Functional Foods from Cereal Grains

Abstract

Cereal grains and germs are good sources of various phytochemicals. The major phytochemicals present in cereal grains are: phenolic acids, flavones, phytic acid, flavanoids, coumarins, and terpenes. Cereal germs are good sources of ferulic acid, phytic acid, glutathione, and phytosterols. In addition, the cereal germ acontains the vitamins E, B₁, B₂, and B₃, the minerals P, K, Mg, Ca, Zn, and S, and fiber. Because of its rich nutrient content, cereal germ would be a valuable ingredient for production of functional foods. Our article examines the feasibility of using constituents of selected cereal grains such as wheat, oat, psyllium, and barley in producing functional foods.

Keywords:

• Cereals
• Baked products
• Grains
• Functional foods
• Germ
• Chemical composition
• Psyllium
• Oats
• Barley
• Phytochemicals

INTRODUCTION

The most recent research shows that the consumers are becoming more aware of the relationship between diet and disease,[1–2] and there is a gradual shift from animal-derived to plant-based meals.[3] A number of phytochemicals present in plant foods have been shown to have a positive effect on health and disease prevention.[4] Free radical-mediated lipid peroxidation has been implicated in a variety of pathological processes, especially in both the initiation and promotion of atherosclerosis and diabetes.[5] Vitamin E, phenolic compounds, glutathione, ascorbic acid, beta-carotenes, selenium, and copper are the major antioxidants that are known to prevent oxidation process.[6–9] Among the major cereals, wheat is the staple food in the diets of a large segment of the world's population. It accounts for nearly 20 to 80% of the total food consumption in various regions of the world. Apart from being rich in a number of phytochemicals, wheat has unique gluten forming properties, which makes it suitable for the production of a large number of baked products. Oats, psyllium, and barley hold a significant place in human diet in various regions, and they are also rich in phytochemicals.[10]

The recent survey in the United States shows that more and more people believe that foods can be designed to help prevent disease.[11] The concept that phytochemicals can play a role in the prevention of cancer can be extended to other chronic diseases like arthritis, coronary heart disease and osteoporosis among others.[12] The major phytochemicals present in cereal grains are: phenolic acids, flavones, phytic acid, flavanoids, coumarins, and terpenes. Cereal germs are good sources of some of these phytochemicals i.e., ferulic acid, phytic acid, glutathione, and phytosterols. The cereal germ also contains vitamins (Vitamin E, B₁, B₂, and B₃), minerals (P, K, Mg, Ca, Zn, and S), and fiber. Because of its rich nutrient content cereal germ would be valuable ingredient for production of functional foods.[13] Recent implications of a role in disease prevention and treatment, together with the increasing health care costs have increased interest in functional foods not only among the food scientists, but also the consumers, regulatory agencies, food producers, and processors. This article examines the feasibility of using constituents of select cereal grains such as wheat, oat, psyllium, and barley in producing functional foods.

STRUCTURE OF CEREAL GRAINS

Like other cereals, wheat (Triticum aestivum L.) grain consists of 3 main anatomical parts: an embryo (germ), an endosperm, and a pericarp (bran). The germ, endosperm and bran constitute 3, 82, and 12% of the whole wheat kernel, respectively.[14] Wheat grain measures approximately 8 mm in length and weighs about 35 mg, but the size of kernel varies depending on the cultivar and their location on the head or spike. The wheat kernel has a longitudinal crease that runs the entire length of kernel on the ventral side. This crease not only makes it hard for the miller to separate the bran from the endosperm but harbors microorganisms and dust. The seed coat contains a pigment strand that determines the color of wheat kernel. It is usually white or red and is determined by genetics. With genetic manipulation, the plant breeder can select desired color for the wheat kernel.

Wheat kernel has one cell thick aleurone layer, which completely surrounds the starchy endosperm and the germ. During milling, bran and germ are separated from the endosperm. Most of the endosperm fraction ends up in white flour (71%), and the part of endosperm (like aleurone layer) which can not be separated from bran and germ, ends up as shorts.

