Swelling and Enzymatic Hydrolysis of Starch in Low Water Systems

The matrix effects of starch to water ratio, temperature and time on the gelatinisation, swelling and enzymatic (alpha -amylase) hydrolysis of five starches (waxy maize, maize, wheat, tapioca and potato) were investigated. It was established that by controlling the extent of gelatinisation with appropriate incubation conditions, some residual order could be retained. With starch to water ratios of 1:1, the amount of residual order represented 67·5, 40·9, 37·7, 30·3 and 15·1 for waxy maize, maize, wheat, tapioca and potato starches respectively. Whilst gelatinisation was controlled by the availability of water together with temperature and time, the effect on swelling was more marked. This reflects the fact that although granule order may be (just) lost under limiting (water) conditions, the expansion of amorphous material is more extensively moderated when water is restricted. Under the conditions investigated, the amount of hydrolysis exceeded the swelling factor which shows that although the granules may be only partially swollen, they are susceptible to amylase hydrolysis and hence potentially digestion. However, the amount of hydrolysis is also intimately related to the extent of gelatinisation which has important implications to food, alcohol production and other industrial processes.