Separation And Purification Of γ-polyglutamic Acid And Its Freezing Resistance To Fish Carp

γ-polyglutamic acid（γ-PGA）is a homopolymer made of glutamic acid and is safe and edible.It has important application value in the food field.In the process of producingγ-PGA by fermentation,due to the strong viscosity of the fermentation broth,separation and purification are difficult and the process is complicated,it is necessary to improve the production process.This article mainly optimized the separation and purification technology of microbial fermentation productionγ-PGA,and studied its application performance in frozen fish gizzards.The results are as follows:（1）Pretreatment of fermentation broth:The effect of temperature and pH on the viscosity of the fermentation broth was analyzed.The results showed that when the fermentation broth pH 3 and temperature were 40°C,the viscosity of the fermentation broth was the lowest,being 0.45 Pa·s.The effect of diatomite and centrifugation on the removal of impurities in the fermentation broth was compared.The results showed that,under the condition of pH3,the fermentation broth was diluted 4 times and the diatomaceous earth was added at 20 g/L.The clarification effect was the best and the loss ofγ-PGA was the lowest.Under this condition,the clarity was 96.3%,the recovery rate ofγ-PGA was 94.31%,and the removal rates of miscellaneous and heteropolysaccharides were 30.79%and 36.92%,respectively.On the other hand,the clarification degree of the fermentation broth after centrifugation at 9000 rpm for 30 min was 84.9%,and the recovery rate was 81.24%,and there was no significant removal ability of the heteroprotein and heteropolysaccharide in the fermentation broth.（2）Decolorization of fermentation broth:The decolorization effects of different decolorization media on fermentation broth were compared.The results showed that activated carbon had better adsorption effect on the pigment in fermentation broth.The results of optimization of the activated carbon adsorption process showed that the decolorization effect of the fermentation broth was best with the addition of 4%of active carbon,the active ratio of particles to powder of 1:3,the decoloration time of 40 min,and the decolorization pH of 2-4.The rate was 87.53%,and the recovery ofγ-PGA was 91.3%.（3）Purification ofγ-PGA:The recovery effects of organic solvent precipitation method and metal ion precipitation method onγ-PGA were compared.The results showed that the effect of ethanol recovery in the organic solvent sedimentation method was best,and after secondary alcohol precipitation,The purity ofγ-PGA reached 88%and the recovery rate was92%.The recoveries and removal effects of metal ions were used as indexes to compare the recovery effects of different metal ions onγ-PGA.The results showed that copper ions had the best precipitation and removal effects,and the purity ofγ-PGA after copper ion precipitation was treated.It reached 91.8%and the recovery rate was 93.3%.（4）The application ofγ-PGA:grass carp surimi as the research object,with salt-soluble protein concentration,Ca²⁺-ATPase activity,gel properties,whiteness and other characteristics as indicators,and using traditional sugar and sorbose as reference,The cryoprotective effect of different concentrations ofγ-PGA on frozen fish carp during cryopreservation at-20°C showed thatγ-PGA can significantly maintain the quality of frozen fish carp.Comparing the effects of different concentrations ofγ-PGA on the freezing effect of surimi,the addition of0.8%γ-PGA had the best effect.After 84 d of cryopreservation,the gel strength of the treated grass carp surimi increased by 82.32%compared with the control group;Protein content and myofibrillar protein Ca²⁺-ATPase activity increased by 47.45%and 70.78%,respectively,compared to the control.These results show thatγ-PGA has a good antifreeze function and can effectively reduce the frozen denaturation of myofibrillar protein during the cryopreservation of grass carp surimi.