Improvement Of The Baking Quality By The Psychrophilic Xylanase

With the development of the living standard of the people and the development of food industry, people have paid more attention on the quality and safety of the wheat flour and on the food made with wheat flour recently. Enzyme preparations, which deactivated during baking in most cases, are harmless for human body. Recently, the study of developing new enzyme preparations instead of chemical additives and researching the enzyme mechanism has been has been a hot research field in the world.Xylanases are widely used as flour modifier in food industry. Many researches had shown that the dough with adequate xylanases had batter springiness and shorter development time, loaf volume, crumb structure and loaf flavour were all improved. Moreover, xylanases also can make the shelf life of the loaf much longer. The action of xylanase on dough and bread varies because of the variety of pentosans in different wheat types and the variety of specificity of xylanases toward different substrates.Although a lot of xylanases have improvement on breadmaking and are even widely used in baking industry, only one GH 10 xylanase has been reported to be effective in baking. In this study, two GH 10 xylanases, cold-adapted Xyn A and mesophilic EX1, were compared for their effectiveness in breadmaking. The Xyn A was purified from Glaciecola mesophila KMM 241 bought from DSMZ with the culture collection number 15026T and its purification was accomplished with Guo Bing. As for the EX1, it was acquired from Trichoderma pseudokoningii K9301 preserved in our laboratory, whose purification was finished with Chen Leilei.In the paper, the optimum dosage of the two xylanases was analyzed with different concentration gradients respectively. According to the research, the optimum dosage of the two enzymes to improve the quality of wheat flour dough and bread was 270 U/kg flour for EX1 and 0.9 U/kg flour for Xyn A, showing that the dosage of cold-adapted xylanase was much smaller. Xyn A has an optimum temperature of 30°C and retains 23% and 60% activity at 4°C and 20°C, respectively. The inherent high activity of the cold-adapted enzyme at the temperatures used for dough preparation and proofing may be one of the determinative factors in its observed high efficiency. This characteristic may lead to the rather small dosage of cold-adapted xylanase used in breadmaking. That's one of its potential as additives in baking.With the optimum dosage, Xyn A and EX1 had the same dough-softening ability, 50% reduce in BU. However, Xyn A was more effective in reducing DDT than EX1.Xyn A and EX1 showed similar effect on improvement of bread volume (around 30% increase), whereas EX1 was more effective in reducing the initial crumb hardness. The cold-adapted xylanases have much lower thermostability than mesophilic homologues. Xyn A loses more than 95% of its activity when incubation at 40°C for 10 min, whereas EX1 keeps stable at 40°C for 50 h . Therefore, it can be predicted that, while Xyn A quickly losses its activity in the proof process, EX1 still further hydrolyzes the xylan in dough during proofing, which may be the main reason for the more effectiveness of EX1 in reducing the initial crumb hardness than Xyn A.Although they exhibited similar anti-staling effect on bread based on decrease in bread hardness, Xyn A showed more affect on reducing firming rate, and EX1 more on reducing initial crumb hardness. This difference may be related to their mode on xylan. Xyn A is a strict endo-enzyme with no xylose in its xylan-hydrolyzing product (Guo et al, 2009). EX1 is an endo-enzyme with some exo-enzyme activity and therefore there is some xylose in its xylan-hydrolyzing product.These results showed that the two GH 10 xylanases have respective advantages in improving the quality of dough and bread, and suggested their potential as additives in breadmaking.