Study On The Variation Of Flavor Substrances For Fermentation And Superior Conditions Of Soy Sauce

Currently soy sauce had two main processing technologies, which were the low-salt solid state fermentation and high-salt liquid state fermentation. The former had been commonly used in China because of the short fermentation period, but due to the high fermentation temperature, its flavor became poor. High-salt liquid process in Japan was mature, while the research in China was immature. Flavor of the two brewing soy sauce were very different. For a long time, identification of soy sauce flavor substances had been studied by foreign and domestic scholars, but not flavor's changes of the brewing process.In this paper, head space solid phase micro-extraction (HS-SPME) technique was employed to extract volatile substances from the two kinds brewing process samples, then isolated and identified successfully by capillary gas chromatography-mass spectrometry (GC-MS). Three kinds of high-salt liquid fermentation process were studied by their indices changing, in order to instruct the development of high-salt liquid fermentation in China. With the purpose of enhancing the low-salt solid soy sauce flavor, the response surface methodology was applied to optimize the low-salt leaching pouring process condition. The main conclusions of this study were as follows:1. In this study, qualitative and quantitative methods of flavors were established by HS-SPME-GC-MS. A 75μm Car/PDMS fiber was selected to be the optimum fiber among three different fibers. Optimum adsorption time was 40 min at 50℃. NaCl dosage was 220g/L.2. Analysis solid-state low-salt and high-salt liquid soy sauce flavor ingredients which generated during the fermentation process by the established method, and found that between 15th to 20th days and 45th to 60th days, the content of flavor compounds reached the maximum respectively. And then alcohol, acid concentration decreased significantly, esters and heterocyclic's increased. Totally 76 and 62 volatile compounds were identified from two samples respectively, among which 26 compounds were found in both samples. The compounds contents detected in high-salt soy sauce were significantly higher than the low-salt soy sauce. Ethanol,acetic acid,2 and 3-methylbutanal,3-methylbutanoic acid and phenylacetaldehyde exist in both of them; some new compounds were found that has not been reported before.3. The physical and chemical indicators, sensory evaluation, volatile flavor compounds and 17 kinds of free amino acid contents of three kind of high-salt liquid fermentations were determined to study the effects of fermentation temperature and brine concentration, and found that the positive correlation appeared between decompose ratio of protein and starch, ammonia nitrogen, reducing sugar, red index, total nitrogen and fermentation temperature, but negative with brine concentration. Physical and chemical indicators of 15℃,28℃,41℃fermentation groups reached maximum in 50th,40th and 30th days respectively. Fermentation time cycle could be shortened if fermentation temperature was between 28℃-41℃ammonia nitrogen content and nitrogen utilization increased at the same time. The 15℃,18°Be group' flavor was the best in 9 groups, volatile flavor compounds and 17 kinds of free amino acid contents were the larges and the flavor was the best. Followed was 15℃,18°Be group, its flavor was good, while the 41℃,15°Be group was the worst, and 28℃groups was between the two groups.4. In this paper, the process parameters of low-salt and solid-state fermentation with spraying-extraction were investigated. Setting ammonia nitrogen contents as the response value, the effects of various factors were estimated through variance analysis and response surface analysis. The results showed that optimum fermentation temperature, concentration of brine and spraying-extraction cycle were 43.1℃, 14.8°Be,2.5days respectively. Under these conditions, the ammonia nitrogen content of soy sauce was 1.15g/100mL.The experimental values agree with those predicted from the regression model within RSD<2%, indicating a good fitness. Ammonia nitrogen content increased 20% by optimization process.5. The solid-state low-salt soy sauce with spraying-extraction fermented after optimization, ammonia nitrogen, total nitrogen contents and nitrogen utilization increased 0.1 g/100mL and 8% respectively than the control group. Flavor substances types and concentrations were increased also, especially acids, alcohols and furan.