Barley for Food and Health: Science, Technology, and Products

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GENETICS AND NUTRIENT COMPOSITION 59 TABLE 4.2 Carbohydrates (g/kg) and Extract Viscosity of Nonwaxy and Waxy Barley Genotypes, Dry Matter Basis Nonwaxy Waxy Item a Hulled Hulless Hulled Hulless Starch 55.9 61.3 51.5 58.5 Sugars b 2.3 2.9 5.0 5.5 Fiber Total dietary fiber 17.0 13.2 19.6 13.8 Soluble dietary fiber 4.4 4.9 5.9 6.3 Arabinoxylans 6.2 4.4 6.7 4.6 Cellulose 3.8 2.1 4.4 1.9 Lignin 2.0 0.9 1.8 0.9 Total β-glucans 4.4 4.7 5.3 6.3 Soluble β-glucans 2.6 2.6 3.2 3.4 Extract viscosity (cP) 2.8 3.1 3.3 4.9 Source: Adapted from Xue (1992). a n = 6 for hulled types and n = 12 for hulless types. b Glucose, fructose, sucrose, maltose, and fructans. Carbohydrates Carbohydrates are described in a number of ways, some of which are quite general and have little meaning or application to foods and nutrition. Broadly speaking, carbohydrates are composed of carbon, hydrogen, and oxygen, but in some instances in nature they are complexed with nitrogenous or lipid compounds. Large-molecular-weight compounds such as starch and cellulose are referred to as complex carbohydrates, as opposed to simple sugars such as glucose, fructose, and sucrose. Complex carbohydrates, which make up the bulk of grain carbohydrates, are generally termed polysaccharides, which in barley and other cereals are divided into starch (soluble polysaccharides) and nonstarch or insoluble polysaccharides. The major nonstarch polysaccharides of barley include mixed linked (1,3)(1,4)-β-d-glucans (β-glucans) and arabinoxylans. These compounds, along with small amounts of (l,4)-β-d-glucan (cellulose), glucomannan, and (1,3)-β-glucan inclusively, are referred to as total dietary fiber (TDF). Carbohydrates as a whole are the largest component of the barley kernel, making up approximately 80% of the total dry matter. Although not a carbohydrate, lignin is generally included as a part of the carbohydrate complex because it is intimately associated with the fiber components, especially cellulose (Table 4.2). Starch Most soluble carbohydrates are deposited and stored within cells in the starchy endosperm tissue during the maturation of the kernel. The largest component
60 BARLEY: GENETICS AND NUTRIENT COMPOSITION of the carbohydrate group is starch, considered a soluble polysaccharide and the major source of energy in barley for food and growth of the new plant after germination. Starch is also the most variable constituent of all nutrients in barley, varying from a low of 45% or less to as much as 65% of the kernel, due primarily to environmental growing conditions. However, certain barley cultivars have 50 to 75% less starch than the average barley, due to incomplete filling of the endosperm. This is a genetically controlled factor that effectively removes a starch-synthesizing enzyme system producing a shrunken endosperm (Eslick 1981; Morell et al. 2003). In one instance the barley is waxy (high amylopectin) (Eslick 1981), and in the other, high in amylose (Morell et al. 2003). The waxy type has been reported to contain high levels of sugars (Hofer 1985; Åman and Newman 1986). Barley starch is composed of two structural types, amylopectin and amylose. Amylopectin is a branched-chain polysaccharide in which α-(1,4)-d-glucose units are branched through α-(1,6)-d-glucose linkages, and amylose is primarily a straight chain of α-(1,4)-d-glucose units (Briggs 1978). Although amylose is generally considered the linear component of starch, there is limited branching in the molecule (MacGregor and Fincher 1993). The side chains have not been characterized completely in barley amylose, but may range in size from four to more than 100 glucose residues (Takeda et al. 1984). Barley amylopectin is a large molecule (Banks et al. 1972; DeHaas and Goering 1972), but despite its large size has a relatively low viscosity in dilute solution compared to that of amylose. Barley amylose molecules are smaller than amylopectin molecules, existing in a random coil structure. Amylose is unstable in aqueous solutions, tending to precipitate or retrograde in dilute solutions and form gels in concentrated solutions (MacGregor and Fincher 1993). In most barley, amylopectin is the major starch type, making up 72 to 78% of the total, with amylose making up the remaining 22 to 28%. Although barley most often contains amylopectin and amylose in the 3 : 1 ratio, certain cultivars contain starch that is 95 to 100% amylopectin, and there are at least three