Maguey leaf flour had no effect on physicochemical and textural properties of cooked sausages, but the lipid stability was notably improved by the incorporation of maguey leaf flours. Maguey leaf flour from barbacoa elaboration is a good source of antioxidant compounds, and its application to cooked meat products, such as sausages, can be compensated by employing another extender in the formulation.
One of the major advantages of incorporating phenolic compounds in meat products is to avoid the fatty acids oxidation. Most meat products had fat in their formulation, and this fat is responsible of texture and characteristic flavor. Retarding the development of rancidity during maturation or storage of meat products is important.
3.3.2. Dairy products
Sun-Waterhouse et al. (2012) studied the addition of polyphenols to yogurt to deliver the health benefits of polyphenols and also the probiotic effects of starter cultures. These compounds can be added via two approaches: prefermentation approach (adding polyphenols before fermentation as part of the yogurt ingredient mixing) or postfermentation approach (adding polyphenols after fermentation as a part of the usual practice for improving flavor and color agents). Their results showed that the polyphenols content affect the viscosity, storage modulus of yogurt, and other properties. The same authors in 2013 compared the effects of adding purified berry polyphenols PP (cyaniding-3-O-β-glucopyranoside-chloride, Cyanindin) or a blackcurrant PP extract (BPE) before or after fermentation on the chemical, rheological, and microbiological properties of drinking yogurts formulated with low- or high-methoxy (LM or HM) pectin. Results showed that the incorporation of BPE before fermentation led to the presence of small phenolic molecules (mainly phenolic acids) in the yogurt 3.5–3.9 times greater than added after fermentation. Fermentation also influenced the PP profiles of yogurt. Adding BPE and Cyanidin before fermentation affected the colony number and appearance of starter cultures, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, as well as the elastic property and viscosity of the resultant yogurts. Carocho et al. (2015) evaluated the incorporation of decocted extracts and dried chestnut flowers and lemon balm plants in “Serra da Estrela,” a Portuguese cheese produced from cattle milk, in order to functionalize and provide antioxidant activity to this product. The cheeses showed higher antioxidant activity, mainly by lipid peroxidation inhibition. It was also observed that the incorporation of dried plants appeared to be more effective that decoctions. Rashidinejad et al. (2016) evaluated the incorporation of green tea extract (GTE) into full-fat cheeses at 250, 500, and 1000 ppm, to determine the effect of green tea catechins on antioxidant properties and microstructure of cheese, and recovery of catechins. Results showed that the incorporation of GTE significantly decreased the pH of whey and curd during cheese manufacture and ripening (P < 0.05), nonetheless there was no significant (P > 0.05) effect on moisture, protein, or fat contents. Microscopy images showed that distribution of milk fat globules entrapped in casein proteins was disrupted by GTE, contrary to the regular and homogeneous structure showed in the ripened control cheese. Ribeiro et al. (2016) evaluated the incorporation of rosemary (Rosmarinus officinalis L.), a woody and aromatic Mediterranean plant, with numerous reported bioactivities (antioxidant, antiinflammatory, antimicrobial antidiabetic, and hepatoprotective). Results showed a decrease of bioactivity for the cheese sample enriched with the free form after 7 days under storage; in contrast the microencapsulated form extracts maintained their antioxidant properties more efficiently through the time of storage thus increasing the bioavailability upon digestion.
Phenolic compounds in dairy products are most employed to improve fermentation because fat content is relatively lower as compared to meat products. Polyphenols also are employed to improve nutritional value of yogurts, being an important source of probiotics, in addition to prebiotics and antioxidants when are added into formulation.
