Identification And Application Of Exclusive Flavor Lactobacillus Spp. And Staphylococcus Spp. Isolated From Traditionally Dried/cured Nemipterus Virgatus

To sutdy the microflora of dried/cured Nemipterus virgatus which affects the flavor of traditional cured fish, the dominant microorganisms had been isolated and identificated for the rapid formation of cured fish to get the unique flavor.Commercial strains of Lactobacillus spp. and Staphylococcus spp. were inoculated in fermentation optimization experiments, and a quick maturation process was created. Sensory analysis, chemical analysis and instrumental analysis were used to study the difference between the control sample, purchased strains and isolated strains fermented samples to establish the initial flavor evaluation system of dried/cured fish.The major results are:(1) Lactobacillus spp. and Staphylococcus spp. were isolated from Beihai light cured fish and then identified. 13 Lactobacillus spp. and 10 Staphylococcus spp. were isolated. After physiological and biochemical analysis, 3 Lactobacillus spp. and 2 Staphylococcus spp. were left, and had identified into a genus level using conventional microbiological methods as Pediococcus pentosaceus,S5 is Staphylococcus carnosus,S8 is Staphylococcus xylosus. The growth curve of 24h and acid production capacity were tested, the acid production capacity of Staphylococcus S8 is better than lactic acid bacteria. By cured in liquid medium supplemented with 5% NaCl, strains can be selected to achieve stability in a shorter time period, and gets more cells.(2) Optimization of fermentation process.In order to improve the flavor and texture of cured fish products, cured fish is fermented by Pediococcus pentosaceus and Staphylococcus xylosus.The suitable synthesis conditions were defined as follows: fermentation temperature, 35℃; fermentation time, 10h; the ratio of Pediococcus pentosaceus and Staphylococcus xylosus, 1/2 by response surface analysis. After fermentation products aromas, freshness, good aftertaste and texture have been improved.(3) Established the relationship between dried/cured fish flavor quality and physical and chemical indicators.Correlation analysis, regression analysis, statistical analysis and principal component analysis were used, and show that in addition to total acid, water, salt, volatile basic nitrogen, soluble protein and amino nitrogen content and TBA value of such ingredients were obvious correlate with flavor quality, which can be used for indirect evaluation of the above ingredients. The flavor quality of cured fish is comprehensively evaluated from seven indexes of taste, umami, rancid, texture, bite strength, color, sour and fishy. The equation established by regression analysis to the main ingredients for parameter could well describe the quality of cured fish flavor. To ensure the quality of cured fish flavor, moisture content of products should be controlled at 57.80% ~ 60.86%, amino nitrogen content≥0.80mg / g, 6.52≤pH≤6.67, soluble protein content≥99.60mg / g, 33.90≤TBA≤38.40, 0.85%≤total acid≤1.10%.(4) The high similarity of types and content of main taste components between control sample and fermented samples had been confirmed.The electronic nose were used to compare purchased sample, purchased strains and isolated strains fermented samples. The differences between three kinds of samples is not large, few of sensory signals is different,The fermented samples is a good replica of fragrance to purchased sample. SQC statistica shows that isolated strains fermented samples is closer to purchased samples. Solid phase microextraction(SPME) and gas chromatography-mass spectrometr(GC-MS) were used to analysis the effects of fermention to volatile compounds in fish meat of Nemipterus virgatus. 63,69 and 66 volatile compounds were identified by comparing their mass spectra with those contained in the NIST mass spectral database respectively.Among these compounds carbonyl and alcohols were the major flaovr components and the content and species is similar of purchased sample and purchased strains fermented samples.To sum up, the application of bio-catalytic technology by inoculated with microorganism for fermentation, simulate the flavor of traditional cured fish.Flavor evaluation system was set up successfully.