A Study On Multi-microorganism Stepwise Fermentation Process And Flavor Profile Change Of Scallop Skirt Sauce

In order to increase the utilization rate and the added value of scallop skirt, a fermentation process using scallop skirt as raw material, and sterilized soy meal and Aspergillus oryase 3.042 as starting culture was studied. At later stage of the fermentation, Tetragenococcus halophilus and Zygosaccharomyces rouxii were inoculated to improve the flavor and taste of the scallop skirt sauce. The fermentation parameters were optimized to develop a nutritious scallop skirt sauce with balanced flavor profile. The main results were listed as below:1. Study on multi-microorganism stepwise fermentation process. (1) Protein hydrolysis fermentation process: Starting culture was made by inoculating Aspergillus oryzae to soy meal (autoclaved at 0.1Mpa for 30min, cooled to 35 degrees C) at 0.05% level, and incubating at 30 degrees C for 36h. Scallop skirts were blanched in boiling water, cooled and minced. The minced scallop skirts were mixed with the starting culture at 4:1 ratio, and fermented with protease (2000U/g), and salt (12% by total weight) in a sealed beaker at 40 degrees C. (2) Aroma fermentation process: After fermentation for 8 days, activated Tetragenococcus halophilus was inoculated at 1% level. The fermentation was continued for another 6 days at 30 degrees C. The scallop skit sauce was then inoculated with activated Zygosaccharomyces rouxii (1% level), incubated at 30 degree C for 7 days, ground and sterilized to make the final product.2. Analysis of flavor profile changes during the stepwise scallop skirt sauce fermentation process, using headspace solid-phase microextraction and gas chromatography - mass spectrometry method. Tetragenococcus halophilus fermentation increased contents of acid compounds, especially of acetic and lactic acid. Further formation with Zygosaccharomyces rouxii effectively inhibited the formation of acid compounds, and promoted the esterification. As a result, the flavor profile of the final product was improved by increased level of esters and decreased level of acids. The main volatile compounds in the scallop skirt sauce included ethanol, ethyl acetate, 3-methyl butyrate, 2-methyl butyric acid ethyl ester, ethyl lactate, phenylacetaldehyde, 2-methyl butyric acid, 3-methyl butyraldehyde, palmitic acid ethyl ester, 3-methyl ethyl butyrate, and 2-methyl butyraldehyde. These compounds were the main flavor components, and accounted for 76.45% of total volatiles in scallop skirt sauce.3. Nutritional profile analysis of the scallop skirt sauce. The scallop skirt sauce contained 19.85% of protein, 0.80% of fat, and 1.75% of amino acid nitrogen. The nutritional profile showed that the scallop skirt sauce is high in protein, and low in fat and sugar. 4. Free amino acid profile analysis of the scallop skirt sauce. The total free amino acid content was 9.82g /100g. The free total essential amino acids content was 4.15g /100g. The sauce contained relatively high level of sour and umami amino acids, Glu and Asp (19.34% of total amino acids). The sweet and umami amino acids (Thr, Ser, Ala, Gly, Pro, Lys) accounted for 38.8% of total amino acids. These amino acids are the main contributors to the taste of the scallop skirt sauce.5. Sensory analysis and microbiological analysis of the scallop skirt sauce. The scallop skirt sauce was a brown paste with smooth texture and rich seafood flavor. All microbiological indicators met national standards.