Food chemical analysis of tempeh prepared from South African-grown soybeans

Abstract

Tempeh was prepared from locally grown soybeans of the cultivars Hutton and Prima, using the mould strain Rhizopus oligosporus NRRL 2549. The purpose of this food chemical study was to investigate the nutritionally beneficial changes which are brought about during fermentation, pending the probable introduction of the product to the South African market. Tempeh, fermented for 24, 48 and 72 h, together with unfermented controls and whole soybeans, were analysed for the proximate composition, phytic acid, specific carbohydrate materials including starch, mono- and oligosaccharides, minerals, thiamine, riboflavin and nicotinic acid; losses in dry mass occurring during fermentation were determined for tempeh made from Prima soybeans. Processing of soybeans into tempeh brought about favourable nutritional changes including reduction in the levels of phytic acid, starch and the flatulence-causing oligosaccharides stachyose and raffinose; whereas thiamine concentrations were reduced, riboflavin and nicotinic acid contents increased during fermentation. Brief comment is made on toxicological investigations concerning R. oligosporus. Tempeh was found to be an acceptable product that could be employed to promote greater utilisation of soybeans for human consumption in this country.