Effect of extrusion processing on the nutritional value and tannin content of sorghum – soybean composite supplementary product

The study was designed to formulate sorghum-soybean composite supplementary foods and investigate the effect of extrusion on nutritional value and tannin content. The products were extruded and analysed for nutritional value, tannin content, urease activity, sensory and anti-oxidant activity. Results showed that, the extruded composite products had good nutritional value and conformed to the requirements for supplementary foods for older infants and young children. Nutritional composition of the composite supplementary foods were: protein 17.36 – 21.60 g/100 g DM, carbohydrates 67.35 – 77.46 g/100 g DM, fat 1.85 – 8.27 g/100 g DM, energy values 400.91 – 424.06 Kcal/100g and had appreciable quantities of Ca (77.57 – 272.37 mg/100 g DM), Zn (1.61 – 3.15 mg/100 g DM), Fe (2.72 – 11.21 mg/100 g DM), Mg (53.46 – 132.78 mg/100 g DM), Cu (0.51 – 0.83 mg/100 g DM) and K (74.14 – 255.61 mg/100 g DM). Extruded composite products had good physical and sensory attributes. A test of antioxidant activity using DPPH (1,1- Diphenyl- 2-picryhydrazyl) demonstrated considerable radical scavenging activity for all the products (71.79 – 97.91 μg/ml). The highest radical scavenging effect was observed in plain red sorghum (RS-C) with EC 50 value of 68.32 μg/ml. Extrusion resulted in loss of antioxidant activity by 1 – 20%. Extruded products had significantly lower concentrations of tannin and urease activity compared to the non-extruded products. The extruded products had higher WAI, WSI and were more acceptable than products that were not extruded. Based on the results, it may be concluded that, various blends of sorghum with sardines and soybeans can be used to produce high quality supplementary foods. Extrusion adds value to the products in that it transforms the products into instant, convenient products with better organoleptic properties. Therefore, extrusion technology should be adopted by small and medium scale food processors.

Tanzania Bureau of Standards (TBS)