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

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β-GLUCAN: THE CHALLENGE OF BARLEY AS FOOD 147 β-GLUCAN: THE CHALLENGE OF BARLEY AS FOOD If the primary purpose of adding barley to food products is to improve health benefits, the component in barley that is most valuable is β-glucan, either in its native form in the grain, concentrated in a milled fraction, or in an extracted purified product. Hence there is a dilemma in overcoming the characteristic physiochemical properties of β-glucan without destroying its beneficial attributes. A great amount of research has been reported on this topic in recent years, focusing on extractability, viscosity, molecular weight, and other physicochemical properties of β-glucan that affect food quality. Peter Wood of Agriculture and Agri-Food Canada has published reviews showing the relationships between solution properties and the physiological effects of β-glucan (Wood 2002; 2007). He concluded that because of the effects on β-glucan structure in processing, especially in reduced viscosity, which is crucial to physiological function, the amount of β-glucan alone cannot simply be related to the efficacy of a product. The wide range of effectiveness reported in various studies may be partially explained by the properties of β-glucan, especially viscosity. In this section we review some of the research studies reported on this subject. Robertson et al. (1996) investigated the susceptibility of barley β-glucan polymers to disruption during cooking and digestion. Their objective was to determine the effects of various methods of β-glucan extraction and to ascertain whether or not the product extracted maintained the character of soluble fiber capable of providing beneficial physiological effects in the intestine. They determined that enzymatic treatments were more effective than either chemical or physical methods on the extractability of β-glucan from the grain. During in vitro digestion of barley, proteolytic activity was noted, suggesting the existence of a proteoglycan complex in the barley endosperm cell wall. Knuckles and Chiu (1999) treated several barley varieties with heat and chemicals to determine the effects on β-glucanase activity and molecular weights of β-glucans. β-Glucanase activities were reduced by heating, alcohol treatment, and oven heating, while hydrochloric acid and trichloracetic acid treatments reduced extractability and molecular weights of β-glucans. These results are relevant for consideration in any barley food processing venture. Sourdough bread was made with two lactobacillus starter cultures using barley flour and two milled high-fiber barley fractions (Marklinder and Johansson (1995). The amount of β-glucans in the sour doughs decreased during fermentation to different degrees (18 to 31% versus 10 to 20%) with the two starter cultures, suggesting differences in the ability of the lactobacilli to degrade the polymers. Choosing the proper lactobacillus culture is therefore necessary to maintain levels of β-glucan in the end products. Izydorczyk et al. (2000) studied the effects of heat and physical and enzymatic treatments on total and soluble β-glucan content in flour from Canadian hulless barleys. Extractability of β-glucan from high-amylose barley was relatively low compared to normal, zero-amylose, and waxy barleys. Viscosity of barley flour slurries was affected by the proportion of soluble β-glucans, β-glucanase activity, and molecular weight of β-glucans. Hydrothermal treatments did not influence the
148 BARLEY FOOD PRODUCT RESEARCH AND DEVELOPMENT extractability of β-glucans, but did destroy β-glucanase activity, thereby preserving the molecular weight of β-glucans and maintaining viscosity. Izydorczyk and her group studied β-glucans and arabinoxylans by producing a pearling by-product (pearlings), fiber-rich fractions, and flour from three Canadian hulless barleys with normal, high, and low amylose content. The fiber-rich fraction contained the highest amount of β-glucans, followed by flour, and then the pearling by-product. The solubility of β-glucans was inversely proportional to the levels in the fractions. The pearlings contained the highest amount of arabinoxylans. There were structural variations in both β-glucans and arabinoxylans, derived from their localization within the kernel as well as barley variety. This study exemplifies the wisdom of choosing appropriate barley genotypes and combining processing and fractionation to achieve desired products for specific applications. More recently, Irakli et al. (2004) isolated water-extractable β-glucans from six Greek barley cultivars and measured structural features and rheological properties. There were wide differences in molecular weight and corresponding differences in flow behavior, shear thinning ability and gelling capacity among samples. In addition, various sugars added to the solutions varied in their effects on gelling. The rheological behavior of β-glucan solution flow properties and gelling properties were also investigated (Vaikousi et al. 2004; Vaikousi and Biliaderis 2005). Aqueous dispersions of β-glucans underwent morphological changes during freezing and thawing. Interactions with other components were reported, as well as differences between β-glucans of varying molecular weight. Another prolific research team, Charles Brennan and Louise Cleary of New Zealand and the United Kingdom, respectively, provided a comprehensive review of the use of β-glucan as a functional food ingredient (Brennan and Cleary 2005). This report summarized recent research and stressed the necessity for consideration of extraction procedures, molecular weight, and rheological characteristics of both extracted and native β-glucans in food. Symons and Brennan (2004a) evaluated extraction treatment on yield and composition of barley fractions, and the behavior of the fractions on starch gelatinization and pasting. Extraction with thermostable α-amylase yielded the purest β-glucan fraction. Inclusion of the fractions in starch–water dispersions significantly altered pasting characteristics related to viscosity. The effect was partially alleviated by substitution of 5% wheat starch with the fractions, which possibly reduced the enthalpy of starch gelatinization. In a complementary study, Symons and Brennan (2004b) extracted a β-glucan-rich fraction from Sunrise, a waxy hulled barley. The fraction, which contained 70% β-glucan, was incorporated into bread dough at 2.5 and 5%. Breads were evaluated for normal quality factors and also for reducing sugar release in a simulated digestion process. The rationale for measuring sugar release was to relate the soluble fiber content of the bread to a slower blood glucose response and hence a low glycemic index. The bread doughs with added β-glucan-rich fraction exhibited reduction in pasting characteristics and increased plasticity. The bread had reduced loaf volume and increased crumb firmness compared with control breads. Measurement of reducing sugars released over a period of 300 minutes was expressed in maltose equivalents as a percentage of
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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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10 RELATIONSHIP OF HUMANS AND BARLE
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2 Barley: Taxonomy, Morphology, and
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20 BARLEY: TAXONOMY, MORPHOLOGY, AN
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3 Barley Biotechnology: Breeding an
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34 BARLEY BIOTECHNOLOGY: BREEDING A
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4 Barley: Genetics and Nutrient Com
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58 BARLEY: GENETICS AND NUTRIENT CO
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Page 113 and 114: 96 BARLEY PROCESSING: METHODS AND P
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198 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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