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Structural Changes of Starch Molecules in Barley Grains During Germination

¹Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China. ²University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia. ³University of Queensland, Centre for Plant Science, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia. ⁴Corresponding author. Phone: +61 7 3365 4809. Fax: +61 7 3365 1188. E-mail: b.gilbert@uq.edu.au

The germination of barley grains is an important step in malt production for beer brewing. This study examines the changes in starch molecular structure in barley grains under optimal conditions for sprouting. Two barley varieties were tested: Schooner and Grimmett, which are low and moderate dormancy grains, with >90 and <5% of grains germinating within two days in sprouting conditions, respectively. The barley grains were germinated in humid conditions after being soaked in excess water for 24 h. The grain weight and starch content of Schooner decreased significantly (P < 0.05) with germination time, whereas those of Grimmett showed no significant changes (P > 0.05). The starch chain-length distributions, analyzed from enzymatically debranched starch molecules with size-exclusion chromatography, indicated that the shorter amylopectin branches of Schooner were degraded at a faster rate than its longer amylopectin branches, which was also confirmed by the decreasing degree of branching with germination time. The changes in starch molecular structure of Grimmett grains were less apparent. The results of this study showed that barley grains containing shorter starch chains can produce sugars more quickly, which indicates that starch structure can serve as one of the specifications when selecting barley grains for brewing.