Comparison Of Different Aspergillus Oryzae Strains' Enzyme Profiles And Their Effects On Flavor Quality Of Soy Sauce

Soy sauce is an important condiment in Asia,and welcomed by people all over the world.Soy sauce,with umami and salty characteristic and rich flavor,was produced by microorganisms such as Aspergillus oryzae after a long period of fermentation;during the process,the protein,starch,lipid and other nutrients were degradated and their products were interacted with each other.For many years,the screening index of Aspergillus oryzae was protease activity,because the classification of soy sauce grade in GB/T 18186-2000 mainly depended on the content of amino acids nitrogen,and the protein utilization rate was the focus of the industry.However,the study about other enzyme acivities of Aspergillus oryzae was relatively rare.Some studies have shown that protease was the base of soy sauce fermentation,and other enzyme profiles had the influence on the flavor quality of soy sauce,but the relationship was not clear.Therefore,this paper aims to study the enzyme profiles of different strains of Aspergillus oryzae,and their influence on the flavor quality and components accumulation of soy sauce.The main contents were as follows:(1)The differences of growth morphology and 9 enzyme activities among 7 strains of Aspergillus oryzae were determined in this study.The results showed that the enzyme profiles of Aspergillus oryzae could be divided into two types: CA-1,CA-3,CA-4,CA-7(Group A)had an advantage in degrading proteases,including neutral protease,acid protease and aminopeptidase;While Group B(CA-2,CA-5 and CA-6)had relatively higher activities of carbohydrates-degraded enzymes,Saccharification enzyme,Amylase,Glucosidase,Xylanase,and lower activities of protein-degraded enzymes.There were correlations between different enzyme activities,for example,high correlations were found between saccharification enzyme and amylase(r=0.90),aminopeptidase and acidic protease(r=0.78),and aminopeptidase and pectinase(r=0.97).In addition,the correlation among protein degradation enzymes(neutral protease,acidic protease and aminopeptidase)was 0.72.(2)The flavor and material basis of different high-salt liquid soy sauce with 7 strains Aspergillus oryzae were detected.The results were obtained by amino acid analyzer(free amino acids profiles),GC-MS(volatile profiles),QDA and electronic tongue(sensory evaluation),respectively.The results showed that the total nitrogen,amino acids nitrogen,reducing sugar and maillard reaction products showed increasing trends during the fermentation process,while the reducing sugar in part of samples decreased in the late fermentation period.Overall,the umami and sweetness of group A fermented soy sauce were weaker than group B,which resulted from the free amino acid composition.And group A was higher content in acid aroma components,stronger taste in sour and richness(p < 0.05).While the content of alcohols,esters,aldehydes aroma composition of group B fermented soy sauce is higher,and salty,umami taste of it was stronger performance(p < 0.05).(3)Based on multivariate data analysis,the relationship between the enzyme profiles of Aspergillus oryzae and the flavor quality of fermented soy sauce was discussed.The result showed that pectinase,aminopeptidase and acidic protease were correlated with the enhancement of sour taste(p < 0.05),and the accumulation of aroma substances such as fumigation,fruit flavor and malt aroma.Xylanase and amylase were significantly correlated with umami and saltiness(p < 0.05),and were associated with aroma substances such as flower and fruit aroma,malt aroma,smoked aroma,baked aroma,etc.Overall,the relationship between enzyme profiles and flavor quality of soy sauce is more regular,compared with that of enzyme profiles and aroma quality.So the data from the enzyme profiles and tastes was constructed in MLR model,to verify the regulation effect of taste of soy sauce through the addition of exogenous enzymes.The result showed that improving xylanase enzyme activity of koji,could improve the umami taste of fermented soy sauce(p < 0.05),which consistented with predict results of MLR model.