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Effect of Partial Gelatinization and Lipid Addition on α-Amylolysis of Barley Starch Granules

¹VTT Biotechnology, P.O. Box 1500, FIN-02044, Finland. ²Corresponding author: Phone: +358 9 456 6178. Fax: +358 9 455 2103. E-mail: Marianna.Lauro@vtt.fi

The effect of partial gelatinization with and without lipid addition on the granular structure and on α-amylolysis of large barley starch granules was studied. The extent of hydrolysis was monitored by measuring the amount of soluble carbohydrates and the amount of total and free amylose and lipids in the insoluble residue. Similarly to the α-amylolysis of native large barley starch granules, lipid-complexed amylose (LAM) appeared to be more resistant than free amylose and amylopectin. Partial gelatinization changed the hydrolysis pattern of large barley starch granules; the pinholes typical of α-amylase-treated large barley starch granules could not be seen. Lipid addition during partial gelatinization decreased the formation of soluble carbohydrates during α-amylolysis. Also free amylose remained in the granule residues and mostly amylopectin hydrolyzed into soluble carbohydrates. These findings indicate that lysophospholipid (LPL) complexation with amylose occurred either during pretreatment or after hydrolysis, and free amylose was now part of otherwise complexed molecules instead of being separate molecules. Partial gelatinization caused the granules to swell somewhat less during heating 2% starch-water suspensions up to 90°C, and lipid addition prevented the swelling completely. α-Amylolysis changed the microstructure of heated suspensions. No typical twisting of the granules was seen, although the extent of swelling appeared to be similar to the reference starch. The granules with added LPL were partly fragmented after hydrolysis.