Cereals and Pulses

Nutraceutical Properties and Health Benefits

Liangli L. Yu, Rong Tsao, Fereidoon Shahidi, Liangli L. Yu, Rong Tsao, Fereidoon Shahidi

• Editorial: Wiley-Blackwell
• Año: 2012
• ISBN:
  9781118229460
• Edición: 1
• Categoría: Tecnología e ingeniería
• Categoría: Ciencia de los alimentos

Cereal and pulse crops are staple foods that provide essential nutrients to many populations of the world. Traditionally, whole grains were consumed but most current foods are derived from refined fractions of cereal and pulse crops. Consumption of processed or refined products may reduce the health benefits of food. In wheat-based processed foods, for example, the removed 40% of the grain (mainly the bran and the germ of the wheat grain) contains the majority of the health beneficial components. These components, particularly non-essential phytochemicals such as carotenoids, polyphenols, phytosterols/ stanols, and dietary fibers, have been shown to reduce the risk of major chronic diseases of humans, such as cancer, cardiovascular diseases, and Parkinson's disease.

Such bioactives are therefore good candidates for ingredients of nutraceuticals and functional foods. There are many factors that can affect the bioactive content of cereal and pulse-based food ingredients, including genetics, growing and storage conditions, post-harvest treatments, food formulation and processing. All of these factors ultimately affect human health and wellness. Bioavailability is also important for these compounds for exerting their protective roles.

Cereals and Pulses: Nutraceutical Properties and Health Benefits provides a summary of current research findings related to phytochemical composition and properties of cereal and pulse crops. The nutraceutical properties of each major cereal and pulse are discussed. Coverage of cereals and pulse crops includes barley, oats, rice, rye, corn, adlay, wheat, buckwheat, psyllium, sorghum, millet, common beans, field peas, faba beans, chickpea, lentil and soybeans. Chapters for each crop discuss methods to improve crop utilization, nutraceutical components and properties, bioactive compositions, antioxidant properties, beneficial health effects, disease prevention activities, and areas for future research. Also included are two chapters that examine the beneficial health properties of dietary fibers and antioxidants. Edited and written by an international team of respected researchers, this book is a reference guide for scientists working in food ingredients, food product research and development, functional foods and nutraceuticals, crop breeding and genetics, human nutrition, post-harvest treatment and processing of cereal grains and pulses. It will enable them to effect value-added food innovation for health promotion and disease risk reduction.

1 Cereals and pulses – an overview

Rong Tsao, Liangli (Lucy) Yu, and Fereidoon Shahidi

1.1 Introduction

For thousands of years grains and pulses have been produced and consumed as staple foods. Bread, noodles, porridge, breakfast cereals, and other forms of food made from wheat, oats, barley, rice, corn, lentils, chickpeas, and soybean (and other dried seeds) are found in all cultures and cuisines around the world. Many of these foods continue to be home prepared, however, large amounts of the staple foods today, particularly in the industrialized countries, are also made commercially. The global market for breakfast cereals alone was $24.5 billion in 2008, and it is estimated to grow by roughly 17.1% to a total value of $28.7 billion by 2013 (Datamonitor, 2009).

The same report also showed that ready-to-eat cereals dominated, having an 87.8% share of the global breakfast cereals market. America leads the global breakfast cereals market, accounting for 64.9% of the market’s value, according to the same report. However, processing may reduce the health benefits of food and this depends entirely on the form in which the products are consumed. Most of the wheat-based foods, including bread, noodles and pasta, and cookies, are made from bleached white flour (60% extraction). What is more important is that the 40% removed grain, mainly the bran and the germ, contains the majority of the health beneficial components.

Cereal grains and leguminous seeds contain myriad components that are important and essential to human health. The macro-nutrients, carbohydrates, proteins, and fats serve as a rich source of energy and contain many essential nutrients such as vitamins, amino acids, and fatty acids. However, in recent years, some of these and other minor components have been found to play important roles beyond satisfying basic nutritional requirements. Studies have shown that dietary fibers and certain phytochemicals can be key to health maintenance and disease risk reduction. Intakes of dietary fibers and phytochemicals have been associated with reduced risk of cancer, cardiovascular disease, diabetes, chronic inflammation, neural degeneration, and other chronic ailments and illnesses. These bioactives are, therefore, good candidates as ingredients for nutraceuticals and functional foods.

