| Succinic acid is one of taste compounds in the soy sauce,the higher the content,the better the flavor.At the same time,succinic acid has many benefits to human body,can enhance human function,promote human metabolism,so adding succinic acid in soy sauce is more conducive to human health.Aspergillus oryzae AS3.042 was used as the original strain in this paper,to filter Aspergillus oryzae which could produce abundant succinic acid by mutation and was used in soy sauce fermentation,in order to enhance the ability of Aspergillus oryzae to secrete succinic acid during fermentation,to increase the concentration of succinic acid in soy sauce,to improve the quality of soy sauce,the main research contents and results are as follows:(1)Aspergillus oryzae AS3.042 was selected as the original strain and use Aspergillus oryzae spore protoplast as mutagenesis material,Aspergillus oryzae was screened by secondary ultraviolet mutagenesis,secondary nitrosoguanidine mutagenesis and combination of ultraviolet and nitrosoguanidine mutagenesis.The mutated strains by shake flask culture which was induced by these three mutants succinic acid content is1.54g/L,0.83g/L and 2.86g/L,respectively.Among them,the mutated compound strain ASQ-1 is best,which was 294 times higher than that of the original strain,and it is genetic performance was stable.(2)To optimize of Aspergillus oryzae koji culture medium.Soybean meal,bran,wheat flour and barley flour were used as raw materials for koji.Soybean meal is protein source,the others are starch source.Then,to apply Design-Expert 8.0.6.1 Simplex Centroid optimized raw materials formula.The conditions of koji were moisture content52%,inoculation volume1.6×10~6 units/g,and culture time 72h.Experimental results show that Soybean meal:bran=0.6:0.4 is the best,the yield of succinic acid was the highest.Experimentally verified,the content of succinic acid in is 14.07 g/kg in koji.(3)The optimization of preparation conditions for Aspergillus oryzae ASQ-1 strain to produce koji.The single factor experiment was used to optimize the three conditions of water content,inoculation quantity and culture time.Experimental results show that,the optimal result is water content52%,inoculation quantity 3.2×10~6 units/g and culture time 84 h.According the condition to test,the content of succinic acid is 16.10 g/kg and it is 14.43%higher than before optimization.According to the single factor test,response surface method was used to optimize the preparation conditions of ASQ-1 strain,the optimum technological condition is cover the moisture content was 52%,the incubation time was 89 h and the inoculation volume was 3.3×10~6 units/g.The concentration of succinic acid was 16.72 g/kg,higher than that of control strain 7.75 g/kg.The experimental results showed that the yield of succinic acid could be increased effectively under optimized conditions.(4)The application of Aspergillus oryzae ASQ-1 strain in soy sauce brewing.According to the conditions,to make Aspergillus oryzae ASQ-1 and Aspergillus oryzae AS3.042 koji at the same time,then to fermentation as high salt dilute state process.After detection,the content of succinic acid in the Aspergillus oryzae ASQ-1 raw sauce fermented for 3 months was 0.488g/L,6.5 times higher than the control under the same conditions.To contrast other physical and chemical indicators found that total acid,pH,and amino acid nitrogen are identical and soluble salt-free solids is similarity,ammonium salt and total nitrogen were slightly lower than the control,both of which met the national standard.It can be seen from the above result that the application of ASQ-1as a strain for industrial production of soy sauce fully meets the requirements,and at the same time,it can also improve the content of succinic acid in soy sauce,so it has a broad application prospect in the field of food. |
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