Physicochemical properties and structure of large, medium and small granule starches in fractions of normal barley endosperm

Normal barley grain was milled to flour with a machine used to polish brewe rs' rice from the surface layer to the center. Large (18.4 mum, median size ), medium (12.3 mum) and small (2.2 mum) granule starches were isolated fro m classified flours. Their physicochemical properties and fine structure we re investigated. The percentage (w%) of large granules decreased from the s urface layer to the center, while the amounts of medium and small granules increased. Although all the starch granules were an A-type crystal, the rel ative crystallinity varied from 22.0 to 27.4%. The DPn of the amyloses was around 1600 and similar for all the samples. But the amylose content of the starches varied from 21.9 to 26.4%. Rise, the amylopectins showed differen ces in DPn (around 5700-7900) and chain-length distribution between granule size or fractions. The transition temperature ranges and the enthalpy valu es of the starch granules differed with granule size. The gelatinization pr operties showed no correlation with any of the parameters, except the entha lpy value and relative crystallinity (gamma = + 0.73). The findings suggest ed that the structural characteristics of the starches in classified flours of normal barley differed essentially from those of waxy barley. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.