Bioactive substances and product development of cereals www.immy.cn
Bioactive substances and product development of cereals www.immy.cn
Whole grains are rich in dietary fiber, vitamins, minerals and other nutrients, and contain phenolic acids, tannins, anthocyanins and phytosterols and other bioactive substances. In view of these nutritional characteristics, there is great potential for basic research and further development of cereals. In order to provide new ideas for the processing and further research of coarse grain crops, the bioactive substances of coarse grains and the nutritional components, product development and health care functions of five representative coarse grain crops were reviewed, and the research conclusions and development suggestions of coarse grains were obtained.
Coarse grains refer to cereals other than wheat, rice, or cereals that are mainly used for animal feed and winemaking. These cereals are mainly produced in the semi-arid tropics of Asia and Africa, where rain-fed farming methods result in low grain yields per unit area (typically less than 1 t/hm2) [1]. Coarse grains mainly include corn, sorghum, oats, barley, millet, barley and amaranth. They are rich in phytochemicals with antioxidant properties, such as dietary fiber, vitamins, minerals (especially micronutrients such as iron and zinc) [2]. In view of these nutritional properties, cereals are labelled as nutritious foods. Several epidemiological studies have shown that these cereals help fight a variety of chronic diseases such as ischemic stroke, cardiovascular disease, cancer, obesity, and type II diabetes [3-4]. Multigrains have a rough taste and cannot replace our staple grains, but they can be combined with rice and wheat in different proportions to make a variety of nutritious products. Due to their high protein content and balanced amino acid composition (methionine, cystine, and lysine), they are nutritionally comparable to, or even better than, major cereals such as wheat and rice [5]. In recent years, with people's increasing attention to food nutrition and safety, the demand for "diversified, nutritious, healthy, safe and convenient" miscellaneous grains in the international and domestic markets has been increasing, which has made all kinds of miscellaneous grains have good development prospects and can penetrate into the diets of consumers, including consumers in rural and urban, developed and developing countries. The research and development of the potential uses of these cereals have shown the potential of cereals as formula foods. In addition to being used as food, these grains are also used as feed, syrups, winemaking, biofuels, or biopolymers [6].
1 Bioactive substances in coarse grains
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1, The various components of multigrains are biologically active in addition to providing nutrients.
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Among the phenolic compounds include phenolic acids, tannins, coumarins, flavonoids, and alkylresorcinol. Phenols play an important role in the flavor, texture, color, and oxidative stability of plant-based foods [7]. They have special nutritional properties and are usually found in the bran. There are two types of phenolic acids: hydroxycinnamic acid and hydroxybenzoic acid. Hydroxybenzoic acid includes parahydroxybenzoic acid, vanillin, syringic acid, and protocatechuic acid, while hydroxycinnamic acid includes coumaric acid, caffeic acid, ferulic acid, and sapic acid.
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Cereals contain a high concentration of tannins, whose main function is to protect the grains from mold contamination to prevent the grains from spoiling, and at the same time, the tannins are also one of the reasons for the bitter taste of the grains. Tannins reduce the digestibility of proteins, carbohydrates and minerals and have gastrointestinal protection, anti-cancer, anti-ulcer and cholesterol-lowering properties. Turngrass is the only millet that contains tannins. Avenanthramides are amides of cinnamoylanthranilic acid and are found only in oats. It has anti-inflammatory, anti-atherosclerosis, and antioxidant properties[8]. Alkylresorcinols produced by various plants, bacteria, and fungi are bioactive compounds that benefit human health, such as anticancer activity [9-10].
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Flavonoids include anthocyanins, flavanols, flavanones, and flavonoid bases. Grains contain a variety of flavonoids, which are usually found in the peel. The 6 common anthocyanins found in cereals are cornflower pigment, mallow pigment, pelargondin, delphinium pigment, petunia pigment, and peony pigment. 3-Deoxyanthocyanins are a unique member of the anthocyanin group that is stable at high pH, which is what makes sorghum a good natural food colorant [11]. The flavonoids in millet are mazein, isomazein, vitexin, isovitexin, saponin and valervin, while vitexin glucoside, glucovite, and vitexin are vitexin glucoside, glucovite, and vitexin in pearl millet. Oats are apigenin, glycosyl vitexin, isovitexin, wheatlavinin and vitexin.
