Breeding Of High-yield Strain For Polyglutamic Acid Production From Pea-protein Wastewater And Optimization Of Production Technology

As a biopolymer substance,?-polyglutamic acid??-PGA? has good water solubility,biocompatibility,non-degradability and non-toxicity.It is widely used in medicine,food,cosmetics,agriculture and other fields.In this paper,as the main raw material,pea-protein wastewater was used to produce the ?-PGA.And we determined the characteristic parameters of pea-protein wastewater.A high-yield strain was screened from natto.The fermentation culture conditions were optimized by a shaker experiment.Then the production process parameters were further optimized using 10 L and 3 t fermenters.The effect of application of ?-PGA was verified by germination experiment and chelate calcium experiment.1?We measured batches of pea-protein wastewater.The pH is 4.95?5.21,the solid content is 1.5?4% by the drying method,the protein content is 0.55?0.98% by Kjeldahl method,the reducing sugar is 0.58?0.91% by potassium permanganate titration method and the COD is 15?20 g/L by dichromate method in wastewater.Protein waste water consists of two parts:one is the upper layer of whey separated from the starch waste liquid;the other is the curd washing wastewater.Therefore,the composition of protein wastewater is affected by the previous production process,and the solid content of the wastewater fluctuates,but the pH value is more stable than the carbon to nitrogen ratio.2?A high-yield strain of ?-PGA production named LD-9308 was selected.And this strain was identified as Bacillus subtilis according to the morphology,physiology and biochemistry property.The optimal fermentation was obtained by shaking-bed culture,single factor experiment and orthogonal design.And the optimum fermentation medium was obtained as follows:2% glucose,5% sodium glutamate,0.3% K₂HPO₄,pH 7.5,time 26 h.Based on the shaker experiment,we carried out the expansion of the fermenter,and determined the growth of bacteria by single factor experiment.The optimum fermentation scheme was:fermentation time 22 h,rotating speed 220 r/min,pH 7.5,inoculation volume 1%,37?.The maximum yield was 53.7 g/L.3?The effect of application of ?-PGA was verified by germination experiment and chelate calcium experiment.?-PGA can promote seed germination and growth,and can effectively prevent the combination of sulfate and calcium to form poorly soluble substances.It can promote the dissolution of metal salts in the soil and improve the absorption and utilization of trace elements.