Effect of alkaline pretreatment and cooking on protein fractions of a high-tannin sorghum cultivar

A high-tannin sorghum cultivar (Karamaka) was used to study the effect of soaking in distilled water or 0.05%, 0.10% and 0.20% NaOH for 8 h, and soaking in distilled water or NaOH followed by cooking, on proximate composition, tannin content and protein fractions. Results showed that soaking the sorghum grains in water or NaOH for 8 h caused a slight increase in crude protein, whilst the tannin content significantly (p ⩽ 0.05) decreased. The highest drop in tannin content was observed after soaking sorghum in 0.20% NaOH for 8 h at ambient temperature. Combining soaking and cooking further lowered the tannin content of sorghum, with a maximum reduction of 83.9%. Soaking in NaOH and cooking caused significant (p ⩽ 0.05) increases in the albumin and globulin fractions, accompanied by a significant reduction in the glutelin fraction. This readjustment of sorghum protein fractions would indicate improvement in the quality of sorghum proteins.