Study On The Bacterial Community And Quality Characteristics Of Shrimp Paste Fermented By Different Processes

Shrimp paste is a traditional fermented aquatic product with a unique flavor and good nutritional value.Traditional shrimp paste is produced by natural fermentation,the microbial flora and its metabolic activities are complex,and the quality and microbial diversity of shrimp paste from different regions have certain differences.At present,the traditional shrimp paste production process generally has many problems,such as long fermentation time,high-salt content and unstable quality.In order to improve the production process of traditional shrimp paste,the quality characteristics and bacterial diversity of traditional shrimp paste sold in Huanghua were evaluated;Then,the shrimp paste was prepared by enzyme-assisted fermentation,and the quality characteristics and bacterial community evolution during the fermentation process were systematically studied;After that,a low-salt shrimp paste was prepared,and the quality characteristics,bacterial community and metabolite changes of the low-salt shrimp paste during fermentation were systematically studied;Finally,the quality,nutrition and microbiological safety of low-salt shrimp paste products were comprehensively evaluated.The main findings of this paper are as follows:(1)The quality characteristics and bacterial community of commercial shrimp paste products in Huanghua area were evaluated.High-throughput sequencing(HTS)technology and high-performance liquid chromatography were used to analyze bacterial communities and biogenic amine content,and other quality characteristics including pH,amino acid nitrogen(AAN),nitrite,and malondialdehyde were determined.The results showed that in all the shrimp paste samples,Firmicutes and Proteobacteria were the dominant phylum;Enterococcaceae,Pseudomonadaceae and Staphylococcaceae are the dominant family;The main dominant genus are Tetragenococcus,Lactobacillus and Halanaerobium.The pH,AAN,malondialdehyde,nitrite and biogenic amine content in the shrimp paste samples ranged from 6.77?8.25,0.16?0.35 g/100g,0.25?1.10 mg/kg,and 0.18?0.49 mg/kg and 18.20?469.02 mg/kg respectively.The main types of biogenic amines are tryptamine,histamine and tyramine.The correlations between Tetragenococcus and AAN,histamine and tyramine were 0.71,0.62 and 0.67(R2),respectively.The results provide a theoretical basis for improving the traditional shrimp paste fermentation process in Huanghua.(2)The changes of quality characteristics and bacterial community evolution of enzymatically assisted fermented shrimp paste were studied.The bacterial community composition of shrimp paste between different treatments was analyzed by HTS technology.The correlation between bacterial community and main quality characteristics during fermentation of shrimp paste was analyzed by Spearman.The results showed that the content of AAN and TVB-N in shrimp paste added with protease preparations increased during fermentation,which shortened the fermentation time,but it may also lead to a decline in quality.It has no obvious effect on biogenic amines after adding enzyme preparations.All shrimp paste samples obtained a total of 313864 valid sequences and 1279 OTUs.The addition of enzymes significantly affected the bacterial community composition of the shrimp paste and reduced the bacterial abundance of the shrimp paste.At the genus level,Flavobacterium was the dominant genus in the control group,and Bacillus was the dominant genus in the enzyme-added group.Bacillus increased and Paracoccus decreased after adding protease preparation.Bacillus,Flavobacteria and Paracoccus are the main differential bacteria,which affect the quality characteristics of shrimp paste.Therefore,protease preparation had an important effect on bacterial community composition,malondialdehyde,TVB-N and AAN of shrimp paste during fermentation,which laid a foundation for improving the production technology of shrimp paste with enzyme.