More than 2000 years ago Hippocrates said: ‘Let food be your medicine and medicine be your food.’ Sears (2000) stated that food is the most potent medicine of all. At no time have these statements been more relevant than at the dawn of the 21st century. For the first time in 10,000 years, since agriculture first fuelled human development, what we eat is being associated with deaths due to chronic diseases worldwide, especially in high-income countries. Of all the diseases recorded in 2001, 46% were chronic (including cardiovascular disease, diabetes, cancers and obesity). These chronic dis- eases accounted for 60% of all deaths in the world, but are largely preventable by improvements in diet and exercise (WHO/FAO, 2003). The proportion of chronic dis- eases is expected to increase from 46% to 57% by 2020 and have already started to occur at younger ages (WHO/FAO, 2003). As a result of industrialization, urbanization and globalization of food markets, we are now facing an epidemic of obesity and a danger that some children will die at an earlier age than their parents (Jadad, 2005).
Plant foods contain many constituents that are non-nutritive in nature, yet may promote good health. The presence of many different types of proteins and other smaller molecules, including alkaloids, isoflavones, polyphenolics and a variety of oligosaccharides, make pulse seeds unique. Experimental evidence has demonstrated the beneficial activity of pulse components in the prevention and treatment of various diseases. This has prompted a reappraisal of pulses in the diet recently. By and large, these results strongly support the claim that a diet that includes a regular intake of pulses, including chickpea, is one of the ways to maintain and improve health.
Carbohydrates
All carbohydrates are not created equal. Some break down quickly dur- ing digestion and can raise blood glucose to dangerous levels. These are the
foods that have high glycaemic indexes (GIs). Other carbohydrates break down more slowly, releasing glucose gradually into our bloodstream and are said to have low GIs. GI is defined as a measure of the blood glucose response to carbohydrates within a food as a percentage of the response to an equivalent carbohydrate dose of glucose (Monro and Williams, 2000).
Diabetes is a chronic disease where the body either does not produce insu- lin or does not respond to insulin properly. Insulin is usually released into our bloodstream after a meal to convert glucose into energy, thereby reducing our blood glucose levels. The inability of diabetics to produce or use insulin causes their blood glucose levels to rise dangerously after eating; the higher the food’s GI, the more dangerous the potential increase in blood glucose levels.
Legumes generally have a GI of less than half that of white and wholemeal bread (Kozlowska et al., 2001) and chickpea probably has the lowest GI among the food grains. FAO/WHO listed chickpea with the GIs of 44 (raw) and 47 (canned) compared to white bread at 100 (FAO/WHO, 1998). Mendosa (2005) reported raw chickpea as having a GI of 7–11 compared to more than 100 for white bread and potatoes. In addition, Nalwade et al. (2003) found that boiled chickpea had a low GI of 21.45, compared to boiled lentil (27.63), boiled rice (61.18) and bread (76.55). It would therefore be beneficial to include chickpea in the diets of diabetics.
Other health-beneficial carbohydrates include oligosaccharides and resistant starch, which can serve as prebiotics (Guillon and Champ, 2002).
Prebiotics stimulate growth and activity of beneficial bacteria in the gastroin- testinal tract (e.g. Bifidobacterium and Lactobacillus) over harmful bacteria (e.g.
Salmonella spp., Helicobacter pylori,Clostridium perfringens). More than half of the ‘functional foods’ on the Japanese market contain prebiotic oligosac- charides as the active component, with the aim of promoting favourable gut microflora to improve human health (FAO/WHO, 1998).
Fibre is known to decrease the bioavailability of many mineral components of the diet, but it also has many advantages. High-fibre diets decrease disorders of the bowel such as constipation, diverticulitis and cancer. This is achieved through increased faecal bulk (diluting potential carcinogens, improving bowel muscu- lature and decreasing the time potential carcinogens spend in the bowel) and through bacterial fermentation (producing short-chain fatty acids such as acetic, propionic and butyric acids), which stimulate growth of healthy colonic epithe- lial cells and promote death of bowel tumour cells (Gurr and Asp, 1994). The by-products of this reaction are gases (carbon dioxide, hydrogen and methane).
High-fibre diets also lower the faecal pH, thereby aiding in the excretion of pro- tein metabolites, which are potent carcinogenic substances (Binghams, 1990).
