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

Abstract

Normal barley grain was milled to flour with a machine used to polish brewers’ rice from the surface layer to the center. Large (18.4 μm, median size), medium (12.3 μm) and small (2.2 μm) granule starches were isolated from classified flours. Their physicochemical properties and fine structure were investigated. The percentage (w%) of large granules decreased from the surface layer to the center, while the amounts of medium and small granules increased. Although all the starch granules were an A-type crystal, the relative crystallinity varied from 22.0 to 27.4%. The DP n 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%. Also, the amylopectins showed differences in DP n (around 5700–7900) and chain-length distribution between granule size or fractions. The transition temperature ranges and the enthalpy values of the starch granules differed with granule size. The gelatinization properties showed no correlation with any of the parameters, except the enthalpy value and relative crystallinity ( γ=+0.73). The findings suggested that the structural characteristics of the starches in classified flours of normal barley differed essentially from those of waxy barley.