Barley (Hordeum vulgare L.) and oat (Avena sativa L.) grains are different from wheat, as these are harvested with hull intact. Average barley kernel weighs about 35 mg. Under the hull, the barley and oat caryopsis, just like wheat, are composed of pericarp (bran), germ, and endosperm. Some of the barley and oat cultivars are hull-less just like wheat kernels and are known as naked or hull-less types. These cultivars find extensive uses in functional food product development, because the hulls are highly lignified and fibrous, and are not suitable for human consumption. The caryopsis of oat is known as groat and is similar in appearance to the wheat kernel, except that it has several hair like structures on one of its ends. The oat germ is narrower but slightly larger than the germ of wheat.

Psyllium (husk material of Plantago ovata) is a very good source of soluble dietary fiber, containing about 85 g soluble fiber/100 g and the psyllium husk possesses considerable gelling and water-absorbing capacity.[15] Psyllium husk binds a lot of water (2–3 g water/g polymer) to form a solid and stiffer gel, the greater part of water in the gel is free and behaves like liquid water.[16] The gel-forming component of psyllium seed husk (PSH) is not fermented and is responsible for the laxative and cholesterol-lowering properties of this fiber. This gel-forming fraction B is about 55% of the PSH and is poorly fermented; it is also a component that increases stool moisture and fecal bile acid excretion, thus leading to lower blood cholesterol levels.[17] Fraction C, representing < 15% of PSH, is viscous, but is rapidly fermented in the colon. Fraction A is an alkali-soluble material that is not fermented by typical colonic microflora. Fractions A and C do not alter moisture and bile acid output. The active fraction of PSH is a highly-branched arabinoxylan consisting of a xylose backbone and arabinose- and xylose-containing side chains.

Ahluwalia, Sidhu, and Kaur[18] have studied the effect of psyllium addition on the rheological properties of wheat flour. With the addition of psyllium, they observed higher water absorption and stability but decreased mixing tolerance. Amylograph peak viscosity increased with the addition of psyllium to flour. Czuchajowska, Paszczynska, and Pomeranz[19] have added psyllium to wheat flour at 2, 4, and 8% for producing Chinese steamed bread, Japanese noodles, cakes, and regular white pan bread. Psyllium impaired volume and quality of steamed bread, discolored noodles, but it did not affect their taste and texture, and it increased the loaf volume of bread. The higher water content of the pan bread crumb containing psyllium was not accompanied by an increase in water activity and showed improved softness retention after 72 hours of storage.

COMPOSITION OF CEREAL GRAINS

The chemical composition of cereal grains and their anatomical parts varies with the cultivars, agronomic conditions and soil fertility level, but a generalized composition can be considered for most practical purposes. Table 1 shows the ash, protein, fat, and carbohydrate contents of wheat grain and its anatomical parts.[20] As shown, germ is high in protein and vitamin E (tocopherols and tocotrienols) with values reaching up to 500 ppm.

Table 1 Proximal composition∗ of various wheat grain anatomical parts and wheat flour

Grain or its part	Ash, %	Protein, % (N × 5.7)	Fat, %	Crude fiber, %
Straight grade flour (WF)	0.64 ± 0.02	11.01 ± 0.15	1.04 ± 0.10	0.16 ± 0.01
Whole wheat flour (WWF)	1.25 ± 0.01	13.40 ± 0.01	1.70 ± 0.06	1.50 ± 0.06
Coarse bran (CB)	5.18 ± 0.01	13.29 ± 0.03	2.73 ± 0.02	10.09 ± 0.06
Fine bran (FB)	4.55 ± 0.08	16.29 ± 0.13	3.55 ± 0.18	5.96 ± 0.11
Psyllium husk (PS)	2.58 ± 0.03	2.53 ± 0.06∗∗	0.73 ± 0.15	2.63 ± 0.08
Wheat germ (WG)	3.78 ± 0.05	24.24 ± 0.07	7.99 ± 0.11	2.53 ± 0.04
∗Average and Standard Deviation of three replications (14% Moisture Basis); ∗∗N × 6.25 factor was used for psyllium. (Source: Sidhu et al.[20]).

