DISCOVERY OF GRAIN-SORGHUM GERM PLASM WITH HIGH UNCOOKED AND COOKED IN-VITRO PROTEIN DIGESTIBILITIES

Grain sorghum has been documented to have low protein digestibility re lative to other cereal grains. Low protein digestibility of sorghum is most pronounced in cooked foods and is ranked slightly lower than cor n as a feed grain. In this article, sorghum germ plasm is identified t hat has substantially higher uncooked and cooked flour in vitro protei n digestibility than normal cultivars. Sorghum lines were found within a high-lysine population derived from the mutant P721Q that have appr oximate to 10-15% higher uncooked and approximate to 25% higher cooked protein digestibilities using a pepsin assay. Highly digestible sorgh um grain showed little reduction in digestibility after cooking, compa red to the large reduction that is typical of normal sorghum cultivars . Using the three-enzyme pH-stat method, we showed that the highly dig estible lines had the same degree of peptide bond hydrolysis in approx imate to 5 min, as was found in 60 min in the normal cultivar, P721N. Differences in protein digestibility were related to enyzme susceptibi lity of the major storage prolamin, alpha-kafirin, that comprises appr oximate to 50-60% of the total sorghum grain protein. Using the enzyme -linked immunosorbent assay (ELISA) technique to track the pepsin dige stion of a-kafirin, the highly digestible lines had approximate to 90- 95% alpha-kafirin digested in 60 min compared to 45-60% for two normal cultivars. gamma-Kafirin, a minor structural prolamin found mainly at the periphery of protein bodies, was also somewhat more digestible in the highly digestible sorghums. Highly digestible grain was of a flou ry kernel type, though recently this trait has been found in a modifie d background. More digestible protein from sorghum grain, that additio nally is high in lysine content and has a fairly hard endosperm, could be of important benefit to populations who lack adequate protein in t heir diets, and may, pending further studies, prove to increase the va lue of sorghum as a feed grain.