Effect of reaction temperature and sodium tripolyphosphate (STPP)/ starch ratio on phosphorylation of sweet potato (Ipomoea batatas L.) starch

Abstract

Sweet potato (Ipomoea batatas L.) is an important tropical root crop originated from Central America. Sweet potato starch (SPS) has good free swelling and non-congealing properties suitable for industrial food applications, particularly when it is used as thickener or water retention agent. Sweet potato starch has been traditionally used in China, Taiwan, and Korea, and is considered as emerging commercially potential starch in South East Asia. In this research, modified SPS was synthesized using sodium tripolyphosphate (STPP) as reagent. Phosphorylation was performed at temperatures of 110-140 oC using intakes of 2.5%-7.5%-weight of STPP (based on dry starch). The experimental result shows that Degree of Substitution (DS) of the products is accessible in the range of 0.0026-0.0103. Modified starch products have significantly higher swelling power (7.337-11.108 g/ g) and solubility (2.757-6.302 %-w/ w) compared to native SPS (swelling power = 7.358 g/g and solubility = 2.329 %-w/w). Phosphorylation also significantly improved paste clarity of SPS to 15.4-45.3 %-T (compared to 15.3 %-T for native SPS). The result suggests that phosphorylation is a promising method for SPS modification.