Fibre in the diet increases bile acid excretion in the bowel, which can reduce blood lipid levels (useful in the prevention and treatment of cardio- vascular disease) and beneficially influence cholesterol metabolism (Vahouny et al., 1988; Wolever and Miller, 1995; Vanhoof and Schrijver, 1997). Studies have shown that replacing animal products with legumes (such as in vegetar- ian diets) can reduce the incidence of cancers of the digestive tract through decreased saturated fat and increased dietary fibre in the diet. Cassidy et al.
(1994) examined food consumption in 12 countries and found an inverse
correlation between colorectal cancer incidence and starch or NSP intake, and a positive association with protein and fat.
A high dietary intake of NSP or dietary fibre has been recognized by the WHO as being protective against obesity (WHO/FAO, 2003). Low GI foods may also play a role, although more studies are needed to prove this. In addi- tion, a high intake of NSP has been shown to reduce blood glucose and insulin levels, and is likely to be protective against diabetes (WHO/FAO, 2003). A minimum daily intake of 20 g NSP is recommended. Chickpea is rich in NSP with a low GI. Approximately 40 g of chickpea is sufficient to satisfy the daily NSP recommended by the WHO (Table 5.1).
Phenolics
Phenolics are one of the most numerous and diverse of all the plant metabo- lites. They are an integral part of both human and animal diets and can range from simple molecules, such as phenolic acids, to highly polymerized com- pounds, such as tannins. The basic phenolic backbone consists of an aromatic ring substituted with one or more hydroxyl units. The most common phenolics (found in all vascular plants) are the polyphenolics and lignins (Shahidi and Naczk, 1995). Hundreds of new polyphenolic structures are being discovered every year (Williams and Grayer, 2004; Martens and Mithöfer, 2005). The main classes of polyphenolic compounds are classified by their chemical structures.
They are simple phenols, benzoquinones, phenolic acids, acetophenones, phenylacetic acids, hydroxycinnamic acids, phenylpropenes, coumarins, chro- mones, naphthoquinones, xanthones, stilbenes, anthraquinones, flavonoids, lignans and lignins (Bravo, 1998). In legumes, the main phenolics in the seed are phenolic acids, flavonoids and lignans.
Historically, plant polyphenolics interested scientists for their contribution to plant physiology, including their role in growth and reproduction, pigmenta- tion and provision of resistance to some pathogens, predators and environmen- tal conditions. Polyphenolics also proved to be valuable in several industrial applications, such as the production of tanning solutions, paints, paper, cos- metics and rubber coagulation. From a nutritional point of view, polyphenolics were traditionally considered ANFs due to the adverse effects of tannins bind- ing with macromolecules (such as dietary protein, carbohydrate and digestive enzymes), thereby reducing food digestibility and bioavailability. Polyphenolics have also been used in the food industry as natural food colorants, preservatives and in the clarification of wine, beer and fruit juices. Polyphenolics are also responsible for the taste sensations of astringency and bitterness, thus influenc- ing the sensory and nutritional qualities of food. Oxidation of polyphenolics during storage or processing often results in changes in the organoleptic prop- erties of food. For example, the desirable taste of tea develops from polyphe- nolic oxidation during processing, and in red wine, modification of astringency with ageing. Conversely, the enzymatic and non-enzymatic browning reactions of phenolic compounds are responsible for the formation of undesirable colour and flavour in fruits and vegetables. In the case of chickpea, prolonged storage
under high temperature and humidity will cause browning reactions of the phenolic compounds in the seed coat.
Only recently has interest in polyphenolic compounds, mostly the fla- vonoids, surfaced due to their antioxidant capacity and potential benefits to human health, such as in the treatment and prevention of cancer, cardiovas- cular disease, hypertension, hypercholesterolemia, atherosclerosis, bacterial and viral infection, diarrhoea, ulcers, inflammation and allergies (Bravo, 1998;
Martens and Mithöfer, 2005).
Polyphenolics are common in most plant foods (vegetables, cereals, legumes, fruits, nuts, etc.), with wide variations in content influenced by genetic and environmental factors, agronomic practices and storage conditions.
