ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 66 Number 4
Improving the nutritive value of soyabean (Glycine max (L.) Merr.) through processing: biochemical and protein quality studies
The effects of different processing treatments on the proximate and mineral compositions, antinutritional factors and protein quality of six varieties of soyabean were investigated. The average crude protein value of the raw soyabeans was 38.1 % and the ether extract was 25.3%. Mineral concentrations on a dry weight basis were: 4.48-5.72 g kg-1 for P; 1.97-2.51 g kg-1 for Ca; 19.1-22.7 g kg-1 for K; 41.0-49.9 mg 100 g-1 for Na; 4.49-7.20 mg 100 g-1 for Fe and 13.8-16.9 mg 100 g-1 for Zn. In the processed beans, germinated, soaked-cooked and germinated-cooked samples showed considerable decreases in all nutrients, especially crude protein, P, K, Ca and Mg. Crude fibre increased in the germinated soyabeans and values obtained ranged from 2.61% in decorticated TGx 17-29E to 7.16% in germinated TGx 711-01D. Tannin expressed as tannin index, phytic acid and oxalates did not show varietal differences. Ranges of values obtained were 0.65-1.06 for tannins, 4.46-5.50 mg 100-1 for total oxalate and 0.32-0.44% for phytic acid. Decortication of soyabeans removed about 70% of the tannins. Germination and soaking were effective against phytic and oxalic acids and cooking losses were maximum for soaked-cooked and germinated-cooked soyabeans. The protein quality of the raw soyabean was significantly (P< 0.05) improved by processing. Gains in body weight of rats were negative for raw and germinated-cooked soyabeans but significantly (P< 0.05) improved in the other processed beans. Feed/gain ratio ranged 3.44-7.55 and PER was significantly (P< 0.05) highest in soaked-cooked soyabean and lowest in raw and germinated-cooked beans. PRE was improved from 28.0% for raw soya bean to 62.1 % after decortication, 55. 7% after autoclaving, and 64.5 and 68.2% after cooking the raw bean for 1 h and the soaked bean for 30 min, respectively. These differences were not reflected in protein digestibility, and digestibility values obtained did not show any significant differences between the raw and differently processed soyabeans.
Keywords: Soyabean; Raw; Processed; Nutrient composition; Antinutritional factors; Protein quality; Albino rat