PHYTOCHEMICALS IN CEREAL GRAINS

The food industry is geared towards producing functional foods based on various cereals due to consumer demands for healthier foods. Cereals such as wheat, barley, psyllium and oats being rich in many phytochemicals and other nutrients, offer an excellent opportunity for the production of functional foods. The many beneficial properties of these cereals can be utilized in ways leading to the design of novel cereal-based functional foods that can target special needs of populations.[21]

DIETARY FIBER

Dietary fiber is one of the major phytochemicals present in cereals, which can be divided into two categories according to their water solubility. Water-soluble fraction (soluble fiber) consists mainly of nonstarchy polysaccharides such as beta-glucans and pentosans (arabinoxylan). Soluble fiber is known to decrease serum cholesterol, postprandial blood glucose, and insulin levels in humans.[22] Water-insoluble fraction (insoluble fiber) consists of lignin, cellulose, hemicellulose (water-insoluble arabinoxylan). The dietary fiber contents of cereals vary depending on cultivars, their botanical components (such as pericarp, endosperm, and germ) and the processing conditions they have undergone.[23] The average values for the total dietary fiber in barley, wheat and oats have been reported to be 10, 12, and 14% (dry basis), respectively.[21]

Beta-glucans in cereals are other important sources of the dietary fiber. These are unbranched polysaccharides consisting of (1→ 4) and (1→ 3) linked β-D-glucopyranosyl units in varying proportions. Beta-glucans have been reported to have important positive therapeutic effect on coronary heart disease (CHD) thru the reduction of cholesterol and glycemic control.[24] Beta-glucans from oats and barley have been shown to lower serum cholesterol levels in hypercholesterolemic subjects, thus lowering the risk of CHD. Among the cereals, barley and oats are the richest sources of beta-glucan, ranging from 3–11% and 3–7% on dry basis (db). These beta-glucans are usually concentrated in the aleurone and endosperm cell walls of barley,[25] oats,[26] and wheat.[24] Hydrolysates of oat beta-glucans have been reported to stimulate the growth of some probiotic bacteria such as Bifidobacterium strains and L. rhamosus.[27]

Cereals are good sources of 2 types of oligosaccharides, which have been shown to stimulate the growth of bifidobacteria and lactobacilli in human large intestine. Henry and Saini[28] have characterized these as galactosyl derivatives of sucrose, stachyose and raffinose, and fructosyl derivatives of sucrose, fructo-oligosaccharides. Wheat and barley grains show variations in some of the carbohydrate and essential amino acid contents during development. Meals from immature kernels are reported to contain high lysine, fructans, and simple sugars and therefore, could be used in functional foods.[29] Wheat germ and bran fractions are especially rich in these oligosaccharides having 7.2% and 11.1% (db) compared with that of 1.2–1.6% in flour, respectively.[14,30] Resistant starch (not digested by salivary amylases) has been shown to provide benefits for the production of desirable metabolites such as short-chain fatty acids (SCFA) in the large intestine. Prebiotics can be developed from this resistant starch in the large intestine for decreasing the risk of bowel diseases.[31]

One of the most promising areas of product development is the use of resistant starch from cereals as a substrate for probiotics. Lactic acid fermentation of wheat and rye flour for the production of sour-dough bread is a traditional method. The starter cultures are characterized as “mixed-strain cultures,” which are continuously propagated and maintained by the bakeries. Starch, water-soluble and water–insoluble pentosans, beta-glucans, and several free sugars, such as sucrose, maltose, fructose, glucose, stachyose, xylose and arabinose, are the major carbohydrate constituents of the cereal grains, and their content varies depending on cultivars.[32] The higher amounts of free sugars and amino acids present in the growth medium (especially due to the use of cereal malts) supports better cell growth for Lactobacillus plantarum and other lactic acid bacteria.[33] Compared with L. acidophilus, L. plantarum grows well even under low pH conditions of the sour-dough as it has a unique ability to tolerate higher amounts of lactate.