Legumes generally have higher polyphenolic contents than cereals, which con- tain <1% of polyphenolic compounds. In pulses, the seed coat usually contains the majority of polyphenolic compounds. Hence, desi types will have a higher concentration than kabuli types due to the larger seed coat content. Singh and Jambunathan (1981) found that ~75% of the polyphenolic content was present in the seed coat of desi types. In addition, the darker varieties of legumes usu- ally contain higher amounts of polyphenolics, such as red kidney beans, black beans (P. vulgaris) and black gram (Vigna mungo). This also holds true within legume species, so that desi chickpea will generally have higher polyphenolic contents than the kabuli variety, and darker desi seeds will generally contain more than lighter-coloured seeds. Desi and kabuli chickpea contain 0.84–6.00 and 0.02–2.20 mg/g polyphenols, respectively (Table 5.4).
Phenolic acids
Kaushiket al. (1996) and Sosulski and Dabrowski (1984) analysed the phenolic acids in cotyledon and seed coat fractions of desi and kabuli types, respec- tively. They used different methods and came up with different answers (Table 5.6). Large variations between desi varieties were also observed.
Flavonoids
Flavonoids are the most common and widely distributed group of plant pheno- lics, with more than 9000 compounds described (Martens and Mithöfer, 2005).
There are 13 classes of flavonoids (Bravo, 1998): chalcones, dihydrochalcones, aurones, flavones, flavonols, dihydroflavonols, flavanones, flavanols, flavan- diols (also called leucoanthocyanidin), anthocyanidins, isoflavonoids, bifla- vonoids and proanthocyanidins (also called condensed tannins). Their basic structure is derived from diphenylpropanes. Flavonoids commonly occur as glycoside derivatives in plants but can also exist as free monomers.
Anthocyanins, isoflavoids (isoflavones, pterocarpans), flavones (in aer- ial parts), flavondiols and tannins have been detected in chickpea seeds (Harborne, 1994; Bravo, 1998). The flavone 3,7,4’-trihydroxyflavanone was named ‘garbanzol’ after its discovery in chickpea (Kühnau, 1976). In addition, it is plausible that chickpea seeds may contain flavonols, as they are precursors to anthocyanins. Most flavonoids are of relatively low molecular weight and are soluble to some degree. However, others can be essentially unextractable, linked to cell wall components such as polysaccharides and lignin. There is
alue121 Table 5.6. Phenolic acid composition of desi and kabuli chickpea cotyledons and seed coats.
Desi whole seed Kabuli whole seed
Cotyledons Number of Number of
Parameter Unit Minimum Maximum cultivars References Minimum Maximum cultivars References
Gallic acid mg/g 0.0 22.9 6 1 – – – –
Protocatechuic acid mg/g 0.0 22.5 6 1 – – – –
p-hydroxybenzoic acid mg/g 16.3 39.4 6 1 – 0 1 2
Chlorogenic acid mg/g 0.0 31.3 6 1 – – – –
Vanillic acid mg/g 0.0 0.0 6 1 – – – –
Caffeic acid mg/g 0.0 0.0 6 1 – – – –
p-coumaric acid mg/g 0.0 0.0 6 1 – 0
Ferulic acid mg/g 0.0 0.0 6 1 – 43 1 2
Syringic acid mg/g – – – – – 52 1 2
Total phenolic acids mg/g 16.3 98.1 6 1 – 95 1 2
Seed coat
Gallic acid mg/g 0.0 25.9 6 1 – 0.0 1 2
Protocatechuic acid mg/g 0.0 15.0 6 1 – 0.0 1 2
p-hydroxybenzoic acid mg/g 0.0 21.3 6 1 – 8.0 1 2
Chlorogenic acid mg/g 0.0 0.0 6 1 – – – –
Vanillic acid mg/g 0.0 – 6 1 – – – –
Caffeic acid mg/g 0.0 – 6 1 – – – –
p-coumaric acid mg/g 0.0 22.8 6 1 – 3.0 1 2
Ferulic acid mg/g 0.0 0.0 6 1 – 0.0 1 2
Total phenolic acids mg/g 16.3 74.4 6 1 – 11.0 1 2
Total phenolic acids in seed mg/g 42.2 172.5 6 1 – 106 1 2 1. Kaushik et al. (1996); 2. Sosulski and Dabrowski (1984).
very little literature on the polyphenolic composition of chickpea. Most of the literature has focused on tannins in tea, anthocyanidins in wine and isoflavo- noids in soybean.