3.3.3. Cereal products
Cereals are the most important food for human in the world. Wheat, maize, rice, and barley are considering the major agricultural cereal grains in the world. Additionally, eight cereal grains: wheat, maize, rice, barley, sorghum, oats, rye, and millet provide 56% of the food energy and 50% of the protein consumed on earth. Recent studies indicate that cereal grains contain significant amounts of phenolic compounds, which are related to reduced risk of chronic diseases. Del Nobile et al. (2009) studied the incorporation of some natural antimicrobial compounds, thymol, lemon extract, and grape fruit seed extract into refrigerated amaranth-based homemade fresh pasta products to enhance their microbial stability. Their results showed that grape extract strongly increases the microbial threshold against the target microorganisms. The most effective antimicrobial compound was thymol, which reduced the growth of psychrotrophic and mesophilic bacteria, and also Staphylococcus spp., having no significant inhibiting effect against total coliforms. On the other hand, lemon extract was the least effective in delaying microbial growth, especially on total psychrotophic and mesophilic bacteria. Neither of these natural compounds showed a significant influence on the sensorial characteristics of the products elaborated with them. Anson et al. (2010) studied the bioaccessible compounds from wheat fractions of aleurone, brand, and flour after their digestion in a dynamic in vitro model of the upper gastrointestinal tract. Results showed that bioaccessible compounds from aleurone had the highest antioxidant capacity and provide a prolonged antiinflammatory effect that those of brand and flour. Sun-Waterhouse et al. (2011) studied the effects of added fruit polyphenols and pectin on the rheological and physicochemical properties of breads; their results showed that breads containing added polyphenols and pectin affected the interactions between water and bread components (such as gluten proteins) during dough development and bread baking, causing differences in bread crosslinking microstructure and textural properties, which ultimately influenced the extractability and/or stability of added polyphenols. Misan et al. (2011) reported that the mixture of ethanolic extracts of some medicinal plants of parsley, buckthorn, mint, caraway, and their mixture called “Vitalplant” can retard the process of lipid oxidation in cookies. Significantly different amounts of total phenolics were reported among extracts, with a greater content in mint and the lowest in caraway. The addition of “Vitalplant” at 2%, 4%, and 6%, improved antioxidant activity and oxidative stability of the cookies in a dose-dependent manner. Yu et al. (2013) investigated the antioxidant properties of refined and whole wheat flour in bread elaborated with each. The data showed that whole wheat flour and bread have superior in vitro antioxidant properties with respect to refined flour and bread elaborated with it.
Polyphenols from agroindustrial coproducts are employed as antimicrobials and antioxidants in cereal foods. Probably the fiber content is adequate, but lacking of pigments made possible the incorporation of these compounds.
3.4. Phenolic Compounds Effects In Vivo
Qingming et al. (2010) evaluated the in vivo antioxidant activity of malt extract from barley in Kunming mice. Scavenging effects on the hydroxyl and superoxide radicals, and protection against ROS-induced lipid, protein, and DNA damage were evaluated. The ability of malt extract to behave as an antioxidant was evaluated by inducing mice with d-galactose. Results in both in vitro and in vivo evidenced its ability to scavenge hydroxyl and superoxide radicals, high-reducing power, and protection against macromolecular (lipid, proteins, and DNA) oxidation damage. They concluded that the malt can be used as an antioxidant for diseases caused by ROS. Price et al. (2012) studied the effects of a diet high in wheat aleurone on plasma antioxidants status, markers of inflammation, and endothelial function. Seventy-nine healthy, older, overweight Northern Ireland people incorporated either aleurone-rich cereal products (27 g aleurone/day), or control products balanced for fiber and macronutrients, into their habitual diets during 4 weeks. The results showed that, compared to the control, consumption of aleurone-rich products provided substantial amounts of micronutrients and phytochemicals, which may function as an antioxidant.
3.5. Methods of Analysis of Phenolic Compounds
The methods available for measuring the total antioxidant capacity depend on the chemical principles of antioxidant capacity assays and the reactions involved in each one. The assays can be classified into two types: (1) assays based on hydrogen atom transfer (HAT) reactions, and (2) assays based on single electron transfer (SET). The majority of the HAT-based assays apply a competitive reaction scheme, in which antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo-compounds (Huang et al., 2005). Characteristics that should be considered in the standardization of an assay include (1) analytical range, (2) recovery, (3) repeatability, (4) reproducibility, and (5) recognition of interfering substances (Pryor et al., 2005).
