Medium Optimization Of ?-polyglutamic Acid Produced By Bacillus Amyloliquefaciens Fmbj37 And Application

y-polyglutamic acid is a new type of environmentally friendly biopolymer material,which formed by dehydration condensation of L-glutamic acid and D-glutamic acid.Substance and molecular weight of y-polyglutamic acid distributed from 10,000 to 2 million.It has good water solubility,metal ion adsorption,biodegradability and harmless.Therefore,it is widely used in food,cosmetics,medicine,health care products and environment protection,such as food thickening,texture improvement,cosmetics moisturizing,drug deliver carrier,heavy metal chelation absorption,agriculture,forestry and water conservation.At present,the production of y-polyglutamic acid is through microbial fermentation.However,the low fermentation yield and high production cost of?-polyglutamic acid restricts the industrial application.Therefore,we uses the response surface method to optimize the fermentation medium of y-polyglutamic acid to improve its yield.Besides,the application of ?-polyglutamic acid in freeze-drying protection and peach Xiahui No.8 preservation was studied.The main results are as follows:1.Optimized the medium of y-polyglutamic acid produced by Bacillus amyloliquefaciens fmbj37The strain of Bacillus amyloliquefaciens fmbj37 was selected and its composition of y-polyglutamic acid fermentation medium was optimized by response surface methodology.First,through the single factor experiment,determine the best carbon source,nitrogen source and its concentration,and the concentration of sodium glutamate,dipotassium hydrogen phosphate,magnesium sulfate,potassium chloride,ferrous sulfate,manganese sulfate and copper sulfate.Subsequently,the importance of these nine factors was examined by Plackett-Burman.The results showed that sucrose,sodium glutamate and dipotassium hydrogen phosphate were the main factors affecting the yield of y-PGA,and then the steepest climbing of these three factors was carried out.Then the steepest climbing experiment was carried out on these three factors,and the concentration range of the concentration was determined.Finally,the Box-Behnken design was used to find that the optimal addition amount of these three components was:sucrose 115 g/L,valley Sodium 59.35 g/L and dipotassium hydrogen phosphate 2.85 g/L.The verification results show that the yield of y-PGA is 41.2 g/L under the optimum addition amount of the above components,which is close to the predicted yield,indicating that the model is more accurate and reliable,and the yield is increased by about 7.9 times compared with that before optimization.The final optimized medium formulation was:sucrose 115 g/L,sodium glutamate 59.35 g/L,dipotassium hydrogen phosphate 2.85 g/L,dipotassium hydrogen phosphate 1.5 g/L,magnesium sulfate 1.5 g/L,Potassium chloride 1 g/L,ferrous sulfate 0.0006 g/L,manganese sulfate 0.025 g/L,copper sulfate 0.00064 g/L.In addition,the fermentation conditions for the production of y-PGA by Bacillus amyloliquefaciens fmbj 37 were optimized,and the optimal fermentation conditions were:culture temperature 33?,liquid volume 30 mL/250 mL,inoculum 2%,culture time 48 h.2.?-polyglutamic acid used as freeze-drying protectant of Lactobacillus plantarum H31The effect of ?-polyglutamic acid on the survival rate of the Lactobacillus plantarum H31 during lyophilization was studied in this study.The results showed that the lyophilization protection was best when the protective agent was 10%skim milk powder,5%trehalose and maltodextrin,and y-PGA.Response surface results showed that when the protective agent formulation was 10%skim milk powder,7.01%maltodextrin,1%trehalose,and 1.13%y-PGA,the powder powder survival rate reached 85.9%after vacuum freeze-drying.3.the preservation of nectar Xiahui No.8 by ?-polyglutamic acidThe experiment of preserving the peaches Xiahui No.8 with y-polyglutamic acid and antibacterial peptide Bacillomycin D(BD)was carried out.The treatment group was 2g/L?-PGA+250mg/L BD;4g/L y-PGA+250mg/L BD;6g/L y-PGA+250mg/L BD;8g/L?-PGA+250mg/L BD.We measured seven quality indicators of peach hardness,soluble solids,titratable acid,soluble total sugar,reducing sugar,weight loss rate and good fruit rate.The results showed that the fresh-keeping treatment group had an effect on Xiahui No.8,which could prolong its shelf life for 2 days,and the fresh-keeping effect was best treated with 8 g/L ?-PGA+250 mg/L BD.