Study On Walnut Peptides Prepared By Integration Of Solid State Fermentation And Enzymolysis Based On Magnetic Field Strengthening And In-situ Monitoring

Walnut meal is a by-product after walnut oil extraction.The walnut protein is nutrious,which accounts for more than 45% in walnut meal.However,due to lacking deep processing technology,the value of walnut meal cannot be fully developed.Walnt peptides can be prepared by microbial fermentation and enzymolysis from walnut meal,which greatly improves the availability of protein resource and increases the value.In this study,magnetic field were applied to enhance fermentation to accelerate the growth of microorganisms,then the method of enzymolysis followed to increase the conversion rate of the protein,meanwhile an in-situ monitoring system and spectral acquisition method for enzymolysis were established to support an intelligent control method for the enzymolysis process.Therefore,this study provides important theoretical support for the efficient and intelligent value-added processing of walnuts meal.The main work and conclusions were as followed:(1)Study of solid-state fermentation of walnutmeal meal:Solid state fermentation with Bacillus subtilis 10160 and Aspergillus niger GIM 3.452.Single-factor step-bystep optimization was performed to select optical fermentation time,raw material particle size,fermentation temperature,inoculum quantity,material/liquid rate,etc.The fermentation process parameters of two strains were obtained: the solid fermentation conditions of Bacillus subtilis 10160 were fermentation time of 3 d,raw material particle size of 40 mesh,material/liquid rate of 1:1.25,inoculum quantity of 5% and the fermentation temperature of 28°C.Under this condition,the peptides content after fermentation was 24.40%,which was 382.92% higher than that of raw material of 5.02%.As for Aspergillus niger,the best fermentation parameter were fermentation time of 4 d,material particle size of 40 mesh,the fermentation temperature of 28°C,the inoculum quantity of 15% and material/liquid rate of 1:1.25.After fermentation,the peptides content was 15.86%,which was 213.95% higher than that of raw material of 5.02%.According to peptides content after fermentation by these two strains,Bacillus subtilis was a better candidate for fermentation.(2)Study of magnetic field assisted solid-state fermentation :Based on the optimized solid-state fermentation process parameters,the process parameters of the magnetic field were explored through the single-factor test.The molecular weight distribution,the content of peptides and protein were analyzed.The enzymolysis method optimizes the enzymatic hydrolysis process parameters after fermentation.Optimum process parameters of magnetic field assisted solid state fermentation by Bacillus subtilis were magnetic field treatment intensity of 50 Gs,magnetic field treatment time of 3 h,magnetic field intervention time of 0 h,magnetic field treatment frequence of once per day.Peptides content increased by 14.13% after magnetic field assisted fermentation.(3)Study of enzymolysis after fermentation :In the process of whole product after fermentation,the best enzyme was Alkaline protease,and the optimal parameters for enzymolysis were: substrate concentration of 25 g/L,enzyme dosage of 400 U/g,and enzymolysis time of 60 min.Under this condition,the supernatant peptides content was 17.03±0.07 mg/m L,and the peptides yield could reach 68.12%.(4)Study of in-situ monitoring technology during the process of enzymolysis :An in-situ monitoring system and spectral acquisition method for enzymolysis of walnut peptides after fermentation were established.In the process of extraction-enzymolysis,near-infrared spectra were compared by Savizky-Golay(SG),Standard Normal Variate transformation(SNV),First Derivatives and Second Derivatives.The extraction and enzymatic model were established by Partial Least Square(PLS)method and Synergy interval Partial Least Squares(Si-PLS)method.The models were evaluated by correlation coefficient and root mean square error of the model.The results showed that the SNV had the best modeling effect in spectrum pretreatment.The Si-PLS method had a correlation coefficient of prediction of 0.9931 and a root mean squared error of prediction of 0.858 mg/mL.An accurate prediction effect was achieved.All these results provided a theoretical foundation for the intelligent production of magnetic field assisted solid-state fermentation of walnut peptides.