Improved cassava starch granule stability in the presence of sulphur dioxide

Abstract

Sulphur dioxide addition, usually during the centrifugal or extraction stage of starch processing, is believed to improve starch extraction and is a common practice in Thailand. Examination of the effect of sulphur dioxide addition during commercial scale processing revealed that in addition to an obvious bleaching effect, inclusion levels, such that the final product contained 180 mg sulphur dioxide/g starch, also altered functional properties. Changes were thought to result from granule stabilization and to be acting at the level of amylopectin, this fraction was very much less stable to physical disruption when no sulphur dioxide was present. Increased granule stabilization was expressed by an increase in gelatinisation temperature of about 2 °C, a decrease in swelling at lower temperatures and paste viscosity. Entry and possibly exit of material into the granule was also influenced by the presence of sulphur dioxide - enzyme, acid and water were all apparently restricted in their access to the granule. In the presence of sulphur dioxide enzyme hydrolysis was both lower and of a pattern that indicated only surface activity, whereas granules that did not contain sulphur dioxide, enzyme activity occurred from within the granule, resulting in breakdown, fragmentation and increased hydrolysis (from 44.8 to 53.5%). Lower water absorption, granule swelling and limited acid hydrolysis all characterized starch samples containing sulphur dioxide. The influence of sulphur dioxide was thought to be at the level of granule structure and could not be accounted for by differences in proximate composition or microbial activity, both starch were identical in all respect except amount of associated sulphur dioxide.