| Amino nitrogen and urethane are the main factors affecting the quality of Huangjiu.Increasing the amino nitrogen content in Huangjiu and reducing the urethane are the technical bottlenecks in Huangjiu production.As amino acids are important precursors of urethanes,colleagues who increase amino nitrogen content need to reduce urethane production.Screening strains with high protease activity and strains for urea utilization,and reducing urea content is one of the main ways to reduce urethane production,and has great application prospects.In this project,The target strain was selected,optimized the koji-making process,optimized the fermentation process,and double-bacterial fermentation to increase the amino nitrogen production and reduce the urethane content.(1).Through the selective culture of milk medium,a strain CX1 with high protease activity was selected,The amino nitrogen content in the fermentation product was 1.1 g/L.and the sequence alignment was identified as Aspergillus flavus.Sequence alignment identified the strain as Aspergillus flavus.By selecting the culture medium and conducting urea content detection and re-screening,a urea utilization strain CS1 was obtained,the urea utilization rate was 56%,and the sequence comparison was identified as Saccharomyces cerevisiae(2).Using the CX1 strain,optimize the amino nitrogen in the koji making process through the Central Compound Design(CCD)and BP neural network coupled genetic algorithm.The central compound(CCD)test design was used for optimization.Under the optimal conditions,the amount of water added was 9.50 ml,the inoculated amount was 15.50 ml,and the amount of bran was 21.00%.The amino nitrogen content was 1.39 g / L.After optimization,the amino nitrogen content increased by 148%.Neural network coupled genetic algorithm optimizes optimization,and the best conditions for making koji are water addition 9.50 ml,inoculation 14.50 ml and bran addition 27.00%.At this time,the amino nitrogen content is 1.40 g / L.Amino nitrogen production increased by 150%.The output and accuracy of neural network optimization prediction results are higher.(3).Using Box-Behnken Design(BBD)and neural network coupled genetic algorithm to optimize the yield of amino nitrogen in the Huangjiu fermentation process,fermentation was carried out under the conditions of soaking time 25 h,addition amount 12.00 ‰ and fermentation time 11 d to obtain The content of amino nitrogen is 1.54 g / L,the difference between the theoretical value and the actual value is 0.05 g / L.Neural network coupled genetic algorithm was used to optimize the optimization.The experiment was repeated three times under the conditions of soaking time 28.50 h,addition amount 11.50 ‰ and fermentation time 11.50 d.The amino nitrogen content was 1.62 g / L,which was different from the actual value 0.02 g / L.Compared with the optimization of the koji making process,the yield of amino nitrogen increased by 15.7%.Through dual process optimization,the output was eventually increased by 189%.(4).By reconstituting the strain CS1,the resulting Huangjiu contains amino nitrogen content 1.58 g / L,urea content 20 ug,urethane content 17.52 μg / L,alcohol content 11.1 vol%,sugar content 81.79 g / L and The p H is 4.21.It complies with the Huangjiu industry standards,and the testing indicators comply with the national Huangjiu testing standard GB / T 13662-2018.It is a novel attempt to improve the quality of Huangjiu by increasing the yield of amino nitrogen in Huangjiu and reducing the yield of urethane,and using urea to reduce strains of urethane.It has important practical significance for improving the quality of Huangjiu. |
