Study On Submerged Culture Of Pleurotus Ostreatus And Its Application In The Field Of Flour Process

Currently, the quality of flour is very low in our country. It is very important to improve the the quality of flour with the advancement of people's living standard. The flour ameliorant used actual are chemically manufactured and will bring safety issue. So it is a key point to find a safe, cheap and easly gotten flour ameliorant. Enzyme such as xylanase and laccase are naturally and safely produced and being used as flour ameliorant. But how to produce it cheaply remains a question. With the development of biotechnology, the application of liquid fermentation on edible mushroom culture has progressively expanded.Nowadays, the study on its fermentation mainly focused on enzyme production and to produce large amount of bioactive substance such as protein, polysaccharide, vitamin, terpene and nucleic acid. Now, the technology of edible mushroom fermentation and the production of its nutriment and enzyme have successfully applied in the food, pharmaceautical industries. By virtue of its deep application in the flour manufacturing industry, the need for cheap culture technology should be explored extensively. Beer's spent grains, an offal of beer industry,which produce pollution issue but has mang nutrient, can be used as liquid culture medium for the edible mushroom.This paper studies the submerged fermentation condition of Pleurotus ostreatus to produce xylanase and laccase using beer's spent grains as main culture medium. This paper also reports the studies on the application of enzymes from edible mushroom in improving dough performance by the methods of dough farinograph and extensograph. The study included selection of the liquid medium, the optimum parameters of fermentation, the fermentation dynamics during fermentation and the enzyme property of xylanase and laccase. Finally, the experiment studied the effects of xylanase and laccase from Pleurotus ostreatus on dough characterization and bread making. The conclusion was as follows:(1) The optimum medium constitute of fungi fermentation in beer's spent grains by orthogonal test:Beer's spent grains 8g, soybean flour 0.16g, corn flour2g, sugar 2g;(2) The optimum liquid submerged culture condition was determined: 200ml liquid medium was added in 500ml shake flask; rotary speed was 160r/min, the culture temperature was 27℃, the best culture time was 3d. During this period, the content of reducing sugar was up to 0.980mg/ml at 24h, the amount of mycelia got highest of 27.92g/100ml at 72h, and the activity of xylanase and laccase were 13.3U/ml and 3.6U/ml respectively.(3) The enzyme characteristics about xylanase and laccase was determined:the best temperature of xylanase was 58℃, the optimum pH of xylanase was 5.0, and the value of Vmax and Km of xylanase were 11.48μg/(ml·min) and 7.74mg/ml respectively. The best temperature of laccase was 30℃, the optimum pH of laccase was 5.0; the Cu2+,Mn2+ Zn2+ had great effects on its activity at low concentration.(4) Based on its partial characterization of xylanase and laccase in the Pleurotus ostreatus ferment, the enzymes had great effect on the stability of dough and the enhancement effect on dough farinograph feasibility, it markedly improved the quality of baking and the baked bread, it also led to an increase in the volume and specific volume of bread. Additionally, its use led to a decrease in the hardness and springiness of crumb as well as significantly reducing retrogradation.(5) More over, the xylanase and laccase had different effects on the dough performance. The effect of removing dough water-holding characteristic by the xylanase was much greater than that of removing dough network structure by laccase, and the former was on dominant degree.(6) Conclusion, we had found a cheap way to produce enzyme such as xylanase and laccase to improve the quality of flour, by liquid fermentation of edible mushroom using beer's spent grains as main culture medium. The enzyme from fermented supernatant could be directly used to improve the dough performance. In this way, we not only found a cheaply way to improve the flour quality, but also opened a new to apply beer's spent grains. More over, it could also enhance the nutrition of flour by directly adding this enzyme containing fermented supernatant of edible mushroom. So that, the technology we developed had both the economic and social significance.