Preservation Technology Of Ozone Pretreatment Of Large Yellow Croaker And Antibiotic Resistance Of Fish Associated Bacteria

Large yellow croaker(Pseudosciaena crocea)is a species of marine cage-cultured fish with the largest production amount in our country.Due to its high nutrition vale and delicious taste,it is deeply welcomed by consumers.Ice-fresh and micro-frozen aquaculture products have become current consumption trends.But a series of physiological and biochemical reactions and the growth of microorganisms after the death of fish,could severely affect its storage quality and edible value.In view of this,based on the existing preservation methods,to develop a kind of better physical preservation method for large yellow croaker is very important.In addition,antibiotic resistance has become a major public health concern.As for the fact of the spread of antibiotic resistance in aquaculture products,it is essential to study the antibiotic resistance of isolates from large yellow croaker.Therefore,this study investigated the effect of the ozone pretreatment,using different concentration combined with atmosphere packaging method,on the storage quality of cultured large yellow croaker under both ice-fresh and micro-frozen conditions.The sensory quality,microbiological indexes,physical and chemical indexes were measured during the storage process,in order to obtain the best storage conditions for ice-fresh and micro-frozen large yellow croaker,respectively.Also the antibiotic resistance of isolates from large yellow croaker were investigated.Results of this study could provide scientific basis for the supply of safe and nutritional aquaculture products including large yellow croaker.The research content and results are as follows:1.Optimal concentration of ozone pretreatment for large yellow croaker stored at low temperature.Large yellow croaker samples were stored at(-1.0±0.5)℃(ice-fresh temperature)and(-3.0±0.5)℃(micro-frozen temperature),respectively.The effects of the ozone pretreatment,using different concentration(low:1.03mg/L,medium:3.12mg/L and high:5.01mg/L)combined with atmosphere packaging method(75%CO2+25%N2),on the storage quality were investigated.During the storage,sensory score,water loss rate,pH value,TVB-N content,TBA value,K value,protein content,texture and total bacteria number of large yellow croaker samples were measured.Results showed that compared with control group without ozone pretreatment,no matter at ice-fresh or micro-frozen temperature,the indicators of the ozone pretreatment groups including total number of bacteria,water loss rate,pH value,TVB-N content,TBA value and K value showed slower increasing trends,while sensory score,protein content,hardness and chewiness showed slower decline trends.As the increase of the ozone concentration,the preservation effects were better.Therefore,within the ozone concentration range tested in this study,the ozone pretreatment using high concentration(5.01mg/L)combined with atmosphere packaging(75%CO2+25%N2)could be the optimal fresh-keeping way for large yellow croaker at low temperature,which could ensure its good storage quality.2.The antibiotic resistance of bacteria from large yellow croaker.Phenotypic resistant population against sulfamethoxazole with trimethoprim(Sul/Tri),tetracycline(Tet),chloramphenicol(Chl),ciprofloxacin(Cip),cefotaxime(Ctx)or streptomycin(Str)were screened by conventional plating with the corresponding antibiotics.Results showed that about 102～103CFU/g of various antibiotic resistant(ART)bacteria were prevalent in all fish samples examined,including fish intestine and surface rinsing water.Results of disc diffusion tests showed that majority of isolates were multidrug resistant and exerted the resistance to several antibiotics including Sul/Tri,Tet,Chl,Ctx,Str,Cip,ampicillin,vancomycin,furazolidone,norfloxacin and enrofloxacin to different extent.The MIC assessment results showed that 57.1%Sul/Tri resistant bacteria had MIC value of 608/32μg/mL,19.0%Tet resistant bacteria had MIC value of 64μg/mL.And eight genera of bacteria were identified by 16S rDNA sequencing,including Shewanella sp.,Pseudomonas sp.,Stenotrophomonas sp.,Alcaligenes sp.,Morganella sp.,Proteus sp.,Carnobacterium sp.and Aeromonas sp..Using conventional PCR,Tet resistance genes including tet C and tet D were detected in the isolates,and the gene carriers were indentified as Stenotrophomonas sp.(tet C)and Shewanella sp.(tetD).