OTHER PHYTOCHEMICAL CONSTITUENTS OF CEREALS

Due to their slow fermentability and higher water-holding capacity, some other wheat bran components, such as lignin, and cellulose, are shown to be protective against colon cancer. Wheat bran also has the ability to bind to cytotoxic substances such as bile acids and other mutagens, lowering their bioavailability in the colon.[34–35] Induction of cytochrome P-450 dependent enzymes in the small intestine by wheat bran intake may also be involved in this protective action. Non-fiber components of wheat bran including phytic acid and phenolic compounds are also shown to provide anti-carcinogenic effects.[22] Phytic acid, a natural plant antioxidant present in wheat bran in relatively high amounts (4.8%), has the ability to suppress iron-catalyzed oxidative reactions. Phytic acid is known for its inhibitory effects on trace mineral bioavailability, but has recently received attention as anti-cancer compound.[10,36–37] The mineral chelating ability of phytic acid may be responsible for its inhibitory effect on oxidative reactions.

PHENOLICS

The bran layers of cereal grains are relatively rich in antioxidants. These antioxidants are either water- or fat-soluble and nearly one half are insoluble. Soluble antioxidants in oats include phenolic acids, flavonoids, tocopherols, tocotrienols, and avenanthramides.[10] A major portion of these insoluble antioxidants are cinnamic acid esters bound to pentosans. Insoluble fiber in wheat bran contains nearly 0.5 to 1% phenolics. Though some of the phenolic compounds present in wheat bran have been studied for their potential role in preventing hormone-related cancers, most phenolic compounds (e.g., ferulic acid) are abundant in whole grains, especially in bran layers (764 mg/100 g). These phenolics, which exert synergistic antioxidant action with other bioactive compounds, are mainly present in the outer layers of bran. The combination of some phenolic acids has also been reported to have anticarcinogenic and antibacterial properties.[38] Major phenolic antioxidants in wheat bran are: ferulic, vanillic, p‐coumaric, caffeic, protocatechuic, p-hydroxybenzoic, gentisic, chlorogenic, and syringic acids. Other phytochemicals present in cereals are phytosterines, saponins, and phytoestrogens.[39]

Ferulic acid may provide health benefits because of its antioxidant properties.[40] In addition, ferulic acid present in wheat bran, has been shown to have nitrite scavenging effect as efficient as that of ascorbic acid under acidic conditions.[41] Phytochemicals in grains are usually underestimated since bound phytochemicals are excluded in the total. Major portion of phenolics are found in bound form (75% in oats and wheat). Ferulic acid in grains is present as free, soluble-conjugated and bound in the ratio of 0.1:1:100.[42] Because the bound phytochemicals may survive the digestion process and reach the colon, they may possess anti-cancer properties. This may partly explain the role of whole grain consumption in the prevention of colon cancer. When bound phenolics reach the colon, they are acted on by the microbial enzymes to set them free. Colonic endothelial cells may absorb the free phenolics and gain antioxidant protection when these phenolics enter the portal circulation.[43]

The barley bran polyphenols such as proanthocyanidins (procyanidins and prodelphinidins) have been shown to exhibit similar or higher antioxidative activities than catechins.[44] During barley bran fermentation (lactic acid), a novel purple pigment called hordeumin, a type of anthocyanin-tannin pigment, can be produced. The free radical scavenging activity of this polyphenolic compound increases with the length of fermentation.[45] It is suggested that the free radical scavenging activity of hordeumin results from barley bran polyphenols such as proanthocyanidins.

PHYTOESTROGENS, ANTIOXIDANTS, AND ANTINUTRIENTS

Wheat, barley, and oats are also known to contain many other bioactive compounds such as lignans, phytosterols, isoflavones, resorcyclic acid lactones, coumestans, unsaturated fatty acids, lutein, cryptoxanthin, zeaxanthin, tocopherols, tocotrienols, glutathione, and melatonin. These compounds may affect gastrointestinal physiology and provide protection against chronic diseases like coronary heart disease and some cancers.[46–49] Grains contain more tocotrienols than other food products. The tocotrienols possess vitamin E activity and also inhibit cholesterol synthesis. Vitamin E is a fat-soluble antioxidant present in germ portion of cereal grains, which protects cell membrane from oxidative damage. It also keeps the selenium ions in a reduced state and inhibits the formation of nitrosamines, especially at low pH.[50] The total antioxidant activity of grains has been reported to be higher in wheat (76.7 ± 1.38 μmol vitamin C equiv./g grain) than oats (74.67 ± 1.49 μmol vitamin C equiv./g grain).[42] According to Adom and Liu,[42] bound phytochemicals were the main contributors to total antioxidant activity in wheat (90%), rather than the oats (58%). Bound phytochemicals survive the stomach and intestinal digestive process and reach the large intestine where they may play a protective role against oxidation.

