Physico-chemical Properties of Starches from Two Varieties of Sweet Potato and Yam Tubers Available in Nigeria

Abstract

The research sought to investigate the functional properties of starches obtained from four Nigerian root and tubers, yam and sweet potato varieties, in order to facilitate their exploitation as substitute raw material for the local food and pharmaceutical manufacturing industry. The varieties, namely: white yam (Dioscorea rotundata), water yam (Dioscorea alorta), orange flesh sweet potato (Ipomoea batatas) and cream flesh sweet potato (Ipomoea batatas), their respective starches were obtained by wet separation techniques and were analyzed for their pasting properties, physic-chemical properties, starch yield on dry and wet basis, functional, starch purity, amylase and amylo-pectin were undertaken in order to determine their suitability for food and other uses. The peak time, pasting temperature, peak viscosity, holding strength, breakdown, set from peak and set back from through ranged from 7.3 – 8.3 mins, 65.4 – 71.3°C, 511.5 – 1001.2 BU, 860.8 – 871.3 BU, 300.1 – 306.9 BU, 240.8 – 248.1 BU and 400.4 – 510.9 BU respectively. There were significant differences (p<0.05) in the pasting properties. The crude protein, crude fat, crude fibre, ash, moisture and carbohydrate ranged from 1.55 – 1.85%, 0.09 – 0.12%, 0.12 – 0.22%, 1.32 – 2.05%, 10.72 – 11.09% and 85.59 – 86.20% respectively. There were significant differences (p<0.05) in the proximate composition of the starches. The starch yield on dry weight basis, starch weight on fresh weight basis, starch yield from tubers and percentage dry matter ranged from 56.84 – 85.88%, 22.75 – 36.07%, 18.02 – 26.00% and 40.02 – 44.01% respectively. There were significant differences (p<0.05) in the all the parameters. The bulk density, water absorption capacity, oil absorption capacity, gelatinization temperature, starch purity, amylase, amylo-pectin and pH ranged from 0.56 – 0.61g/cm3, 86.8 – 99.4%, 103.2 – 125.4%, 59.78 – 60.42°C, 95.28 – 96.55%, 27.25 – 29.37%, 70.63 – 72.63% and 6.82 – 6.91 respectively. There were significant differences (p<0.05) in all the parameters but no significant difference (p>0.05) in the pH. The starches from yam and sweet potato varieties starches can be exploited for diverse uses based on their different characteristics.