Comparison of the physicochemical properties of barley starches after partial α-amylolysis and acid/alcohol hydrolysis

Zero amylose waxy (CDC Alamo), normal (Falcon), and high amylose (CDC 92-55-06-48) hull-less barley starches were isolated and subjected to α-amylase (Bacillus licheniformis) hydrolysis (24 and 48 h; 50 and 500 U/g) and acid hydrolysis (2% HCl, 10 and 96 h) in different alcohol media (methanol, ethanol, and 1-butanol) to determine the molecular characteristics of the starch material remaining in the granules after treatments. The greatest yield of α-amylase-treated starches was obtained for the high amylose (79.9–86.6% w/w) followed by normal (61.1–76.1% w/w), and zero amylose waxy starch (44.2–64.5% w/w). Very little solubilization of starches occurred during acid/alcohol hydrolysis, and very high yields of treated starches were obtained (91–99%). Relatively small decreases in the average molecular weights (Mw) of starch components were observed after α-amylolysis; the extensive hydrolysis of the zero amylose starch (56% solubilization) caused only a threefold decrease in the Mw of amylopectin. The Mw of starch fractions after acid/alcohol hydrolysis was affected by the hydrolysis time and alcohol but not by the amount of amylose in the native starches; the Mw and the mode of distribution of various Mw species can be tailored to specific needs by choosing appropriate hydrolysis conditions. The partially enzyme-hydrolyzed normal and high amylose starches formed stronger gels (40% w/w) than their native counterparts, but waxy starch showed no evidence of network development during storage (20 h, 5 °C). The partially acid-hydrolyzed high amylose starch (2% HCl/MeOH, 10 h) showed significantly higher values of G′ compared to the native sample upon storage, whereas the partially hydrolyzed normal starch exhibited the G′ values similar to its native counterpart. Both normal and high amylose starches, hydrolyzed for 96 h, exhibited a rapid rise in G′ upon cooling but very little network development thereafter.