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During the mashing process for brewing beer, incomplete degradation of arabinoxylan in barley malt may cause an intense filterability problem. The present study cloned a putative arabinofuranosidase (AnAbf), one of the debranching enzymes, from Aspergillus niger, to explore its application for improving filterability. Recombinant AnAbf (rAnAbf) showed activity towards both synthetic and natural substrates, such as 4-nitrophenyl α- l -arabinofuranoside (pNPαAraf) and malt water extractable arabinoxylan (WEAX), which was maximized at a temperature of 50 °C and pH of 5.5. Metal ions did not increase the activity of rAnAbf, indicating a difference in its C-terminal domain from that of type II GH43 family members. rAnAbf also exhibited a synergistic effect with β-xylanase against WEAX. The filtration rate of the wort increased by 12.8% after supplementing with rAnAbf during the initial stage of mashing. A slight decrease in viscosity and an unexpected increase in turbidity were observed.

The effects of different dissolved oxygen concentrations (DOC) on the browning degree, amino acids, total phenols, reducing sugars, polyphenoloxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL) of pear wine, and the relationship between various quality indicators and browning degree were investigated. Dynamic model fitting analysis of the changes of physiochemical indicators of pear wine in the storage process were performed. The importance of the physiochemical indicators effect on the browning of pear wine during the storage process was analyzed by OPLS (orthogonal partial least squares discriminant analysis), and the effect of dissolved oxygen on the browning of pear wine was systematically revealed. The results showed that dissolved oxygen, total phenols and amino acids had the greatest influence on the browning degree of pear wine. It provided a theoretical basis for revealing the browning mechanism and inhibiting the browning of pear wine.

As a major component of non-starch polysaccharide in barley, arabinoxylan (AX) plays an important role in quality traits of malt and the final beer product. The Chinese barley malt has encountered filterability problems for a long time. The main reason caused by barley cultivar has been accepted in the malting and brewing industries. In our previous proteomic study, the peroxidase (POD) BP1 was found to be in quite high abundant in the filterability defect Chinese barley malt. Therefore, the present study tried to verify its negative effect on filterability, by surveying its activity in different malt samples and detecting effects of POD on AX gelation and filterability. The results showed that the activity of POD, as well as the content of AX bounded ferulic acid, were both negatively correlated with filterability, while the feruloyl esterase activity was positively correlated with it. In addition, AX gelation catalyzed by POD caused worse filterability, and the natural inhibitor of POD, vitamin C, could blocked the cross linking catalyzed by POD and thus improve the filterability. These results all suggested the great negative effect of POD on malt filterability.

Dan'er is a widely grown malt barley cultivar in China, but its filterability defects have severely impeded its application in beer brewing. Previous investigations have suggested that we should identify the malt filterability correlated proteins, one of which was postulated to be arabinoxylan arabinofuranohydrolase I (AXAH-I). To verify this hypothesis, we purified AXAH-I from Dan'er malt, characterised its enzyme performance, and investigated its influence on filterability by adding different amounts of purified enzyme to the mash. With 6 mU g(-1) malt AXAH-I supplemented, the wort separation rate increased by 31.8%, viscosity decreased by 3.6%, and the endosperm reserve contents declined concomitantly. Unexpectedly, the wort turbidity increased with increasing AXAH-I. We also tried to optimise the use of currently available commercial enzyme products for filterability improvement in beer brewing, by supplementing them with purified AXAH-I and β-amylase. AXAH-I could be a functional component for novel commercial enzyme products in the beer industry.

The variety of metabolic proteins theoretically reaches a peak at the end of germination in large-scale malting. In the present study, comparative proteomics based on two-dimensional fluorescent difference gel electrophoresis (2D-DIGE) was employed to quantitatively analyse the low-salt soluble proteins in green malts from cultivars of Dan'er and Metcalfe. Fifty-nine metabolic proteins with significant differences between cultivars were successfully identified using MALDI-TOF/TOF. The roles of differential proteins in malt quality discrimination were elucidated according to their functions. Among them, 18 proteins exhibited differences in the green malts but not in the malts between the two cultivars. They could be considered as supplementary contributors to the quality defects of Dan'er malt, and new markers for malt quality improvement.