Effects of Drying Methods on Physico-chemical Properties of Hydrocolloids Isolated from Peel Flour of Some Selected Root and Tuber Crops

Abstract

Hydrocolloids isolated from the flour of peels of selected root and tuber crops were purified and their physicochemical properties were determined using standard procedures. The experimental material used was the peels of three species of Dioscorea: alata (water yam), dumentorum (trifoliate yam), rotundata (white yam) and bulbifera (aerial yam); Colocasia esculenta (cocoyam); white and yellow flesh of Ipomoea batatas (sweet potato). The fresh peels were dried under three drying method (oven, sun and air-dried). Proximate composition gave 4.4 to 10.7% for moisture content, 0.40 to 6.10% for ash content, 0.32 to 4.13% for crude fibre and in carbohydrates it ranges from 81.3 to 93.7%. There were no fat and protein in the experimental samples. Oven-dried alata peel flour gave the highest swelling index value 1.44% while, air-dried had the highest value of (4.00%) ranking the highest in foaming capacities. The highest in water and oil absorption capacities were sun-dried (2.05) dumentorum peel and rotundata peel air-dried (2.21). In emulsifying capacity and freezing-thawing stability, the highest results were observed in colocasia peel oven-dried (54.3%) and white flesh Ipomoea batatas peel sun-dried (74.3%). Yellow flesh Ipomoea batatas (0.31 g/ml) gave the lowest in bulk density. Gelation temperature ranges from 70 to 83ºC with pH of 6.6 to 7.6.