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Lignans are a class of phytoestrogens found in barley, oats, rye, and rye. The lignan content in these grains ranged from 8 to 299 μg/100 g [12]. Plant sterols are cholesterol compounds that are mainly found in bran. Most of the phytosterols in grains are in free form, and a few such as fatty acid esters or hydroxycinnamic acid (usually ferulic acid) can be combined with sugars (mainly glucose) to form glycosides. Each 100 g of sorghum contains 46~51 mg of unbound phytosterols [13], and corn, barley and oats contain 70~88 mg/100 g, 55~76 mg/100 g and 35~46 mg/100 g [10], respectively.
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Dietary fiber is the edible part of the plant and is not hydrolyzed by enzymes in the digestive tract. Oligosaccharides such as lactulose, fructooligosaccharides, and trans-galacto-oligosaccharides have been reported to be effective in promoting the growth of bifidobacteria and lactobacilli in the human large intestine. Several oligosaccharides found in cereals are galactose derivatives of sucrose, stachyose, and raffinose, as well as fructose-based derivatives of sucrose and fructooligosaccharides [12]. Cereals do not contain vitamin C, vitamin B12, vitamin A, and β-carotene [14]. However, they are a great source of most B vitamins, especially thiamine, riboflavin, and niacin [15]. Cereals also contain a certain amount of vitamin E.
?Whole grains contain a variety of anti-nutritional factors that limit their nutrient content, mainly phytic acid and polyphenols [16-17]. It has been reported that phytic acid content is significantly reduced during germination due to phytase activity. The reduction was greatest in the first two days of germination and smaller on days 4 to 6 of germination [18]. Phytase activity can be observed during germination in barley, rye, and oats, which hydrolyze phytic acid into phosphate and inositol phosphate. Similarly, a decreasing trend in polyphenol content was observed between germination and day 6 of these grains [19]. The increase in the protein content of sprouted cereals may be due to a decrease in the number of antinutritional factors (tannins, polyphenols and phytic acid), as well as other macromolecular substances, especially carbohydrates. Blanching significantly reduced polyphenol content (28%) and phytic acid content (38%)
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2?R&D of cereal products
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2.1 Barley products
Barley is a versatile grain. In food, barley grains are ground to produce barley flour grains, which can be further processed into coarse grains, flakes, and flours. It resembles wheat fruit in appearance, but is slightly lighter in color. Malted barley is rich in maltose, which can be made into maltose syrup, which is commonly used as a sweetener in food. Barley is fermented and used as an ingredient in beer and other alcoholic beverages. In Western countries, whole, flaky or ground barley flour grains are used in breakfast cereals, stews, soups, porridges, breadcrumbs, and baby food [20]. Barley flour can also be added to wheat products such as: bread, cakes, biscuits, noodles, and squeezed snacks.
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Wheat bread made with 15%~20% barley flour is acceptable, but an increase in the proportion of barley flour will cause the bread to shrink in size, harden in texture, and dark brown in color [21]. Wheat noodles made with 12%~25% barley flour have acceptable noodle-making characteristics [22]. Barley tea is widely drunk in Asia, and it is made from roasted barley kernels [23]. The second largest use of barley is malt, which is used in the production of beer, distilled alcohol, malt syrup, malted milk, condiments, and breakfast foods, among others.
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With the rapid development of the world's nutritional and health food production, the development and utilization of barley food has attracted the attention of food experts at home and abroad, and is considered to be a hot spot for the development of new foods in a certain period of time in the future.
