Starch ester synthesis: effect of pH on the preparation of succinate corn starch

Ester synthesis of corn starch using octenyl succinyl anhydride was studied. The succinylation of starch (OSA starch) provides an opportunity to give the hydrophobic character to starch and regulate the physicochemical properties of this biopolymer. Thus this modification process widens applications of the starch in foods and non-food products. Effect of pH on the degree of substitution (ds) was studied. The experiment was conducted to test the joint effect of pH and the time of the reaction when the reaction temperature was held constant at 25°C. As the pH of the reaction medium increased from 7 to pH 8, the ds increased from 0.02 to 0.0238 and the ds decreased when pH was raised from 8 to pH 9. The highest level of ds (0.0238) was at pH 8. Considering the time of reaction, the results were discussed in terms of the nucleophilic substitution of hydroxyl group(s) of a starch molecule and the carbonyl group of the acid anhydride. Two of the physicochemical properties namely starch swelling and the starch paste clarity of the OSA starch were studied. Swelling as the index of the starch hydration, was 19.27 g/g for the OSA corn starch with ds of 0.0238. Paste clarity as an indication of the state of starch dispersion and the retrogradation tendency was also measured (% light transmittance at 650 nm). Result of paste clarity for the OSA corn starch was 9.61 when the ds value was 0.0238 at pH 8. Importance of use of the OSA starch as encapsulate of the food flavorant in the preparation of oil- in- water (O/W) emulsion is mentioned.

Keywords:

OSA corn starch , paste clarity , swelling power , succinylation , starch ester synthesis