(3)The dynamic changes of quality characteristics and bacterial community in low-salt shrimp paste during fermentation were studied.The results of the study showed that at two fermentation temperatures of 20? and 10?,the dominant phylum of low-salt shrimp paste has always been Firmicutes,Alkalibacterium and Tetragenococcus are dominant genus in shrimp paste fermented at 20? at the genus level,the dominant genus in shrimp paste fermented at 10? is Alkalibacterium and Staphylococcus.The contents of Alkalibacterium,Tetragenococcus and Rickettsia in the two groups of shrimp paste were significantly different(P<0.01).Low-temperature fermentation resulted in the increase of Alkalibacterium and the decrease of Tetragenococcus.The contents of TVB-N and biogenic amines in low-salt shrimp paste at 20? are higher than those of low-salt shrimp paste fermented at 10?,the highest content of TVB-N rose to 783.89 mg/100g in the shrimp paste fermented at 20?,which exceeds the safety limit;There was no significant difference in pH and AAN in the shrimp paste fermented at different temperatures.Therefore,the temperature had an important effect on the bacterial diversity and quality characteristics during the fermentation of low-salt shrimp paste.(4)The metabolomics of low-salt shrimp paste was analyzed.Gas chromatography-mass spectrometer(GC-MS)technology was applied to monitor metabolites during the fermentation of low-salt shrimp paste;Differential metabolites were screened out by multivariate statistical analysis,such as T-test and VIP analysis;The edclidean distance algorithm was used to analyze the correlation between the differential bacterial and the differential metabolites in the two groups of low-salt shrimp paste.The results showed that the metabolites of low-salt shrimp paste fermented under different temperature could be separated obviously by orthogonal partial least squares discriminant analysis(OPLS-DA)model.There were 44 kinds of main metabolites in the two groups of low-salt shrimp paste,including 16 kinds of amino acids,6 kinds of fatty acids,2 kinds of amines,8 kinds of organic acids,3 kinds of alcohols,3 kinds of nucleotides and 6 kinds of other compounds.30 different kinds of metabolites were obtained by using P<0.05 and VIP>1 as screening conditions,it mainly including 7 kinds of amino acids,2 kinds of esters,2 kinds of purines,8 kinds of organic acids,2 kinds of alcohols and 9 kinds of other metabolites;The levels of L-serine,L-threonine,xanthine,hypoxanthine and L-glutamine in low-temperature group(10?)were significantly higher than control group(20?),while the levels of nerazine acetate,zeaxanthin and melatonin were significantly lower(P<0.01).The correlation between Alkalibacterium and L-threonine and L-serine was 0.93 and 0.92(R2),respectively.The correlation between Tetragenococcus and methoxytryptamine,hypotaurine and L-threonine was 0.85,0.82 and-0.67(R2),respectively.(5)The quality,nutrition and microbial safety of low-salt shrimp paste were evaluated.The comprehensive evaluation of the low-salt shrimp paste with a salt content of 10%,a fermentation temperature of 10? and a fermentation time of 20 weeks was carried out with reference to the relevant standards of the shrimp paste industry.The results showed that the pH,AAN,TVB-N and total biogenic amines were 8.04,0.30 g/100g,192.46 mg/100g and 34.63 mg/kg respectively,which were all within the safe range;Escherichia coli,Vibrio Parahemolyticus,Salmonella and Staphylococcus aureus were not detected;The content of amino acids such as L-serine,L-threonine and L-glutamine is relatively high.In conclusion,the low-temperature fermented low-salt shrimp paste is a safe and nutritious shrimp paste product.In summary,the quality characteristics and bacterial communities of shrimp paste prepared by three fermentation processes were systematically studied in this paper.Tetragenococcus is the main dominant bacteria in the traditional shrimp paste of Huanghua.and its correlations with AAN,histamine and tyramine are 0.71,0.62 and 0.67(R2),respectively.The addition of neutral protease preparations would increase the content of Bacillus and TVB-N in the shrimp paste,which might affect the quality of the shrimp paste.Compared with the low-salt shrimp paste fermented at room temperature(20?),the content of Tetragenococcus,TVB-N.biogenic amine and ester compounds in the low-salt shrimp paste fermented at low temperature(10?)decreased,and the content of amino acid compounds increased.The low-salt shrimp paste fermented at low temperature is a new type of shrimp paste product with safety and good nutritional properties.These research results provide a certain theoretical basis for improving the traditional shrimp paste production process.