Effect of Heat Moisture Treatment Conditions on Swelling Power and Water Soluble Index of Different Cultivars of Sweet Potato (Ipomea batatas (L). Lam) Starch

A study was done to analyse the change in swelling power (SP) and the water soluble index (WSI) of native starches obtained from five different cultivars of sweet potatoes (swp 1 (Wariyapola red), swp 3 (Wariyapola white), swp 4 (Pallepola variety), swp 5 (Malaysian variety), and swp 7 (CARI 273)) commonly consumed in Sri Lanka. Extracted starch from fresh roots, two to three days after harvesting has been modified using 20%, 25%, and 30% moisture levels and heated at 85°C and 120°C for 6 hours and determined the SP and WSI. Results were subjected to general linear model, and analysis of variance (ANOVA) was carried out by using MINITAB version 14. Overall results showed a significantly high level ( ) of SP and WSI in all the cultivars of moisture—temperature treated starches than their native starch. Correlation analysis showed an effect on SP with the variation in the cultivar, temperature, and moisture; temperature combination and moisture alone had no significant effect. Significantly high levels of swelling power ( ) were observed in 20%—85°C, and 30%—120°C and the highest amount of swelling in the modified starch than its native form was observed in swp 7 cultivar. Results revealed a nonlinear relationship in the WSI with the cultivar type, moisture level, and the lower moisture—temperature combinations but higher temperature—moisture combinations had a significant effect. SP and WSI had a slight positive linear relationship according to analysis. Based on the results, a significantly high level of swelling and water solubility of native starches of different cultivars of sweet potatoes can be achieved by changing the moisture content to 30% and heating at 120°C for 6 hours. 1. Introduction For a wide range of starch applications, native starches cannot be used due to inability to bring out the desired properties. Native starches can be modified to obtain the desired qualities by starch modification methods. Chemical modification of starch molecules is commonly used in achieving the desired properties. Also by using specific moisture and temperature conditions, some physicochemical properties of starch can be altered. There are more trends in the world for physical modification of starch which is used in food industrial applications as there is an increasing difficulty in obtaining regulatory approval of the new chemical reagents and higher levels of treatment as described by BeMiller [1]. Since most physical modifications involve only water and heat, these hydrothermal treatments are considered to be natural and safe materials by Jacobs and