Phenolics and phytic acid are other known antioxidants present in bran layers of cereal grains. Phytic acid forms chelation complexes with various divalent minerals (e.g., iron), suppressing the iron-mediated free-radical oxidant damage created by the colonic bacteria.[10] Depending on the soil fertility level, selenium—another antioxidant—is also available in significant amounts in cereal grains.[51] Selenium is a cofactor for glutathione peroxidase, an enzyme providing protection against oxidative cell damage.

Following the intake of lignans and isoflavones, these compounds are modified by the gut bacteria converting them to biologically active metabolites that are absorbed and subsequently excreted in feces and urine.[52] Although, lignans and isoflavones contents in cereals are low, because of the high consumption of cereals, their contribution to the daily diet is high.[53–55] Lignans are converted to enterolactone in the large intestine, which are absorbed into the blood. The serum enterolactone is positively associated with the lignan intake and has been used as a biomarker for lignan intake.[56] Recent research has shown an association between higher serum enterolactone with reduced Cardio Vascular Disease (CVD)-related and all-cause mortality in Finnish men.[57] In addition to naturally present antioxidants, antioxidant activity is also generated by non-enzymatic browning reactions during the baking and toasting processes. The total antioxidant activity of whole grain baked products is reported to be similar to that of fruits or vegetables.[58]

Grains also contain certain antinutrients such as digestive enzyme (protease and amylase) inhibitors, phytates, haemagglutinins, phenolics, and tannins. These compounds have been shown to have some beneficial effects, also. Protease inhibitors, phytates, phenolics, and saponins have been reported to reduce the risk of colon and breast cancer in animals. Phytates, lectins, phenolics, amylase inhibitors, and saponins may lower plasma glucose, insulin, and /or improve the blood lipid profile in humans.[50] Alkylresorcinols (AR), present in whole grain cereals, are important biomarkers to link the consumption of whole grain cereals and their observed health effects. About 60% of the AR is absorbed from the small intestine by humans. The extent of absorption and their presence in serum can be used as a biomarker of whole grain cereal intake.[59]

PHYTOSTEROLS AND UNSATURATED FATTY ACIDS

Some plant sterols and stanols present in oilseeds, grains, nuts, and legumes are reported to reduce the serum cholesterol.[60] Except side-chain methyl and ethyl groups, these plant sterols are structurally quite similar to cholesterol. As plant sterols have better solubility than cholesterol, they inhibit the biliary cholesterol absorption from the small intestine. It is not clear how much plant sterols must be consumed to have an optimal benefit, but a daily intake of 1–2 g is usually recommended.[61] The average Western diet supplies about 200–300 mg plant sterols per day, but vegetarians may consume up to 500 mg plant sterols daily. Higher consumption of whole grains such as wheat, barley, and oats will increase plant sterol intake and potentially contribute to lowered blood cholesterol in humans.

