Study On The Effect Of Mixed Cultures Fermentation On The Quality Of Soy Sauce

Soy sauce koji-making is one of the key points in soy sauce brewing process,the quality of koji directly determine the formation of nutrition and flavor.The improvement of protein utilization rate and flavor of soy sauce were the urgent problems to be solved.This reseach focused on the chenges of physical and chemical properties of soy sauce samples which were fermented by using Aspergillus oryzae B-2&A.niger Z-3 and B-2&A.niger FND-A47 mixed cultures in koji-making and the low-salt solid-state fermention technology.The main research contents of this dessertation are as follows.(1)A.niger FND-A47 and Z-3 strains were selected by an indicator of acid protease activity,then two A.niger strains were separately mixed with A.oryzae B-2 at 6 different ratios.The result showed that the acid protease activities were enhanced with an increase of 10.83%and 26.73%respectively compared to that of the monoculture of A.oryzae B-2.(2)Comparison of mixed cultures koji-making and monoculture koji-making.The acid,neutral and alkaline protease acivities at 36 h in the mixed koji of of B-2&FND-A47 at 3:1 ratio were respectively improved by 27.17%,38.72%and 27.18%compared to those of B-2 monoculture.However,the 3 kinds of protease activities from samples fermented by B-2&FND-A47 and B-2 monoculture were approximately same at 42 h.(3)The physical and chemical properties of soy sauce samples from B-2&FND-A47 and B-2&Z-3 were assayed and analyzed.The indicators such as total nitrogen,total acid,amino nitrogen and reducing sugar were increased at specific mixture ratios.The glutamic acid and free amino acids contents in samples of B-2&FND-A47 were enhanced by 78.12%and 53.53%than those of B-2 monoculture.Meanwhile,the glutamic acid and free amino acids contents in samples from B-2&Z-3 were enhanced by 33.25%and 38.80%than those of B-2 monoculture.The 17 and 25 types of flavor compounds in soy sauce from B-2&FND-A47 and B-2&Z-3 were respectively identified and determined by headspace solid phase micro extraction and gas chromatography mass spectrometry.(4)The free amino acids,organic acids and volatile flavor compounds were selected to calculate the general evaluation index scores basing on the principal component analysis,and were confirmed that the optimal mixture ratio were 4:1 for both B-2&FND-A47 and B-2&Z-3.(5)The 42(B-2&FND-A47)and 37(B-2&Z-3)types of volatile flavor compounds were determined respectively by employing the electronic nose.Some important substances,such as guaiacol,4-ethyl guaiacol and HEMF,were detected.The contents of methanol and acetaldehyde reached the highest respectively in soy sauce of B-2&FND-A47 and B-2&Z-3.Thus,this result not only impacted that the different A.niger strains had various influence on flavor character of soy sauce,but also proved that electronic nose had the accuracy and repeatability for rapid detection of volatile flavor compounds from soy sauce.