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

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