Whole grain wheat and barley contain about 2.5–3% lipids and whole grain oats nearly 7.5%. About 75% of these grain lipids are unsaturated, with nearly equal amounts of oleic and linoleic acids, and 1–2% of linolenic acid. In absolute terms, there are 2 g of unsaturated lipids/100 g whole wheat and 5.5 g for whole grain oat. These 2 unsaturated fatty acids are known to lower serum cholesterol, and are suggested to be important components of a heart-healthy diet. Individually, oleic and linolenic acids are associated with lowering of total and LDL-cholesterols.[62] Among the cereal bran lipids, rice and oat bran lipids have been shown to exhibit a cholesterol-lowering effect.[63] Gerhardt and Gallo[63] studied moderately hypercholesterolemic (5.95–8.02 mmol/L), nonsmoking, non-obese adults in a 6‐week, randomized, double-blind, non-cross-over trial. To three groups, 84 g/d of a heat-stabilized, full-fat, medium-grain rice bran product (n = 14), oat bran product (n = 13), or rice starch placebo (n = 17) were added to their usual low-fat diet. Results showed that serum cholesterol decreased significantly (P ≤ 0.05) by 8.3 ± 2.4% and 13.0 ± 1.8% in the rice bran and oat bran groups, respectively, but there was no change in the rice starch group. The change in cholesterol was mainly due to LDL-C, which decreased by 13.7 ± 2.8% in the rice bran group and 17.1 ± 2.4% in the oat bran group (P ≤ 0.05). Serum apoB decreased proportionately, and the LDL-C:HDL-C ratio decreased significantly in both the rice bran and oat bran groups, indicating a lowered risk for cardiovascular disease.[63]

FLAVONOIDS

Flavonoids are present in almost all plants and are known to possess anticarcinogenic, anti-inflammatory, and anti-allergic properties. The most important flavonoids are quercetin, kaempferol, myricetin, and chrysin.[64] Cereals have only small quantities of flavonoids, except that barley contains measurable amounts of catechin and some di- and tri-procyanidins.[65]

FUNCTIONAL FOODS FROM CEREAL GRAINS

Efforts for new product development are being directed by the food industry towards the newly emerging area of functional foods, primarily to meet consumer's demand for healthier foods. For this purpose, cereals such as wheat, oat and barley, as well as their constituents offer unlimited opportunities for the production of functional foods. Many functional foods can be produced from these cereals, however, we only discuss a few important products (pan bread, flat bread, buns, cookies, extruded snacks, and breakfast cereals) in this article.

BAKED GOODS, BREAKFAST CEREALS, AND PASTA PRODUCTS

Due to an ever increasing demand for healthier foods, the baking industry is directing its R&D efforts towards functional foods and functional food ingredients. Cereals offer an attractive alternative for the production of various functional foods such as bread, buns, cookies, breakfast cereals, and snack bars. Various beneficial effects of cereals, as documented previously in the section of this paper “Phytochemicals in Cereals,” can be exploited for the design of novel cereal foods—especially the prebiotic foods. Cereals can be used as fermentation substrates for the growth of probiotic microorganisms.[21] The water soluble fiber, such as beta-glucans, pentosans, oligosaccaharides, and resistant starch present in cereals, can serve as prebiotic foods. Separation of grain fractions rich in these chemical constituents is possible according to the knowledge of their distribution in grains, as well as with the help of various processing technologies such as milling, sieving, air classification, debranning, or pearling. Some of the cereal grain constituents, especially starch (and its derivatives, such as modified starches, dextrins, etc.) can be used as encapsulation materials for probiotics in order to improve their stability during storage, handling, and distribution, and to enhance their viability during passage through the adverse conditions of the human gastro-intestinal tract. Baked products made with oats not only offer a higher satiety value, but they have also been shown to lower blood cholesterol levels in human subjects.[66–67] Pan bread made with added gluten and transglutaminase has been reported to be softer and springy in texture than the oat bread, and these sensory textural characteristics correlated well with the texture and microstructure measured instrumentally.[68]

Psyllium husk, an excellent source of soluble fiber, contains more than 8 times the soluble fiber of the oat bran, but it is difficult to incorporate the required amounts of psyllium into a single serving of a food product, because of its considerable gelling and water-absorbing capacity. Psyllium has been found to significantly lower total cholesterol and low density cholesterol (LDL) in humans.[69] To achieve the maximum serum cholesterol lowering effect of psyllium, it has been recommended that psyllium must be mixed with cereal foods rather than eating it alone.[70] The addition of psyllium (up to a 5% level, on dry basis) to straight-grade flour (WF) and whole wheat flour (WWF) improved the objective texture and sensory quality without adversely affecting the crumb color of Arabic flat bread (pita bread) in the laboratory, as well as during pilot scale production in a commercial bakery.[71] The sensory evaluation data have indicated that psyllium husk, when used either in WF or WWF could produce high-fiber pita bread, which is not only lighter in crumb color and softer in texture, but also is more acceptable to the consumers.

