Nutritional evaluation of sorghum as affected by germination with main reference to dietary bulk and protein quality

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Date

1984

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Sokoine University of Agriculture

Abstract

The nutritional value of sorghum as affected by germination and different dehulling techniques was studied with emphasis on protein quality, dietary bulk and food intake. Two low-tannin and two high-tannin varieties were investigated. Nutrient content was affected by germination: minor changes occurred in proximate composition, except for a significant decrease in oil in all varieties. Thiamine, riboflavin and niacin content increased. Lysine increased in all varieties and the other essential amino acids in­ creased marginally. Dietary fibre was unaffected. Tannin content decreased significantly. Traditional and abrasive dehulling decreased the amount of protein, oil, dietary fibre, minerals, tannins and phytic-phosphorous. protein digestibility was Nutrient availability measured in vitro: significantly higher in the low-tannin varieties. Germination and dehulling increased digestibility in all varieties. Cooking reduced protein digestibility in the high-tannin varieties and significantly more than in the low-tannin cultivars. Iron availability was low in all varieties and increased only in one high-tannin variety after germination. Nutrient availability measured in vivo by rat-bio-assay: protein digestibility was high in low-tannin cultivars but low in high-tannin varieties. Germination increased digestibility only in one high-tannin variety. Biological values were higher in the high-tannin varieties. BV and NPU were not affected by germination. In vivo iron availability was higher in the low-tannin varieties and was increased by germination in only one of the high-tannin varieties. Zinc availability was low and was unaffected by germination and tannin content. Dietary bulk and food intake: When preparing weaning gruels, three times as much germinated flour of the low-tannin varieties, as compared to ungerminated, could be mixed into the same volume, while maintaining the same consistency of the gruel. Germinated flour of high-tannin varieties did not have this effect. Addition of 5% germinated low-tannin sorghum flour (enzyme-rich) to thick ungerminated gruels reduced the viscosity to acceptable weaning food consistency. This method of reducing dietary bulk of weaning food was accepted and used by mothers at village level. Food intake by 12-48 months old preschool children was significantly higher for bulk-reduced low viscosity gruel with 20% solids, compared to untreated gruel. It was concluded that sorghum nutrient content is comparable to other cereals except for the high tannin content. Germination generally improves nutritional value through increased lysine, better protein digestibility and reduction of anti nutritional factors, mainly tannins. The use of bulk-reduced high nutrient density weaning foods could eventually improve the nutritional status of young children.

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Keywords

Sorghum-germination, Milling, Nutrient content and availability, Dietary bulk, Weaning food intake

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