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2.2 Oat products
Oats are eaten in a variety of forms and can be made into a variety of edible products. Internationally, oatmeal is the most common oat food, in China's oat producing areas, oats are often processed into oat flour, also known as noodles, and then make a variety of oat pasta. Oats are eaten as is, mainly used as porridge and can also be used to mix and make a variety of baked goods such as oatcakes, oatmeal cookies, and oatmeal bread. Oats are rich in dietary fiber, both soluble and insoluble. It's also rich in essential fatty acids like linoleic acid and oleic acid, which help lower LDL cholesterol and HDL cholesterol, and it's also rich in minerals like magnesium, potassium, and calcium, making it a good source of folate, which is needed for cardiovascular health. Oat alkaloids are antioxidants unique to oats, which inhibit the formation of oxygen free radicals. Due to its high fat content, oat flour is sticky and not easily sifted, replacing it with the more common whole-grain oat products – oat rice and oatmeal. The polar lipid moiety of oat oil is suitable for use as an emulsifier [24]. Oat flour is used as an ingredient in a variety of bread and bakery products because of their unique flavor and moisturizing properties in addition to enhancing the nutritional value of these products. In the traditional wheat bread recipe, the addition amount of oats is as high as 10%~20%. By optimizing the baking technique, it is even possible to add more oat flour [25]. Using oats as a matrix, lactic acid bacteria and probiotic drinks can be prepared. The starter culture, oat flour and sucrose content affect the fermentation process. During fermentation and storage, the β-glucan content in the beverage remains the same. This beverage can be stored under refrigerated conditions for 21 days [26].
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?A novel low-fat mayonnaise can be prepared from oat dextrin with a glucose equivalent of 8.1, a viscosity of 1620 MPa-s, and a calorific value of 597.7 kcal/100 g [27].
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2.3 Sorghum products
Sorghum has a higher insoluble fiber content, which leads to a lower rate of hydrolysis of sugar, so sorghum food is more suitable for diabetics. For example, sorghum products have been shown to lower blood sugar levels in diabetics compared to wheat preparations. Biscuits made from sorghum flour are suitable for diabetics, and the raw materials of the biscuits are a mixture of 40% wheat flour and 60% sorghum flour, which is high in fiber. It is well known that the moist heat treatment of sorghum reduces its digestibility. During processing, starch retrogradation occurs, resulting in the formation of resistant starch and an increase in dietary fiber content [28]. Therefore, tannic sorghum has potential applications in diabetic foods. Tannin sorghum is characterized by slow digestion. Africa's food culture is more skewed towards tannin sorghum because it provides a longer feeling of fullness compared to other grains. Sorghum is gluten-free, and it is also a potential source of nutrients, such as antioxidant phenols and cholesterol-lowering waxes [29].
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2.4 Millet products
Millet is an important small grain crop that is mainly cultivated in mainland India and Africa and is one of the oldest cultivated crops in the world. Millet is the main product of millet milled and processed, and it is a traditional grain product that people in China especially like to eat. In recent years, it has become increasingly important due to its nutritional properties. In addition to being a staple food, millet can also be used to make snack foods such as noodles, gummies, and vitamin C. Millet products have a high mineral content, but antinutrients such as phytic acid and polyphenols affect the in vitro digestibility of protein and starch. Acid-treated millet products are more acceptable than peeled millet products. Millet is mixed with soybeans or other protein-rich products, such as beans or peanuts, to create a nutritionally balanced complementary food. Studies have shown that the protein content of extruded millet products mixed with 30% cereal soybean meal or 15% defatted soybean meal is 14.7% and 16.0%, respectively [30]. Noodle products such as noodles, macaroni, etc., can be made from millet flour. Squeezed snacks made with rice flour, corn flour, or tapioca and millet flour in different proportions are acceptable in appearance, color, and texture. Millet is rich in oil and linoleic acid, accounting for 4% of the total fatty acids of oil, and its proportion of n-3 fatty acids is higher than that of corn, while linoleic acid in corn accounts for only 0.9% of the total fatty acids. N-3 fatty acids play an important role in physiological functions such as platelet aggregation, LDL cholesterol accumulation, and the immune system [31]. Millet bran contains a high proportion of soluble dietary fiber, which has cholesterol-lowering and hypoglycemic effects.