ANTHOCYANINS Anthocyanins are water-soluble plant pigments often responsible for the orange to red (sometimes blue, violet or magenta) colour of flowers, fruits and seeds of higher plants. Anthocyanins are the glycosides of anthocyanidins (e.g. pelargonidin, malvidin, cyanidin) and play an important role in pollinator attraction and seed dispersal. Most of the literature focuses on anthocyanins of flowers and more recently on red wine. Relatively little work has been done on anthocyanins as a dietary component; however, Kong et al. (2003) recently reviewed the literature on the health-promoting benefits of anthocyanins out- lining their antioxidant, anti-inflammatory, anti-oedema, anti-ulcer and anti- tumour activities. Hence, anthocyanins may play a role in the prevention of coronary heart disease, inflammatory diseases and some cancers.
PHYTOESTROGENS Phytoestrogens are able to mimic the hormone oestrogen and activate or block oestrogen receptors in the body. Several different classes of molecules have been identified as phytoestrogens (Mazur, 1998; Rubio, 2003).
Phytoestrogens are converted by microflora into biologically active compounds that are structurally similar, but not identical, to human oestrogens (Setchell et al., 1981). These hormone-like structures allow phytoestrogens to have oestrogenic activity in animals. Thus phytoestrogen is essentially a functional classification (Ganora, 2003–2005). The plant family most abundant in phy- toestrogens is the Leguminosae.
Dietary phytoestrogens have been found to possess many pharmaco- logic attributes, as they are oestrogenic/anti-oestrogenic, hypocolesterolemic, anti-atherogenic, antioxidative, chemoprotective, antiviral, antibacterial and anti-insecticidal, and have been found to stimulate endothelial cell prolifer- ation and platelet activation (Setchell et al., 1981; Adlercreutz et al., 1991, 2000a,b; Mazur and Adlercreutz, 2000). The perceived beneficial health effects of phytoestrogens include possible prevention or delay of hormone-related cancers (breast, prostate and colon), cardiovascular disease, diabetes, osteo- porosis, inflammation and menopausal symptoms. In addition, they may be beneficial to the immune system and to brain function. Breast cancer is around six times lower in eastern Asia than in the USA, possibly due to higher con- sumption of phytoestrogens through soybeans and other legumes in the former.
The isoflavone intake has been estimated to range from 15 to 200 mg/day in the traditional Japanese diet compared with <1 mg/day in western diets (de Kleijn et al., 2001). In addition, Japanese women excrete 100–1000 times more uri- nary oestrogens than western women (Adlercreutz et al., 1991). Isoflavones, coumestans (coumestrol) and lignans are the most powerful phytoestrogens found in plants. However, not all isoflavones are oestrogenic.
Lignans, although not in the flavonoid class of polyphenolics, are also powerful phytoestrogens. Mazur et al. (1998) examined lignans in chickpea and found that both desi and kabuli types contained significant amounts of the lignan secoisolariciresinol, but no matairesinol (Table 5.4).
ISOFLAVONOIDS Isoflavones are a group of diphenolic secondary metabolites.
Although 22 families of plants produce and accumulate isoflavones, only cer- tain species contain medicinally significant amounts (Dixon, 2001). The best- studied dietary phytoestrogens are the soy isoflavones and the flaxseed lignans.
Chickpea is one of the richest dietary sources of isoflavones, second only to soybean (Mazur et al., 1998). The four most common active isoflavones are diadzein, genistein, formononetin and biochanin A. Biochanin A and for- mononetin are metabolized to genistein and diadzein, respectively, after inges- tion. Diadzein and genistein exhibit strong activity in oestrogen receptor assays.
Soybean has high glycetein, diadzein and genistein contents, whereas chick- pea has high biochanin A content. Wall et al. (1988) found that chickpea seeds contain small amounts of biochanin A, formononetin and diadzein. In addition to diadzein and formononetin, Jaques et al. (1987) previously extracted three other isoflavones from chickpea cotyledons (calycosin 3’-hydroxy-formone- tin, pseudobaptigenin and pratensein) and two isoflavone glycosides (diadzein 7-O-glucoside and formononetin 7-O-glucoside). Mazur et al. (1998) examined phytoestrogens in chickpea seeds recently and found that the major isoflavone type was biochanin A, containing 838 mg/100 g and 1420–3080 mg/100 g in desi and kabuli types, respectively. Chickpea contains much more biochanin A than any other pulse, containing 7–300 times more than the second highest pulse, pigeon pea (C. cajan). The next most abundant polyphenolic was formononetin, containing 215 mg/100 g and 94–126 mg /100 g (desi and kabuli, respectively).