The SET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes color when reduced, and are the most employed. The degree of color change is correlated with the sample’s antioxidant concentrations. The SET-based assays include the total phenols assay by Folin–Ciocalteu reagent (FCR), Trolox equivalence antioxidant capacity, ferric ion reducing antioxidant power (FRAP), “total antioxidant potential” assay using a Cu (II) complex as an oxidant and DPPH (Huang et al., 2005; Pryor et al., 2005; Somogyi et al., 2007). The FCR is the simplest and is widely used for the evaluation of the antioxidant potential. This method is based on the FCR (simple Folin or phosphomolybdate assay). It is a slightly yellowish golden mixture of hexavalent salts of Mo and W in acidic media that are reduced to blue-color complexes, mainly by the phenolic hydroxyls. The color develops completely after addition of an alkaline salt, such as sodium carbonate. Today, FCR is used to measure the total polyphenolic content in foods and beverages. As a standard reference compound, gallic acid, a compound cheaply available in very pure form, endowed of an average reactivity. Therefore, the total phenolic content is conventionally expressed as Gallic acid equivalent (mg/L GAE). The blue color produced by the FCR with the phenolics is measured by colorimetry at 700–765 nm (Singleton and Rossi, 1965). This test does not entail any special sample preparation other than homogenization of the sample, followed by centrifugation when necessary. Generally, this test gives the first information on the overall phenolic content in a sample, an important data in view of further analyses (Miniati, 2007).
4. Prebiotics
Given the burden and risk of microbial-associated gastroenteritis, the route of using prebiotics to fortify the gut flora and improve colonization resistance holds much potential. Prebiotics have powerful stimulatory effects upon the bifidobacteria that, in turn, exert several antipathogenic mechanisms. Future challenges may include an extrapolation of the prebiotic concept into antiadhesive aspects (Gibson et al., 2005). Consider the following points:
- • Although all prebiotics are fiber, not all fiber is prebiotic. Classification of a food ingredient as a prebiotic requires scientific demonstration that the ingredient: resists gastric acidity, hydrolysis by mammalian enzymes, and absorption in the upper gastrointestinal tract.
- • It is fermented by the intestinal microflora.
- • It selectively stimulates the growth and/or activity of intestinal bacteria, potentially associated with health and well-being (Roberfroid, 2008).
The majority of the scientific data (both experimental and human) on prebiotic effects have been obtained using food ingredients/supplements belonging to two chemical groups: fructooligosaccharides (FOS), the example more important are inulin and the galactooligosaccharides (GOS) (Roberfroid et al., 2010). Another possible candidate as a prebiotic is lactulose.
4.1. Fructooligossacharides
FOS are oligosaccharides that occur naturally in plants, such as onion, chicory, garlic, asparagus, banana, artichoke. They are composed of linear chains of fructose units, linked by β (2-1) bonds. The number of fructose units ranges from 2 to 60 and often terminate in a glucose unit. The length of the chain ranges from 2 to 60 (Sabater-Molina et al., 2009). The most common and studied method to produce FOS is by the transfructosylation of sucrose in a two-stage process (Singh and Singh, 2010). FOS presents important physicochemical and physiological properties beneficial to the health of consumers. For this reason, their use as food ingredients has increased rapidly, presenting a significant growth on the functional food market all over the world (Dominguez et al., 2014).
4.1.1. Inulin
Inulin is a polymer of fructose monomers and is present in such foods as onions, garlic, wheat, artichokes, and bananas and is used to improve taste and mouth feel in certain applications. It is also used as a functional food ingredient due to its nutritional properties. Inulin may be can be used as a replacement for fat or soluble carbohydrates without affecting the taste and texture and still contribute to a foods nutritional value. Enzymatic hydrolyses in the small intestine is minimal (<10%) because inulin consists of beta bonds and is completely metabolized by the microflora; by this, it is considered a prebiotic (Lattimer and Haub, 2010).
4.2. Galactooligosaccharides
GOS are nondigestible, carbohydrate-based food ingredients that can enhance health-related physiological activities (production of SCFAs (Sangwan et al., 2011). GOS molecules are typically synthesized by the enzymatic activity of β-galactosidase on lactose in a reaction known as transgalactosylation (Lomer et al., 2008). GOS provide their health benefits by two main mechanisms: one is by selective proliferation of beneficial bacteria especially bifidobacteria and lactobacilli in the gut, which provide resistance against colonization of pathogens thereby reducing exogenous and endogenous intestinal infections (Sangwan et al., 2011). GOS are mainly used in infant milk formula, and may be able to be incorporated into a wide variety of other foods as: beverages (fruit juices and other acid drinks), meal replacers, fermented milks, flavored milks, and confectionery products (Playne et al., 2009). Commercially available GOS products are mixtures of galactose-based oligosaccharides with varying degrees of polymerization and linkage configuration. GOS are safe and well-tolerated ingredients up to intake levels of 20 g/day; they have GRAS status in the United States, FOSHU status in Japan, and can be included in the DF content of foods (Torres et al., 2010).
