Effects of lipids, heating and enzymatic treatment on starches

The effects of heat treatment on oat and barley starch water dispersions were investigated. As compared with barley starch, the granules from oat starch were more degraded, but the fractionation patterns of both starches were not significantly different. Microscopic examination indicated that no evidence of amylopectin fragments was observed in the liquid fraction after starch dispersions were treated at 95°C even though chemical analysis demonstrated the solubility of both starch polymers. True solubility of oat starch was lower than that of barley starch, but the difference disappeared after removing the lipids from oat starch. By applying sequential centrifugation for starch dispersions, treated above 90°C, a fraction rich in an amylose-lipid complex could be produced. Studies on crystallisation of starch gels were performed. The crystallisation rate of a gel prepared from oat starch was lower than those prepared from other cereal starches (barley and wheat). The effects of polar lipids separated from oats (oat lecithin) on crystallisation of wheat starch gel were investigated and compared with soya lecithin. Furthermore, the behaviour of polar lipids in the starch gel was compared with their effect on bread staling. Even though oat lecithin hydrolysate affected the crystallisation rate positively, soya lecithin hydrolysate was more effective both in gel as well as in bread. The ability of esterases to hydrolyse lipids of barley starch at temperatures close to gelatinisation and of the gelatinised barley starch was examined. The extent of lipid hydrolysis of starch granules was only about 20%, but almost all of the lipids of the gelatinised starch were hydrolysed at 40°C. The effect of freezedrying on α-amylolysis of potato starch was also investigated, and was observed to greatly enhance the enzyme accessibility of the granules.