Formation Mechanism Of Dominant Spoilage Bacteria In Iced Fish And Competitive Inhibition Of Probiotic

Marine fish is popular with people for its nutritional value and delicious taste,but it mainly sold as iced fish which make it easily to be spoiled.Therefore,it is imperative to reveal the spoilage process of iced fish.In this study,adhesion ability of spoilage bacteria was provided as a new direction to clarify the reason why Shewanella and Pseudomonas become the dominant spoilage bacteria during storage.At the same time,the adhesion ability of probiotics against spoilage bacteria were also investigated.Finally,the adhesion and growth of spoilage bacteria in the intestine of fish,the effects of probiotics on spoilage bacteria and gut microflora were studied in vivo.The main contents and results were as follows:1.Adhesion properties of spoilage bacteria were identified by surface hydrophobicity,auto-aggregation ability,adhesion ability and ability of biofilm formation.Shewanella was significantly stronger than Pseudomonas,which made it have dominant in the spoilage process of fish.Meanwhile,time,temperature,pH,salt concentration and other factors significantly affected properties of adhesion and biofilm.The total number of bacteria,TVB-N,TMA,K value,siderophore and protease activity were used to evaluate the spoilage ability of spoilage bacteria.The results showed that Shewanella was superior to Pseudomonas.The correlaspoilage tion analysis indicated that there was a positive correlation between spoilage ability and adhesion properties of spoilage bacteria.Specifically,the adhesion ability of bacteria to intestinal mucus had the most significant positive correlation with spoilage ability,which indicated that the high adhesion ability of spoilage bacteria to fish mucus was the reason for it to be the dominant spoilage bacteria.2.The same methods were used to evaluate the adhesion properties of probiotics,the results showed that the ability of Bacillus subtilis BS08 and Bacillus megaterium BM01 were similar,and there were similarities between Bacillus spp.As for adhesion antagonism of probiotics,different probiotics inhibited the adhesion of spoilage bacteria to mucus in different antagonistic ways.BS08 mainly inhibited Shewanella to intestinal mucus by competitive adhesion,and replacement adhesion for Pseudomonas;as for gill and intestinal mucus,exclusion adhesion is the main way.Bacillus subtilis BS08 was selected for the third part after analysis.3.Bacillus subtilis BS08,two Shewanella and two Pseudomonas were used to discuss the adhesion of bacteria in the intestine of fish and changes of gut microflora in vivo.The results showed that adhesion ability of spoilage bacteria in fish intestine was stronger than that of BS08.Shewanella rapidly proliferated in the early stage,while Pseudomonas increased significantly during the latter period of storage.BS08 had no advantage in adhesion,but it could significantly inhibit adhesion and growth of Shewanella and Pseudomonas in the intestine.BS08 could regulate the abundance and diversity of gut microbiota,regulate the total proportion of dominant phyla and bacteria composition structure during storage.Besides,TVB-N remained stable and the change was totally small.But it was also found that Shewanella was slightly stronger than Pseudomonas in spoilage.Bacillus subtilis BS08 could reduce TVB-N by inhibiting the growth of spoilage bacteria,which delayed the degree of spoilage in fish during storage.In summary,the study demonstrated in vitro and in vivo that strong adhesion ability of spoilage bacteria to fish was the important reason why it to be the dominant spoilage bacteria.Bacillus subtilis BS08 could inhibit the colonization of spoilage bacteria by adhesion antagonism,regulate the abundance?diversity and community difference of gut microbiota,thereby delaying the spoilage process.The study provides the foundation for the development of preservatives from probiotics.