Effects of L-ascorbic acid on the conversion of cassava starch

Studies have previously shown that the inclusion of ascorbic acid with starches, which are then gelatinised in excess water, causes differences in the amount of starch conversion. Also, incorporation of ascorbic acid in dilute pastes has been shown to decrease the viscosity of the paste when stored at a range of temperatures. In this study the pasting behaviour of cassava starch in the presence of ascorbic acid has been followed using a Rapid Visco Analyser. Decreases in peak and final viscosity were apparent, with the largest reductions being with the highest amounts of ascorbic acid addition (0.1%). In contrast with other published work the effects of ascorbic acid on heating pastes made with a high starch content were studied. The amount of conversion of cassava starch was estimated by assessing the volume occupied by the swollen granules and the amount of soluble material released. Viscosity measurements of the starch polysaccharides after solubilisation in alkali were also established. Pasting behaviour of the samples that had previously been heated in the presence of ascorbic acid and buffer was also assessed. Ascorbic acid inclusion seemed to affect starch conversion with the results for peak and final viscosity correlating with the alkaline viscosity estimates. The inclusion of ascorbic acid also alters the appearances of the starch sample. Ascorbic acid inclusion made the samples lighter in colour and they did not hold their shape after processing. (C) 1999 Elsevier Science Ltd. All rights reserved.