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2.5 Corn products
In addition to being used as human food and animal feed, corn is an important source of a large number of industrial products. Food additives include corn fiber oil, corn cellulose gum, cellulose fiber gel, xylo-oligosaccharides, and ferulic acid, vanillin, and xylitol are also useful by-products. Corn gum can be used as a binder, thickener, or additive in plastics, and corn starch can be used to produce corn syrup, maltodextrin, glucose, and starch [32]. Refined corn oil is 99% triacylglycerin, which includes 59% polyunsaturated fatty acids (PUFAs), 24% monounsaturated fatty acids (MUFAs) and 13% saturated fatty acids (SFAs). Mendonca et al. [33] found that adding corn bran to extruded snacks at a ratio of 150~320 g/kg could significantly reduce the radial expansion rate, appearance, and general acceptability of the finished product. Holguin Acuna et al. [34] found that corn bran with 300 g/kg and 400 g/kg had the lowest breaking strength, and extrusion could improve the poor properties of corn bran in baked goods. The cellulose fiber gel prepared from corn bran can be used as a fat mimetic for popularization. Corn bran and fiber can also be used as a substrate for the production of xylitol, a low-calorie, non-carcinogenic sweetener.
?3, The use of cereals in other industries
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The potential properties of sorghum granular polymers in the preparation of biodegradable, edible bioplastic films and coatings are being studied. Sorghum gliadin is one of the options for the preparation of bioplastics because it is the most hydrophobic of gliadin [35]. Single grains or a combination of two or more grains have been used to produce a variety of beers. Sweet sorghum can be used to make sugar, alcohol, syrup, sesame paste, feed, fuel, bedding, fencing, and papermaking.
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The development of coarse grains should focus on their potentially useful properties with a view to producing unique alternative value-added products. With the promising potential and health benefits of the food processing industry, the commercialization of multigrain foods needs to be viewed from a broader perspective, from production to utilization, as well as the challenges and opportunities that will be faced in the future.
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4.Conclusions and recommendations for development
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At this stage, the products developed by coarse grains in China still have defects such as rough taste, unattractive appearance, and unbright color, which is an important factor restricting the consumption of coarse grain products. At the same time, coarse grains are rich in bioactive substances, and making full use of coarse grain resources to develop various functional foods and health products is an important direction for the development of coarse grains. Therefore, it is necessary to comprehensively consider the processing characteristics, nutritional characteristics and consumer preferences of food to conduct research, so that the products can not only retain the unique flavor characteristics of cereals, but also meet people's taste requirements [36]. According to the characteristics of different cereals and people's consumption habits, the deep processing of coarse grains raw materials into convenience foods, snack foods, and food ingredients, such as extruded and cooked instant noodles, single or compound coarse grain puffed powder, and cereal-based probiotic foods [37].
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In terms of economic benefits, coarse grains have great potential for processing and development, and the value-added of processing is large. For example, millet can be added by 1~3 times when processed into high-quality rice, and millet can be added by more than 5 times when processed into primary products such as millet crisp. Deep-processed fine products will add more value and profits will be higher. International experience shows that compared with raw grains, the value-added range of intensively processed coarse grain products has reached several times to dozens of times, and the value-added potential is huge. With the development of consumption and the scientific and technological progress of the processing industry, functional foods have become an important direction for the development of the global food industry, and functional foods have attracted the most attention for their health care functions and involved the largest variety of products. Most of the grains themselves have health care functions, and if they are combined with some nutrients, active substances, new resource foods, etc., they may be combined into a variety of products.
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At present, the development of cereals is generally in the initial stage, and the research and development and application of advanced food processing technology need to be strengthened. Improving the sensory level of miscellaneous grains and developing a variety of products are important tasks to be solved. In summary, it is necessary to further strengthen the basic and applied development research of cereals, strengthen the research on the development and comprehensive utilization of new cereal health foods, and the processing research of compound cereal products, so as to develop cereal products that meet the market demand and consumers' preferences.
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