Meanwhile, many factors can affect the composition and the potential health benefits of foods rich in these bioactives throughout the value chain. Genetics, growing and storage conditions, post-harvest treatments, food formulation, and processing can all affect the content of these bioactives in cereal- and pulse-based food ingredients, and related foods and food supplements, ultimately affecting human health and wellness. This monograph focuses on the chemical and nutraceutical compositions, and potential health beneficial properties, of commonly consumed cereals and legumes. The effects of growing conditions, post-harvest treatments, and food processing and formulation on nutraceutical properties of the cereals and legumes are also covered. In addition, the mechanisms involved in rendering the beneficial effects of cereal and legume components are discussed.

1.2 Chemistry and nutraceutical compositions

Intact kernels of grains or seeds contain three major parts: germ/embryo, endosperm/cotyledon, and bran/seedcoat. It is also important to know that most of the nutrients, including dietary fibers and polyphenols, are found in the germ and bran or seedcoat, therefore to receive maximum health benefits, food products made from whole grains or pulses are preferable. Refined grains and pulses often have the germ and the bran or seedcoat removed, thus important dietary fibers, vitamins, minerals, and bioactive phytochemcials are lost; although in countries such as the US and Canada manufacturers are required to enrich white flour with several vitamins and iron.

Phytochemicals are plant-originated secondary metabolites that possess various biological activities. These natural products can be categorized into different chemical classes (Liu, 2004; Tsao, 2010). Cereal grains and pulses are a rich source of bioactive phytochemicals. While polyphenols and carotenoids are perhaps the most studied phytochemicals, particularly for their antioxidant activities, other groups such as phytosterols and saponins are major contributors to the health benefits of cereal grains and pulses.

Food compositions can be altered by targeted breeding. Grains and pulse crops can produce significantly more or less of certain components, for example, soybeans with low, medium, and high isoflavone contents have been developed and formulated into functional soy-breads that contain different levels of naturally occurring isoflavones (Shao et al., 2009). Environmental factors such as growing season, soil type, temperature, and agronomic practices (organic vs. conventional) have also been found to significantly affect the phytochemical compositions (Zhou et al., 2005). Phytochemicals such as polyphenols and carotenoids are relatively unstable under high temperature, thus food processing, such as production of breakfast cereals, can lead to loss of important bioactive compounds that are key to human health (Slavin et al., 2000; Muzhingi et al., 2008).

