Shumin Hu (1); (1) Tsingtao Brewery Co. Ltd., Qingdao, China
Malt and Grains
The main objective of this research was to investigate the effect of L-cysteine (L-Cys) as a food additive on malt quality during germination. Barley was laboratory-germinated from 0 to 5 days with different levels of L-Cys (0 mM, 2.5 mM, 5 mM, 10 mM). First, malts at days 2, 3, 4 and 5 of germination were obtained to determine the activities of alpha-amylase, beta-amylase, limit dextrinase (LD) and its inhibitor. The results showed that L-Cys addition increased the activities of total LD and decreased the activities of LD inhibitor at all germination times. Unlike total LD and LD inhibitor, activities of alpha-amylase, beta-amylase and free LD were increased with the addition of 2.5 and 5 mM L-Cys at germination days 1 to 4, whereas activities were decreased when higher L-Cys (10 mM) was added or germination time was longer (days 5). These results showed that L-Cys not only accelerated the synthesis and release of amylase, but also promoted protease activities, leading to the decrease of amylase with higher L-Cys addition or at longer germination time. Next, malts at germination day 4 with the addition of 5 mM L-Cys or not were mashed. As a result of higher amylase in malt with the addition of L-Cys during germination, the non-fermentable sugars were reduced, and the glucose and maltotriose were improved compared to the control. Furthermore, the effect of L-Cys on protein degradation was investigated. Low molecular weight protein increased and middle molecular weight protein decreased obviously in wort from the malt germinated with L-Cys, demonstrating that L-Cys promotes protein degradation by activating protease activities. Last, malt filterability with the addition of L-Cys was better than the control, maybe because L-Cys promotes the degradation of storage material (starch, protein and non-starch polysaccharide). In conclusion, L-Cys can react with the protein and regulate protein form by splitting the disulfide bonds, leading to better malt quality.
Shumin Hu, born in 1984, received a Ph.D. degree in fermentation engineering from Shandong University in Jinan, China. She joined in State Key Laboratory of Biological Fermentation Engineering of Beer, Co. Ltd. in August 2011 as a postdoctoral researcher. After finishing her postdoctoral career in 2014, she continues to work in Tsingtao Brewery Co. Ltd. and focus on the research of starch degradation, including amylase, malt quality evaluation and process control.