The effect of fermentation, malt pre-treatment and cooking on anti-nutritional factors, in vitro protein digestibility, protein fractions and Thiol content of two sorghum(Sorghum bicolor L. Moench

Sorghum plays a significant role in the food security of the rural populations of Southern and Eastern Africa. Unfortunately, sorghum has low nutritional value and inferior organoleptic qualities. In addition, sorghum proteins are believed to be less digestible than those of other cereals. However, fermentation and germination has been cited as good options for increasing digestibility and improving nutritional quality of sorghum. In our study two sorghum cultivars Mugud (low in tannin) and Karamaka (high in tannin) were used. Investigation showed that the two cultivars contained: 7.7, 6.1% moisture, 3.6, 3.5% fat, 1.6, 1.4% ash, 2.6, 2.3% crude fibre, 10.2, 10.7% crude protein, 74.4, 76.1% carbohydrate 0.60, 3.02% (Catechin equivalent) tannin and 236.0, 280mg/100g phytate for Mugud and Karamaka, respectively. In vitro pepsin digestibility was 12.1 and 11.7% for Mugud and Karamaka, respectively. The protein fractions of untreated flour showed that the two cultivars contained: 15.05, 14.82% Globulin + Albumin, 22.2, 22.8% kafirin, 31.06, 30.70% G1-Glutelin, 5.85, 6.85% G2-Glutelin, 23.7, 22.72 G3-Glutelin and 1.7, 2.4% insoluble protein for Mugud and Karamaka, respectively. Fermentation significantly (P X04; 0.05) reduced the phytate (by 70.2%) tannin (by 67.3%) for two cultivars. Fermentation led to a decrease in thiol content. In contrast, fermentation increased in vitro protein digestibility. Fermentation also increased the level of Albumin + globulin fractions and the kafirin fraction and only slightly the total protein content for both cultivars. Fermentation with 5% malt addition showed a significant (P < 0.05) reduction in anti-nutritional factors: 78.3 and 85.3% reduction in phytate content and 78.3, 71.2% reduction in tannin content for Mugud and Karamaka, respectively. A significant (P < 0.05) increase in total protein occurred in the presence of malt compared to fermentation alone. Also the Albumin + Globulin fraction was significantly (P < 0.05) enhanced as well as the in vitro protein digestibility compared to fermentation alone. Cooking slightly reduced phytic acid for untreated sorghum dough by about 8.0% for both cultivars. Cooking of fermented product at the end of fermentation reduced phytic acid content by 9.6 and 11.0% for fermented product and 13.4, 13.8% for malted and fermented product for Mugud and Karamaka, respectively. Cooking significantly (P < 0.05) reduced Albumin + Globulin fraction but the reduction was lower in malted cooked samples. A highly significant increase in G3-Glutelin occurred in fermented cooked samples compared to fermented samples in the presence of 5% malt.
malt pre, sorghum
University of khartoum