Study On Flavor Recognition Of Fermented Soy Sauce And Its Metabolic Mechanism

Originated in China more than 2500 years ago,fermented soy sauce has become one of the most widely accepted condiments in southeast Asian countries.Today,China's annual output of soy sauce is about 8.5 million tons,accounting for more than 65 percent of the world's total production,and the number is still growing steadily.At present,due to its unique taste and aroma,not only in China,Japan,South Korea and Thailand in southeast Asia,but also in Western Europe,the popularity is growing rapidly.In recent years,with the development of the catering industry,the consumption per son in soy sauce is gradually increasing,and the market demand for high-quality soy sauce is also increasing,which speeds up the upgrading speed of soy sauce and accelerate the further scientific research on soy sauce.In this study,a rapid and accurate method for identifying four different qualities of soy sauce was developed by using a variety of detection methods,and a fast quantitative prediction model of amino acid nitrogen in soy sauce was established.The flavor characteristics of brewed soy sauce with different qualities were also studied,including the key smell substances and the key taste substances?amino acid level?.Finally,the flavor of traditional fermented soy sauce was studied,and the metabolic mechanism of fermented soy sauce was proposed.The details are as follows:Firstly,despite soy sauce has been one of the most popular seasonings in eastern Asia,rapid and holistic methods for its authentication and discrimination are still lacking.This research is sought to develop a novel method for rapid discrimination and amino nitrogen quantitative evaluation of different quality of soy sauces?Chinese traditional fermentation soy sauce?CTFSS?,Japanese traditional fermentation soy sauce?JTFSS?,high-salt liquid-state fermentation soy sauce?HLFSS?and low-salt solid-state fermentation soy sauce?LSFSS??based on tri-step IR and partial least squares?PLS?.Global nutrition fingerprints?saccharides,proteins,amino acids and other compositions?of each quality soy sauce at the three levels of enhanced spectral resolution and nutrition profile variations among different soy sauces are synthetically interpreted with fast evaluation of their relative contents based on spectral peak intensity.Complementarily,electronic sensory combined with SPME-GC-MS distinguishes four species soy sauces effectively in smell with discrimination indexes 90.Specifically,FT-IR peak intensity at about 1409 cm^-1?C-N band?exhibits regular enhancement with the increasing concentration of amino acid nitrogen.Thus,a quantitative prediction model based on IR spectra is established by PLS?R²,0.9956;RMSEC,0.233?.It has been demonstrated that the developed method is applicable for rapid?5 min?discrimination and quantitative analysis of amino acid nitrogen in soy sauce.Secondly,OAV?odor activity value?and TAV?taste activity value?were used to study the key taste or odor substances in Chinese traditional fermented soy sauce?CTFSS?,Japanese traditional fermented soy sauce?JTFSS?and high-salt liquid-state fermentation soy sauce?HLFSS?.The results showed that there were significant differences in the key odor substances of different kinds of soy sauce.The OAV value of CTFSS was higher than other kinds of soy sauce.In addition,the most critical odor substance in CTFSS is 3-methyl-butyraldehyde with almond and nut odor,and the most critical odor substance in HLFSS is phenyl acetaldehyde with rose fragrance and osmanthus fragrance,while the most critical odor substance in JTFSS is phenyl ethanol with honey and rose odor.From the perspective of amino acid taste,it is found that the most important flavor in soy sauce is umami,which is almost 10 times as sweet taste and 15 times as bitter taste.Meanwhile,the content of amino acids in traditional CTFSS was significantly higher than that in other kinds of soy sauce.Finally,soy sauce,a famous seasoning in Asia and throughout the world,composed with many flavor substances and metabolites that were produced during the fermentation process.To obtain a global understanding of the metabolic mechanism having highly impacts on soy sauce flavors and quality,flavor and metabolic compounds changes of a Chinese traditional soy sauce?CTFSS?associated with fermentation time up to 10 years were comprehensively investigated.Glutamic acid?Glu?and aspartic acid?Asp?were prominent in different fermented time soy sauce.Significant drops in the amino acid content occurred from 5M?5-months soy sauce?to 10M?10-months soy sauce?,which were principally associated with the faster conversion rates between amino acids and volatile substances or Maillard reactions products than those of proteins degradation to amino acids and starch degradation to sugars.Continuous decrease in the content of hypoxanthine?Hx?was found from 1M to 7M,and it tended to be stable after 7M.Moreover,phenols,esters,alcohols,and benzenes were mainly produced from 5M to 9M;aldehydes,ketones and acids were mainly increased from 1M to 5Y.Elevated 3-meth-butanal and 4-ethylphenol from 5M to 9M were attributed to the Strecker degradation of Val,Ile and Leu or the degradation of aromatic amino acids.In summary,a subtle trilogy mechanism in soy sauce metabolism was proposed.Step 1:starch and proteins degraded into sugars and amino acids;Step 2:amino acids and sugars converted into Maillard reaction products or other volatile substances;Step 3:a delicate balance between Step 1 and Step 2 was established and promoted or inhibited each other.These findings had potential guiding significance for improving fermentation process to enhance or even regulate the flavor and the quality of soy sauce.