Swelling and enzymatic hydrolysis of starch in low water systems

The matrix effects of starch to water ratio, temperature and time on the ge latinisation, swelling and enzymatic (alpha-amylase) hydrolysis of five sta rches (waxy maize, maize, wheat, tapioca and potato) were investigated. It was established that by controlling the extent of gelatinisation with appro priate incubation conditions, some residual order could be retained. With s tarch 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 a vailability of water together with temperature and time, the effect on swel ling was more marked. This reflects the fact that although granule order ma y be (just) lost under limiting (water) conditions, the expansion of amorph ous 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 swolle n, they are susceptible to amylase hydrolysis and hence potentially digesti on. However, the amount of hydrolysis is also intimately related to the ext ent of gelatinisation which has important implications to food, alcohol pro duction and other industrial processes. (C) 2001 Academic Press.