Comparative studies on the components of cereal grain that are undigestible in vitro

Abstract

The protein contents of the combined enzyme-extractable and enzyme- unextractable fractions in the procedure of Asp et al . ( J. Agric. Food Chem. 31 (1983) 476-482) ranged from 17% in wheat to 27% in barley; 20-25% of the undigestible protein was found in the extractable fraction. The interspecies variability in the cereal grain components that were undigestible in vitro was due primarily to the enzyme-extractable fraction. The differences involved: (i) the amounts of saccharides solubilized during the digestion procedure (from 27 mg/g grain meal in wheat to 38 mg/g in rye); (ii) the saccharide/protein ratios (ranging from 7 in rye and triticale to 5 in wheat and barley); and (iii) the compositions of both polysaccharides and protein. Arabinose and xylose in the rye enzyme-extractable fraction comprised 80 of the total undigested polysaccharide, and for wheat and barley these values were 55% and 30%, respectively. The content of protein-bound basic amino acids in this fraction was also higher in rye than in other cereals. Variation was less among the enzyme-unextractable fractions. It appears that the content and composition of the enzyme-extractable fraction may influence the nutritive value of cereal grain significantly. Carbohydrate-protein conjugates in this fraction may also have an important effect.