cultivars that contain 40 to 70% amylose as a percentage of the total starch. The term waxy barley is applied to cultivars that contain high levels of amylopectin, and nonwaxy barley is applied to barleys containing starch with the normal 3 : 1 ratio of amylopectin to amylose. The wax gene, located on chromosome 1(7H), conditions a high level (≈ 95%) of amylopectin starch and is recessive to the gene Wax , which is responsible for the 3 : 1 amylopectin/amylose ratio (Nilan 1964). Waxy barleys containing 100% amylopectin starch have been developed in conventional cross-breeding programs in Canada (Bhatty and Rossnagel 1997) and Sweden (Ajithkumar et al. 2005), and in Japan through chemical mutation using sodium azide (Ishikawa et al. 1995). Azhul, a waxy hulless barley, was the source of the waxy gene in the Canadian and Swedish reports. It is fairly well accepted that waxy barleys contain 5 to 8% less total starch than comparable nonwaxy types (Ullrich et al. 1986; Xue et al. 1997). However, the reduced level of starch is usually accompanied by small increases in the simple sugars fructose, glucose, and sucrose and the fiber component β-glucan (Xue et al. 1997).
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BARLEY FOR FOOD AND HEALTH Science,
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On a Seed “This was the goal of t
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Cover design by Jean Rose Johnston.
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CONTENTS Preface xiii 1 Barley Hist
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CONTENTS ix Infrared Processing, 12
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CONTENTS xi Asia, 221 Barley Mixed-
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xiv PREFACE In the concluding two c
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2 RELATIONSHIP OF HUMANS AND BARLEY
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Page 25 and 26: 8 RELATIONSHIP OF HUMANS AND BARLEY
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Page 35 and 36: 2 Barley: Taxonomy, Morphology, and
Page 37 and 38: 20 BARLEY: TAXONOMY, MORPHOLOGY, AN
Page 49 and 50: 3 Barley Biotechnology: Breeding an
Page 51 and 52: 34 BARLEY BIOTECHNOLOGY: BREEDING A
Page 73 and 74: 4 Barley: Genetics and Nutrient Com
Page 75: 58 BARLEY: GENETICS AND NUTRIENT CO
Page 79 and 80: 62 BARLEY: GENETICS AND NUTRIENT CO
Page 113 and 114: 96 BARLEY PROCESSING: METHODS AND P
Page 115 and 116: 98 BARLEY PROCESSING: METHODS AND P
Page 117 and 118: 100 BARLEY PROCESSING: METHODS AND
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110 BARLEY PROCESSING: METHODS AND
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134 EVALUATION OF FOOD PRODUCT QUAL
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7 Barley Food Product Research and
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146 BARLEY FOOD PRODUCT RESEARCH AN
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8 Health Benefits of Barley Foods I
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180 HEALTH BENEFITS OF BARLEY FOODS
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9 Current Status of Global Barley P
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206 CURRENT STATUS OF GLOBAL BARLEY
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208 CURRENT STATUS OF GLOBAL BARLEY
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10 Barley Foods: Selected Tradition
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212 BARLEY FOODS: SELECTED TRADITIO
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APPENDIX 1 Glossary: Botany and Pla
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APPENDIX 2 Glossary: Food and Nutri
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APPENDIX 3 Glossary: Barley Terms T
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APPENDIX 4 Equivalent Weights and M
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SOURCES OF BARLEY AND BARLEY PRODUC
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Rancho Cucamonga, CA 91730 Ph: 888-
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SOURCES OF BARLEY AND BARLEY PRODUC
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E-mail:Tony.Steeper@csiro.au Web: h
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BARLEY RESOURCE ORGANIZATIONS 241 P
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INDEX Air classification, 102, 122-
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INDEX 245 Meat and barley casserole
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