Psyllium has been found to significantly lower total cholesterol and low density cholesterol in humans.[72–75] Because of this reason, psyllium has been investigated for use in a number of cereal based products like breads, cakes, cookies, breakfast cereals, pasta, and soon.[75–81] Ahluwalia, Kaur, and Sidhu[82] have added psyllium at various levels to prepare bread, cake, and cookies. In bread, they observed higher water absorption but a lower specific volume. However, in cakes and cookies, the specific volume and spread ratio did not differ significantly. The panelists did not detect differences in sensory characteristics between samples of control baked goods and those containing psyllium.[82]

Preparation of sour dough based baked products have been investigated to improve their palatability as well as nutritional value. Lopez, Krespine, Guy, Messager, Demigne, and Remesy[83] have reported enhanced phytate breakdown (nearly 90%) with the use of sour dough, which also improved magnesium and phosphorus solubility through acidification by the sour dough process. Improved phytate-phosphorus release and iron dialyzability have also been reported in whole-wheat bread with phytase and citric acid supplementation.[84]

Barley is another important cereal grain that can be used in developing functional baked products. Barley breads made with various proportions of whole wheat flour have been shown to improve glucose tolerance, lower LDL cholesterol and improve sensory characteristics.[85–90] The hull-less barley holds a special promise to produce a variety of functional foods such as flat bread, pan bread, cookies, extruded snacks, and breakfast cereals. Whole grain oat cereal consumption has been reported to reduce the need for antihypertensive medication, lower total as well as LDL cholesterol, and improve fasting blood glucose levels.[91] The largest amounts of β-glucan are reported in barley (3–11%) and oats (3–7%), with lower amounts in rye (1–2%) and wheat (< 1%), and these values depended on cultivars, environmental factors, and the anatomical parts.[92]

FUTURE RESEARCH NEEDS

Consumer interest in functional foods has skyrocketed in the last 15 years due to a number of key factors such as growing health awareness, changes in food regulations, and overwhelming scientific information highlighting the critical link between diet and health. Although a number of new functional foods based on various commodities are now appearing in the market, cereals hold a prominent place in this new market. Because whole cereal grains are rich in many phytochemicals such as dietary fiber (e.g., beta-glucan), resistant starch, antioxidant nutrients (e.g., tocotrienols and choline) vitamins, minerals, lignans, phytic acid, and phenolic compounds, efforts are being made to develop a number of functional foods based on these whole grains.

CONCLUSIONS

In spite of a large number of available publications in this area, additional work is necessary to confirm the health benefits of these whole grain phytochemicals, develop suitable processing techniques to improve the eating quality of whole grain products, and to educate consumers about the expected benefits of consuming such functional foods. The following issues need to be examined in the future: (i) the effect of processing techniques on the retention of favorable properties of various phytochemicals in the finished products; (ii) the health promoting or disease preventing characteristics, and the therapeutic potential of these phytochemicals; (iii) the changes in the concentration of these phytochemicals in various milling fractions of the whole grains; (iv) the identification of their safety limits to avoid health risk of over consumption; (v) the side effects likely to show up with higher intake of these phytochemicals; (vi) the effect of higher amounts of phytochemicals on the taste, texture, and appearance of formulated products; (vii) the effectiveness of these phytochemicals either as singly or in combination; (viii) the use of cereal grains as prebiotics to selectively stimulate the growth of lactobacilli and bifidobacteria present in the colon, and (ix) the possible use of these phytochemicals as future intravenous components as the “green parenteral.” The development of various functional foods based on whole grain cereals is a challenging task. However, the invention of newer technologies for cereal processing to improve their use and health potential, as well as the consumer acceptability of these products, should be the focus area that needs the utmost attention from the cereal technologists in the future.

ACKNOWLEDGMENT

The authors express their gratitude to Dr. Sana'a BuHamra, Dean, College for Women, Kuwait University, for her support and encouragement to prepare this review paper.