The structure of barley endosperm - An important determinant of malt modification

Structural differences in barley grains have been classified as either meal y or steely and their relative proportions have been determined using a lig ht transflectance method in three barley samples varying in the degree of s teeliness, Target being the most steely and Chariot most mealy with Blenhei m being intermediate. These structural differences were found to be associa ted with differences in the concentration of endosperm components, particul arly proteins and beta-glucan. Analysis of nitrogen within the endosperm sh owed that protein was mainly concentrated in the embryo and distal regions with the inner, mid-endosperm containing lowest levels. As the total nitrog en (TN) of the grain increased, the mealier samples accumulated nitrogen ma inly in the embryo whereas the steely sample had higher levels in the centr al endosperm. SDS-PAGE showed no differences in the protein banding pattern at different TN levels. Electron microscopy using immuno-gold labelling de monstrated that gamma-hordeins were present in sub-aleurone and outer endos perm whereas the C-hordeins were found throughout the central endosperm. Ho wever, steely areas of central endosperm contained gamma-hordeins. During m alting, protein modification in Chariot was more extensive than in Target w ith 34kD and 97kD hordeins being completely degraded. In Chariot and Blenhe im, level of beta-glucan was low and it was evenly distributed throughout t he endosperm. In the steelier Target, however, the amount of beta-glucan wa s higher and was concentrated in the proximal. and distal areas of the endo sperm. Steely grains (containing high concentrations of protein and beta-gl ucan) displayed slower water distribution during steeping and later develop ment and distribution of beta-glucanase during germination. As a consequenc e, the steely sample achieved a lower degree of modification during malting . The structure of the endosperm, therefore, has a prime influence on the e venness of distribution of moisture and enzymes which is crucial for homoge neous modification during malting. (C) 1999 Society of Chemical Industry.