Chickpea seeds also contained smaller concentrations of genistein and diadzein.
Coumestans are another type of isoflavonoid and include the plant steroid coumestrol. Coumestans are thought to have the greatest oestrogenic activity of all the isoflavones. In the study by Mazur et al. (1998), the desi type contained a very small amount of coumestrol, whereas the kabuli type did not.
Isoflavones have been shown to have anticancer properties also (Mathers, 2002). Girón-Calle et al. (2004) showed that an extract containing isoflavones from chickpea had an inhibitory effect on the growth of epithelial tumours with no detrimental effect on healthy epithelial cells.
Tannins
Tannins are compounds of intermediate to high molecular weight and their name originated from their tanning ability. They are also able to form insoluble complexes with carbohydrates and proteins, and the precipitation of salivary proteins is responsible for astringency in tannin-rich foods. In addition, poly- phenolics often form complexes with minerals, reducing intestinal absorption.
For these reasons, polyphenolics (particularly tannins) have traditionally been considered antinutrients and will be described in more detail by Muzquiz and Wood (Chapter 6, this volume). Chickpea seed contains less than 0.04% and 0.09% condensed tannins in kabuli and desi types, respectively (Petterson et al., 1997; Salgado et al., 2001). The total tannin content is also low at 0.12–0.51%
(kabuli) and 0.36–0.72% (desi).
Tannins have recently received some positive attention for the roles they play in health. Many tannins have been found to exhibit chemoprotective, antiviral and antibacterial activity, and may be beneficial in the prevention
and/or treatment of acquired immune deficiency syndrome (AIDS), cardio- vascular disease and various cancers (Hertog et al., 1993, 1995; Khanbabaee and van Ree, 2001). The ability of polyphenolics to chelate with metals can inhibit some reactions that produce active oxygen radicals in the body. In addi- tion, polyphenolics are very effective antioxidants (chelating with free radicals in the same way as they do with minerals), and can retain their free radical scavenging capacity after forming complexes with metal ions (Afanas’ev et al., 1989). This antioxidant activity can continue right through the digestive tract because tannins are not absorbed. Polyphenolics’ protective effect against cardiovascular disease is due to their antioxidant ability inhibiting LDL oxi- dation. Inhibition of starch-degrading enzymes and polyphenolic binding with starch itself can beneficially decrease the glycaemic and insulinemic response to a meal. Similarly, it has been shown that polyphenolic compounds may have beneficial hypocholesterolemic effects by binding with lipids and cholesterol.
Plant sterols
Plant sterols, or phytosterols, are present in small quantities in legume seeds.
They are essential components of plant cell membranes and are most abundant as sterol glucosides and esterified sterol glucosides. Their chemical structure resembles cholesterol; hence they are able to inhibit the absorption of dietary cholesterol in the small intestine. This action can help lower LDL blood cho- lesterol in humans and may help minimize the risk of coronary heart disease.
Plant sterols have also been shown to have anticancer properties (Champ, 2002;
Mathers, 2002). The sterol content of chickpea seeds and flour (besan) is 35 and 39 mg/100 g, respectively (Nutrient Data Laboratory, USDA Agricultural Research Service, 2005). Similarly, Sánchez-Vioque et al. (1998) reported the total sterol content to be 0.04% in defatted chickpea flour, comprising b-sitosterol (83%), campesterol (9%), stigmasterol (6%) and d-5-avenasterol (2%).
Saponins
Chickpea has a higher content of saponins (25–56 mg/g) than soybean and other pulses, with molecular structures that consist of sugars linked to triter- penes (Fenwick and Oakenfull, 1983; Kerem et al., 2005). In plants, saponins appear to help fight infections and microbial invasions. As a dietary compo- nent, saponins have traditionally been classified as ANFs (refer to Muzquiz and Wood, Chapter 6, this volume). However, there are many benefits in consuming saponins as there is some evidence that they may have hypocholesteremic and anticancer properties, stimulate the immune system, ward off microbial and fungal infections, protect against viruses (including human immunodeficiency virus – HIV) and may even act as a spermicide (Thompson, 1993; Ruiz, 1996;
Anderson and Major, 2002; Champ, 2002; Madar and Stark, 2002; Mathers, 2002). Some saponins are 50% sweeter than sucrose, and can therefore be used as healthier, non-caloric sweeteners (Kinghorn and NamCheol, 1997).