1.3 Potential health beneficial effects

Dietary fibers and phytochemicals are important components of a healthy diet. Dietary fibers, particularly soluble fibers such as β-glucans from barley and oats, have been found to significantly reduce the total and LDL (low-density lipoprotein) cholesterol levels (Brown et al., 1999; Chapters 2 and 3 in this volume); and the effect was discovered to be related to the physicochemical properties such as the molecular weight of β-glucan (Wolever et al., 2010). Dietary fiber of rice bran also reduces LDL cholesterol, as discussed in Chapter 5. On the other hand, results of epidemiological studies of dietary fiber and cancer risks have not been consistent. For example, examining the consumption of dietary fiber and the risk of colorectal cancer, a recent Japanese study found that total, soluble, and insoluble dietary fibers were not measurably associated with overall risk or subsite-specific risk of colorectal cancer (Uchida et al., 2010). However, the same study suggested a decreased risk of distal colorectal cancer associated with rice consumption. Nevertheless, other studies have indeed shown a positive correlation between the consumption of dietary fibers and cancer risks. Howe et al. (1992) showed convincingly that intake of fiber-rich foods was inversely related to risk of cancers of both the colon and rectum. Among the 13 case–control studies, 12 showed significant correlation between dietary fiber intake and the decrease of risk of both left- and right-sided colon and rectal cancers, for men and women, and for different age groups, but no associations were seen for the intakes of vitamin C and β-carotene (Howe et al., 1992). A more recent study concluded similarly that the intake of dietary fiber was inversely associated with colorectal cancer risk. The authors also suggested that methodological differences (i.e. study design, dietary assessment instruments, definition of fiber) may account for the lack of convincing evidence for the inverse association between fiber intake and colorectal cancer risk in some previous studies (Dahm et al., 2010). Dietary fibers from pulse crops may also contribute to the reduction of LDL cholesterol and the risk of cancer, however, more research needs to be done in this area. Dietary fibers from other food crops including psyllium and sorghum are also known for similar health benefits (Chapters 11 and 12, respectively). Other forms of carbohydrates, such as resistant starch in corn (Chapter 7), also play important roles in alleviating health risks. The health properties of dietary fiber preparations and the potential molecular mechanisms involved in their beneficial actions are summarized in Chapter 18. In general, psyllium, oats, barley, and several edible legumes are important dietary sources of soluble fibers, while bran of wheat and corn are good sources of insoluble fiber. Soluble fibers may absorb moisture in the GI (gastrointestinal tract) track and form viscous fluid or gel, which may trap lipid and bile acids reducing their bioavailability and total energy intake. They may also be fermented in the large intestine and form short chain fatty acids, which can reduce the local pH and enhance the movement of intestinal contents. Such effects may lead to reduced absorption of energy and toxins, as well as changes of the microorganism profile in the large intestine. High intake of dietary fibers may reduce the risk of several human chronic diseases, such as cardiovascular diseases, diabetes, and colon cancer (Chapter 18).

While dietary fibers are an important ingredient contributing to the health benefits of cereal grains and pulses, ample evidence exists that phytochemicals may play greater roles. Many different classes of phytochemcials have been identified and their specific bioactivities reported. The major phytochemcials that have shown health benefits include various phenolic compounds, carotenoids, saponins, and phytosterols. Many of these secondary metabolites provide chemical defense against invading insects or microorganisms, or participate in wound healing in the plants.

Phenolic compounds, including the phenolic acids and flavonoids are responsible for the total antioxidant activity of cereals and pulses (Chapter 19). The majority of the phenolics are found in the bran or seed coat of the grains, therefore, consumption of whole grain and intact seed-based foods is of greater benefit. Diets rich in phenolics have been linked to the reduction of several chronic diseases, particularly those caused by oxidative stress such as cancer, cardiovascular diseases, diabetes, and inflammatory illnesses. However, additional roles of phenolic compounds, particularly flavonoids, have been identified in recent years. In addition to the direct antioxidant activities, flavonoids, for example, have been shown to modulate cell signaling pathways at physiological concentrations way below those required to impact cellular antioxidant activities. Modulation of cell signaling pathways by flavonoids could help prevent cancer by stimulating phase II detoxification enzyme activity and by inhibiting proliferation and inducing apoptosis. Inhibition of biomarkers such as NFkB of inflammation and increase of the endothelial nitric oxide synthase (eNOS) activity may help prevent cardiovascular diseases.

The antioxidant activity of the phenolics has been associated with many chronic diseases. Cinnamic acid and its derivatives, particularly ferulic acid, are the main phenolic acids in cereal grains (Zhou et al., 2005). Phenolic acids are found mostly in the bran, and the majority may exist in conjugated and bound forms (Liyana-Pathirana and Shahidi, 2006; Kim et al., 2006; Chandrasekara and Shahidi, 2010; Chapter 19). Cereal grains are also the major dietary source of lignans, a group of polyphenols that play important roles in human health, particularly as precursors of mammalian lignans. These compounds are mostly found in the bound form, thus are not normally extractable by organic solvents (Chapters 6 and 9). Flavonoids, mainly flavones and flavonols, have been found in cereal grains. Apigenin, kempferol, and quercetin glycosides are major flavonoids, however, anthocyanins contribute significantly to the total flavonoid content in dark colored grains such as purple corn (Chapter 7). Catechins have also been identified in grains such as buckwheat (Chapter 10). Sorghum and millet, with their unique drought-resistance and high level of polyphenols, are considered important to combat the continuously increasing health problems of obesity, diabetes, cardiovascular diseases, and cancer. Sorghum is unique among cereals with its high content of condensed tannins that are oligomeric and polymeric flavonoids. These proanthocyanins are strong antioxidants and considered key for lowering risks of several chronic diseases (Chapter 12). Seed coat of pulses is also a good source of flavonoids (Chapters 14 and 15). Isoflavones, a subgroup of flavonoids, are only found in soybean and other legumes. Isoflavones and lignans are phytoestrogens, therefore, in addition to other biological activities, their role in hormone-related diseases such as breast cancer and osteoporosis is also important (Chapters 17). Other legumes such as pulse crops have been studied in recent years and efforts have been made to determine the bioactives and their relationship with health benefits (Chapters 14 and 15).

