2001

Lauro, Marianna

The susceptibility of native barley starch granules and granules at different stages of gelatinization to a-amylolysis was studied by analyzing the amounts of solubilizing carbohydrates. The subsequent changes in the structure and properties of the insoluble residue were analyzed by various methods. The early stages of a-amylolysis of gelatinized barley and waxy barley starches were also followed. The gelation behavior of enzymatic hydrolysates of waxy barley starch with different molecular sizes was studied. In the a-amylolysis of both gelatinized and ungelatinized barley starch, the molecular weights of both amylose and amylopectin decreased. Amylopectin hydrolysis started between the clusters without shortening of the external chains. In the early stages of a-amylolysis of barley starch granules, lipid-complexed amylose was less accessible and concentrated in the insoluble granule residue and the solubilizing carbohydrates originated from free amylose and amylopectin. Amorphous and crystalline regions of granules solubilized equally and with more extensive hydrolysis, the granular structure and crystallinity were destroyed. Partial gelatinization changed the a-amylolysis pattern and the pinholes typical of a-amylase-treated large barley starch granules could not be seen. With regard to the leaching of lipid-complexed amylose, the a-amylolysis was similar to that of native barley starch granules. Additional lipid binding to starch during partial gelatinization stabilized the granular structure. Along with lipid complexed amylose, the small amount of free amylose remaining also concentrated in the residue, indicating that free amylose no longer existed as separate molecules but rather as part of otherwise complexed and thus insoluble molecules. Partial a-amylolysis increased the solubility of barley starch and changed the mechanism of swelling of the granules; granules became more transparent and no twisting was observed.