4.3. Lactulose
Lactulose is caused by the isomerization of lactose to generate the disaccharide galactosyl-β-1,4-fructose (Venema and Do Carmo, 2015), which is present in milk and dairy products, causing acidification of the intestinal environment and a decrease in pH, and is a substrate for bifidobacteria and lactobacilli (Caselato de Sousa et al., 2011). In the large intestine, lactulose is metabolized by some species of the colonic microflora, which exhibit a matching galactosidase activity. This selective metabolism of lactulose alters the microbial balance and the biochemical composition of cecal contents (Schuster-Wolff-Bühring et al., 2010).
Lactulose is applied in a wide variety of foods as a bifidus factor or as a functional ingredient for intestinal regulation. In addition to providing useful modifications to food flavor and physicochemical characteristics, many of these sugars possess properties that are beneficial to the health of consumers. Additionally, lactulose can be used as a sweetener for diabetics, too. It also has some properties with desirable effects in food products, such as flavor-enhancing properties, favorable browning behavior, and excellent solubility in water (Panesar and Kumari, 2011).
4.4. Prebiotic Activity In Vitro
Sendra et al. (2008) studied the incorporation of Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum with lemon and orange fibers. Citrus fibers enhanced bacterial growth and survival of the tested probiotic bacteria. This study indicated that citrus fibers have good acceptability and are good vehicles for a variety of commercial probiotics. Díaz-Vela et al. (2013) evaluated the cactus pear and pineapple peel flours as an alternative carbon source during fermentation from lactic acid bacteria with probiotic potential, cactus pear peel, and pineapple peel flours produced acceptable results as a carbon source, obtaining satisfactory prebiotic properties. In conclusion, cactus pear and pineapple peel flours can be used as functional ingredient due to their fermentable properties in addition to their high total DF and antioxidant properties. The prebiotic activity of grapefruit albedo was evaluated with two lactic acid bacteria strains; the results showed a specific growth rate was higher and with a lower duplication time, SCFA production confirms the prebiotic potential of this coproduct (Parra-Matadamas et al., 2015). Ozcan and Kurtuldu (2014) studied the effects of using DF barley and oat β-glucan as a prebiotic on the viability of B. bifidum in probiotic yogurt and properties of yogurt during storage were investigated. The survival of B. bifidum was within biotherapeutic level (>7 log cfu/g) as a result of the prebiotic effect of barley- and oat-based β-glucan. The addition of β-glucan to yogurt significantly affected physicochemical properties including pH, titratable acidity (LA%), whey separation, color (L*, a*, b*), and sensorial properties of yogurts. β-glucan can be used on the development of cereal-based functional dairy products with sufficient viability and acceptable sensory characteristics.
5. Future Perspectives for Coproducts Agroindustrials
Agroindustrial coproducts are a rich source of nutrients, like fiber and polyphenols. Their processing to convert this food industry disposal into added-value functional food ingredients is now being studied and is a promissory line of investigation and business opportunity. Countries with the adequate wheat allow fruits cultivation and can use the overproduction of noncommercial, some fruits in addition to employ the peels derived from juice processing. These processed coproducts are the source of fiber and antioxidants.
Encapsulation with agroindustrial coproducts is another novel application to improve food functionality. On the one hand, it serves as protection for probiotics during and after food manufacturing, shelf life, and consumption. On the other hand, both prebiotic and probiotic can be incorporated as a functional ingredient.
6. Conclusions
Agroindustrial coproducts are a cheap and available source of functional ingredients like fiber, antioxidants, and prebiotics. The use of these coproducts as food ingredients decrease the environmental impact if these are not correctly disposed, because they are organic matter. In same manner, fruit peels are cheaper underemployed resources than cereal coproducts. Their applications can cover almost all processed food products, especially animal origin foods.