Carotenoids are critical to the photosynthesis of plants, however, many of these compounds, such as β-carotene, are also important to humans as vitamin A precursors. In cereals and pulses, while many carotenoids have been identified, zeaxanthin and lutein are worthy of special mention. These two non-vitamin A precursors, found mainly in corn and other cereal grains such as wheat, are not only strong antioxidants, but can also inhibit cancer cell proliferation and prevent cell mutation. These compounds are especially critical to the health of the eye (Chapter 7).

Other phytochemicals, such as phytates, saponins, and phytosterols, have also been found to contribute to the potential health benefits of cereals and pulses. Policosanols and lactams are unique bioactives found in a minor cereal crop adley, among other commonly found phytochemicals that showed various health benefits (Chapter 8). D-chiro-inositol and fagopyritols in buckwheat have also been found to benefit diabetics (Chapter 10). However, it is generally understood that these and all other above-discussed active components play an assorted role in various health problems, as pointed out in Chapter 18. Their composition and specific roles can be found in different chapters of this book. It is our hope that this book offers a focused discussion of cereals and pulses as important contributors to health, and how we can improve the quantity and quality of their functional components in the diet throughout the value-chain, i.e. breeding, production, postharvest storage, and food processing. Reviews on the chemistry, biochemistry, and mechanisms of action of the bioactives, including dietary fibers and the various phytochemicals, will also provide insights into future research.

References

Brown, L., Rosner, B., Willett, W.W., and Sacks, F.M. (1999) Cholesterol-lowering effects of dietary fiber: A meta-analysis. American Journal of Clinical Nutrition, 69: 30–42.

Chandrasekara, A. and Shahidi, F. (2010) The content of insoluble bound phenolics in millets and their contribution to antioxidant capacity. Journal of Agricultural and Food Chemistry, 58: 6706–6714.

Dahm, C.C., Keogh, R.H., Spencer, E.A., Greenwood, D.C., Key, T.J., Fentiman, I.S., Shipley, M.J., Brunner, E.J., Cade, J.E., Burley, V.J., Mishra, G., Stephen, A.M., Kuh, D., White, I.R., Luben, R., Lentjes, M.A., Khaw, K.T., and Rodwell Bingham, S.A. (2010) Dietary fiber and colorectal cancer risk: a nested case-control study using food diaries. Journal of the National Cancer Institue, 102: 614–626.

Datamonitor. 2009. Breakfast Cereals: Global Industry Guide, http://www.fastmr.com/prod/47026_breakfast_cereals_global_industry_guide.aspx. Howe, G.R., Benito, E., Castelleto, R., Cornée, J., Estève, J., Gallagher, R.P., Iscovich, J.M., Deng-ao, J., Kaaks, R., Kune, G.A., Kune, S., L’bbe, K.A., Lee, H.P., Lee, M., Miller, A.B., Peters, R.K., Potter, J.D., Riboli, E., Slattery, M.L., Trichopoulos, D., Tuyns, A., Tzonou, A., Wittermore, A.S., Wu-Williams, A.H., and Shu, Z. (1992) Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. Journal of the National Cancer Institute, 84: 1887–1896.

Kim, K.H., Tsao, R., Yang, R., and Cui, S.W. (2006) Phenolic acid profiles and antioxidant activities of wheat bran extracts and the effects of hydrolysis conditions, Food Chemistry 95: 466–473.

Liu, R.H. (2004) Potential synerg...