Extraction of starch from sweet potato and its modification to cold water soluble by alkaline-alcoholic treatment

Abstract

Nigeria is among the largest world producers of sweet potato (Ipomoea batatas), but with all its potentials, sweet potato is only generally being consume as local food mostly in rural commununities. Famers encounter perennial problems with sweet potato because it is highly perishable; at post-harvest during storage and at pre-harvest on maturity, this causes huge economic burden. The goal of this work is to create ways of adding value to sweet poato produced in Nigeria. In this research, starch was extracted from sweet potato produced in Kano Nigeria, using wet milling method and filtration with 20μm 30μm and 40μm fabric filters obtaining dry weight percentage yield of starch to be 56.50%, 62.60% and 71.60% respectively, physico-chemical properties of all the isolated starch was found to match with standards sets for starch quality, yet starch extracted using 30μm filter exhibited better quality. The isolated starch was later subjected to modification into cold water soluble using alkaline-alcoholic treatment with different proportion of 3M NaOH and 40% aqueous ethanol lebelled P1, P2, P3, P4 and P5 each at three experimental temperatures of 25˚C, 30˚C and 35˚C. The results obtained showed that: at temperature of 25˚C P1, P2, P3, P4 and P5 treatments has percentage solubility in water as 43.30%, 47.20%, 55.50%, 66.10% and 81.40% respectively,at temperature of 30˚C P1, P2, P3, P4 and P5 treatments has percentage solubility in water as 46.10%, 50.80%, 56.90%, 65.70% and 85.00% respectively and at temperature of 35˚C P1, P2, P3, P4 and P5 treatments has percentage solubility in water as 50.10%, 55.40%, 63.20%, 74.20% and 90.30% respectively. Temperature and alkali equivalent demonstrate direct relationship with percentage cold water solubility of the potato starch with exeption of P4 at tempreture of 25˚C and 30˚C where it exhibited drop in solubility, while alcohol equivalent exhibits indirect relationship with percentage cold water solubility of the potato starch. The modified starches could be suitable raw material for different application in food and confectionary production, based on their percentage of cold water solubility.