Preliminary Study On The Biosynthesis Of Main Active Ingredients Of Auricuralia Auricula

Auricuralia auricula is one of the common culinaiy and medicinal mushrooms,and melanin and polysaccharides are the important functional component of A.auricula. The active ingredients could extract from the fruiting-body of A. auricula.However, it is a long time to produce fruiting body of A. auricula. Submerged culture has become an effective method to produce active metabolites of microbe due to its high efficiency, controlled condition and suitability for industrialization. In this work,the strain mutagenesis, promoter screening, fermentation of soymilk by A. auricula,and melanin stability test were carried out and the results were as follows:(1) A good strain for melanin biosynthesis was obtained by the combination mutagenesis of U V and diethyl sulfate using the extracellular melanin as the index.The yield of melanin was 3.05 times compared with that of the original strain.(2) To improve the melanin and polysaccharide biosynthesis, the effects of exogenous substances such as fatty acids, vegetable oil, alcohol and Tween, Span,polyethylene glycol on the regulation of active ingredient biosynthesis by A. auricula were performed. The results showed that Tween 40,stearic acid, palmitic acid and oleic acid were beneficial to the biosynthesis of Auricularia polysaccharide, and the optimum addition amount was determined by orthogonal test as 0.5% of T,ween 40,1.5% of stearic acid, 0.1% of palmitic acid, 0.25% oleic acid, respectively. Methanol,span 20, polyethylene glycol 1000 could enhance the biosynthesis of melanin.Compared with the control, melanin production was respectively increased 2.5-fold,1.73-fold and 2.02-fold when 1% methanol, 1% span 20 0.25% polyethylene glycol 1000 was respectively added into the fermentation media.(3) Soymilk was fermented by A. auricula and the content of antioxidant activities and some ingredients such as polysaccharide, melanin, total phenolics and were measured during the fermentation. The results showed that the total reducing sugar, crude protein, free amino acid, raffinose and stachyose contents decreased; total phenolic content remained unchanged; polysaccharide firstly decreased and then increased; the content of total flavonoids increased; the activity of tyrosinase and glycosidase increased, and the content of genistin and daidzin decreased with the increase of genistein and daidzein. At the end of fermentation, the antioxidant activity of fermented soy milk was significantly improved.(4) The effects of physical and chemical factors such as pH, natural light,ultraviolet light, temperature, sugar, salt, citric acid, sodium benzoate and potassium sorbate on the stability of A. auricula melanin were studied. The results showed that the optimal pH for melanin solubility was 13; the stability of melanin was poor under natural light, but good under ultraviolet radiation; the stability of melanin was good with the addition of glucose and potassium sorbate, but poor with the addition of sodium benzoate and sodium chloride.