Study On Microorganism And Technique For Soy-sauce Flavor Improvement

The production of soy sauce relates to the collaboration of many beneficial microorganisms, among which the lactic acid bacteria and yeast are the most important ones mainly responsible for fermentating saccharides to yield flavor materials, which is the main route to generate the flavor of soy sauce including alcohols, aldehydes, carboxylic acids, esters and phenols.A halophilous lactic bacteria strain was isolated from the traditional Chinese soy sauce. The morphological, physiological and biochemical characteristics and the 16S rDNA sequence of the screened strain were then analyzed, whose biological properties such as the ability of acid producing, salt tolerance and others were detected. The phylogenetic analysis based on 16S rDNA sequence demonstrated that the screened strain is of the closest relativity to Tetragenococcus halophilus, which basically means that the strain belongs to Tetragenococcus halophilus. The results showed that the screened strain can perfectly produce acid at 35℃and pH 5 while concentration of NaCl was 180g/L. It indicated that the screened strain is very suitable for the carboxylic acid fermentation process of soy sauce , to set the foundation for the subsequent production.A rapid and simple method for determination of volatile flavor components(VFC) of soy sauce was developed by headspace solid-phase microextraction (HS- SPME) coupled to capillary gas chromatography-mass spectrometry (GC-MS). Four parameters, including fiber coatings, extraction time, concentration of salt, and extraction temperature were optimized. The concentrations of the compounds were calculated based on their relative area to the internal standard 2-octanol. The method was characterized by the good repetition within the concentration range of common VFC presented in soy sauce with satisfactory recoveries. An 85μm polyacrylates (PA) fiber was selected as optimum fiber among three different fibers. Optimum adsorption time was 40 min at 45℃while concentration of NaCl was 250g/L. VFC of soy sauce sample were isolated and identified by capillary gas chromatography-mass spectrometry (GC-MS). The result showed alcohols, carboxylic acids, esters and phenols were the major VFC of soy sauce.A stairway fermentation of sauce with multi-microorganisms was primarily studied. The experiment showed the optimal conditions of fermentation. The carboxylic acids formation state was best at 35℃for 8 days with an inoculum ratio of Tetragenococcus halophilus 1%. The alcohols and esters formation state was 30 days at 30℃with an inoculum ratio of Saccharomyces rouxii 0.5% . The rate of mixed multi-microorganisms was Saccharomyces rouxii: Torulopsis mogii at 1:1. It provides a theoretical basis for further industrialized production.