Extrusion Cooking of Grain Sorghum and Improvement of Its Qualities

Abstract

Grain sorghum (Sorghum bicolor (L.) Moench) is one of the most important crops in the world. It is not consumed as food, but used as feed especially in advanced countries. Its appearance, nutritional value and palatability should be improved for human consumption of the grains. For the purpose of such improvement, the extrusion tests of the grain sorghum were carried out here using a simple single-screw extruder. As a pretreatment of grain sorghum for extrusion, whitening by the abrasive milling machine to the yield of 70-80% was effective to improve expansion degree and decrease the polyphenol content. Good expansion was attained when the moisture content of the material was adjusted to 14%. The various high-protein ingredients were tested as additives in order to improve the nutritional value of the extruded products. Three ingredients, gluten-meal, defatted soyflour and dried yeast, were selected from the viewpoint of expansion degree. Among them, dried yeast was most attractive because it enriched most effectively extruded products with lysine and vitamin B₁. Much differences in expansion degree were found among the extruded products of the grain sorghum added with 10% of yeast cells commercially available in Japan, and brewer's yeast was found to be the most suitable. Addition of the brewer's yeast to the grain sorghum improved not only nutritional value but also expansion degree of the extruded product.