Effects Of Mixed Starter Cultures And Exogenous L-Lys On The Quality Of Fish Paste Using Longsnout Catfish By-Products

In 2016,the production of longsnout catfish farming in China has reached about 286,000 tons.However,at present,the processing of longsnout catfish mainly consists of frozen fish fillets,which will produce a large amount of fish meat by-products.It greatly causes waste of resources and environmental pollution.Fermented aquatic products are favored by consumers because of their unique flavor.The condiment was gained by fermenting the by-products such as longsnout catfish.It can not only effectively improve the comprehensive utilization rate of longsnout catfish,but also solve the problem of waste of resources and alleviation of environmental pollution.In this study,the mixed starter cultures were prepared by screening moderately halophilic bacteria,and a rapid fermentation process of longsnout catfish was established.The effects of mixed starter and exogenous L-Lys on the flavor and nutritional characteristics of fermented fish pastes were investigated.Finally,high quality fish paste was developed.This study provides theoretical basis and technical guidance for improving the comprehensive utilization of longsnout catfish.The main findings and results are as follows:1.Screening,identification,growth characteristics and enzymatic properties of halophilic bacteria in traditional fermented shrimp paste.The moderately halophilic bacteria of producing proteases from traditional shrimp paste were isolated and identified,and six strains of protease-producing moderate halophilic bacteria were isolated.The identified strains belonged to two genera of Halobacillus and Bacillus.There are six species of Halobacillus campisalis,Halobacillus halophilus,Halobacillus faecis,Bacillus altitudinis,Bacillus aquimaris,Bacillus hwajinpoensis.The optimum salinity of the 6 strains was 5% and the salt tolerance range was wide,all of them belonged to moderate halophilic bacteria.They grew well in 25-37?,except zzy7 was a halophilic acidophilic strain,the other 5 strains were halophilic and basophile strains.The activities of proteases produced by 4 strains of halophilic bacteria were high and reached the highest at 50?,and the activities of proteases produced by 4 strains were salt-tolerant and could be used in salt-fermented aquatic products.2.Optimization of the process of rapid fermentation of fish pastes with mixed starter cultures.The optimal inoculation ratio was determined to be 1:1:1:1 by measuring the effects of the inoculation ratio of mixed strains(Halobacillus campisalis,Halobacillus faecis,Bacillus aquimaris,Bacillus hwajinpoensis)on the amino acid nitrogen and sensory evaluation of the fermented fish pastes.Basing on single factor experiment,the effects of fermentation temperature,salt,mixed starter cultures and fermentation time on the sensory quality of fast-fermented fish pastes were optimized by orthogonal test.The results showed that the best combination of fermented fish pastes was fermentation time of 15 d,fermentation temperature of 37?,6 log CFU/g of mixed starter cultures and 12% NaCl.3.Effect of mixed starter cultures and exogenous L-lys on the quality of fermented fish pastesBased on the best process of fermented fish pastes,the fish paste was divided into three groups,including 0.9% sterile saline treatment group(sample A),mixed starter treatment group(sample B)and exogenous L-lysine and mixed starter treatment group(Sample C).Among them,the pH and TVB-N content in the sample C were the lowest.The total acid,AAN content and free amino acid content in sample C were the highest among the three samples,0.203 g/100 g,0.588 g/100 g,and 1262.57 mg/100 g,respectively.After fermentation of longsnout catfish,the organic acid content was rich and varied,which gave a better flavor to the fermented fish paste.There were no significant differences in histamine content and antioxidant activity among the three samples(P < 0.05).The content of histamine in fermented fish paste is low and the antioxidant activity is strong.The results of the electronic nose test showed that the odors of samples B and C were similar by PCA,but were different from those of sample A.In addition,the analysis of volatile flavor compounds indicated that no unpleasant flavorings were detected in the three samples.Among the three samples,Sample C showed a strong umami taste and fermented flavor with the best flavor.The results showed that the mixed starter and L-Lys could improve the flavor and nutritional value of the fish paste prepared by fermenting longsnout catfish.4.Deodorization and seasoning treatment of fermented fish pastes and cooking processIn the process of dislocation seasoning,Angel Yeast Extract can effectively deodorize the fermented fish pastes,which significantly increases the color and umami taste of the fish pastes.The best process for ripening the mushroom fish pastes by single factor and orthogonal test is to add 80 g of mushroom,100 g of fermented fish pastes,4 g of sugar,and 1.5 g of soy sauce.Under the condition of the process,the color,aroma and taste of the mushroom fish paste are all good.