Flavor Improvement Of Enzymatic Extracts Of Pinctada Martensii Entrails By Liquid Fermentation Combination With Staphylococcus Xylosus And Lactobacillus Plantarum

Pinctada martensii entrails, an important low-valued protein resource in our country, are not yet fully utilized. Its enzymatic hydrolysate, which is tasty, nutritive and haves various physiological activities, is ideal for the development of natural functional seafood seasoning. However, there are still many defects in the flavor of the enzymatic hydrolysate, such as with a strong fishy smell and a poor aroma. In this thesis, the optimum condition for flavor improvement of the enzymatic extracts from Pinctada martensii entrails by microbial fermentation was studied, its effects on volatile and non-volatile flavors,which were evaluated with sensory evaluation, chemical analysis and instrument analysis, expecting to provide theory foundation for the development of high-grade seafood seasoning using Pinctada martensii entrails.1. On the basis of single factor experiments, Box-Behnken combination of design was used to optimize fermentation process for Pinctada Martensii enzymatic hydrolysates and to study the effects of four independent variables as follows: the proportion of Staphylococcus xylosus and Lactobacillus plantarum, fermentation temperature, fermentation time and seeding amount. The results suggested that the most excellent conditions were the proportion of Staphylococcus xylosus and Lactobacillus plantarum 3:1,seeding amount 3%, fermented for 20h under 30℃,the flavor of the enzymatic hydrolysates was improved markedly, and the enzymatic hydrolysates were endowed with fermented flavor.2. The volatile flavors of Pinctada Martensii enzymatic hydrolysates before and after fermentation were acquired by sensory evaluation and electronic nose technology, the results showed that the volatile flavors had a significant change. the fishy smell was weakened quite effectively, the shellfish flavor was intensified and fermented flavor was produced by fermentation, electronic nose had also similar to the results, the response intension of the sensor on odor of fermentation of Pinctada Martensii enzymatic hydrolysates was more than odor of Pinctada Martensii enzymatic hydrolysates. Volatile flavor compounds in before and after fermentation of Pinctada Martensii enzymatic hydrolysates were extracted by headspace solid phase microextraction (HS-SPME),and were analyzed by gas chromatography-mass spectrometry (GC-MS). Totally 77 volatile compounds were identified from two samples, among which 25 compounds were found in both samples, but other 17 compounds were found in only Pinctada Martensii enzymatic hydrolysates sample and only 36 compounds in fermentation of it sample. Further,the flavors of Pinctada Martensii enzymatic before and after fermentation hydrolysates were evaluated.3. Taste compounds of Pinctada Martensii enzymatic hydrolysates before and after fermentation were analyzed by chemical and instrument analysis.The main flavor components including betaines,free amino acids,lactate,succinic acid,nucleotide-related compounds,sugar and inorganic ions and such as K+,Na+,PO43- and Cl-, were determined and compared. Results showed that after the mixed fermentation,the content of amino acid and succinic acid increased by 17% and 26%,the content of betaine, nucleotides and related compounds reduced by 21% and 2%, but they still maintain a high concent;while the content of sugar were reduced by 36%, due to the content of sugar in Pinctada Martensii enzymatic hydrolysates before and after fermentation was a little, and didn't effect on the overall flavor;the content of inorganic ions haves little change.4. Peptides were the major components before and after fermentation of Pinctada Martensii enzymatic hydrolysates.Therefore, separation and analysis of them. At first, Pinctada Martensii enzymatic hydrolysates before and after fermentation were separated by ultrafiltration,we obtained separately 5 different molecular weight fractions in the two samples, and the different molecular weight of the components of the two samples were selected two samples of molecular weight 1-3KDa of the components by sensory evaluation, which had strong umami.Then the components of the molecular weight of the two samples were separated by macroporous resin,then obtained separately four components, the component B of Pinctada Martensii enzymatic hydrolysates had strong umami thick, the component B Pinctada Martensii enzymatic hydrolysates by fermentation also had strong umami thick, and the component C had fast umami.