Quality Characteristics And Shelf Life Of Large Yellow Croaker In Aquaculture And Storage

Large yellow croaker（Larimichthys crocea）has the characteristics of delicate meat,golden scales,delicious taste and rich nutrition.It is an important economic fish in China.In the mid-1980s,the artificial breeding technology of large yellow croakers was broken,and the aquaculture production increased year by year.In 2017,it reached more than 170,000 tons.The breeding mode is mainly based on traditional small-scale cage culture.It has the characteristics of small investment and easy management,but there are problems such as obesity of fish body,deterioration of body color,soft flesh and easy disease.In the production practice,how to achieve healthy breeding and sustainable development of large yellow croaker,to achieve quality priority and improve quality and efficiency,the development of new farming mode has gradually become one of the hot spots in the industry.In order to explore the differences in nutritional quality of large yellow croaker under different new culture modes and the effects of different stages（seasons）on the nutritional quality of large yellow croaker under different new culture modes,how to preserve fresh fish and shelf life of high quality large yellow croaker It is necessary to study the nutritional indicators of large yellow croaker under the new culturing mode,including three items:1.Study on the Quality Difference of large yellow croaker under Wild and Four Cultivation ModesIn order to understand the quality characteristics of large yellow croaker under different culture modes,the wild large yellow croaker was used as a reference,and five existing culture modes of large yellow croaker（deep-water cages G1,seine G2,multi-connected frame cages G3 and small raft cages G4）were comparatively analyzed for morphology,color,crude nutrients,fatty acids and amino acids.The results showed that except for G1,the condition factor of wild fish was lower than that of cultured fish,except G4,there was no significant difference between wild and cultured fish（P>0.05）;wild fish body length-height ratio was higher than cultured fish.As for the skin color,the wild fish had the highest L*value,the a*value was the lowest,and the b*value was lower than G1 and G2.The crude fat of wild fish was smaller than that of cultured fish,and the crude protein content was larger than that of cultured fish.The amounts of fatty acids of both wild and cultured large yellow croaker were found in the following decreasing order:Σsaturated fatty acids（SFA）>Σmonounsaturated fatty acids（MUFA）>Σpolyunsaturated fatty acids（PUFA）.The SFA andΣMUFA of wild fish were higher than the cultured fish,while theΣPUFA was lower than the cultured fish;besides,the amount of C20:5（EPA）and C22:6（DHA）in wild fish were lower than those of cultured fish,the difference was significant（P<0.05）,theΣ（EPA+DHA）values of wild fish were smaller than those of cultured fishΣ（EPA+DHA）.The contents of TAA,NEAA,SEAA and EAA in wild fish were significant higher than those in cultured fish（P<0.05）.Wild fish EAA/TAA,EAA/NEAA are larger than cultured fish（except G4）;wild fish NEAA/TAA was smaller than cultured fish（except G4）.The results showed that compared with wild large yellow croaker,the cultured large yellow croaker had differences in growth characteristics,body skin color and muscle color,and basic nutrients.However,from the perspective of food fish nutrition,the cultured large yellow croaker has some indicators such as condition factor.There was no significant difference between cultured（deep-water cages and seine）and wild large yellow croaker in body color,crude protein and polyunsaturated fatty acid,moreover,even higher than that of wild fish.However,the deep-water cages and seine culture models can significantly reduce fish condition factor and crude fat content which promote the quality of cultured large yellow croakers,and it had a certain guiding effect on improving the quality of large yellow croaker and optimizing the culturing mode.2.Effects of culture models and stages on the nutritional quality of large yellow croakerTo evaluate the morphology,color and nutritional composition of large yellow croaker（Larimichthys crocea）,cultured fish from three culture models（seine-S,deep-water cages-D,raft cages-R）at the initial（summer）,third（autumn）and sixth（winter）（0,1,and 2,respectively）cultured month were compared to wild fish（W）;the condition factor（CF）,color,proximate composition,fatty acids and amino acids were observed.The results showed that the wild large yellow croaker had lower CF than the cultured fish,and the length-height ratio（LHR）was greater than that of the cultured fish.Regarding the skin color,the lightness（L*）value of wild fish was greater than that of cultured fish;the redness（a*）value was lower than that of cultured fish,and the yellowness（b*）value was greater than that of cultured fish（except for S1,G2,and G1）.Wild fish moisture content（excluding D1）and ash content（excluding R0）were lower than those of cultured fish;the crude fat content was significantly lower than that of cultured fish（P<0.05）（excluding G2）.The crude protein content of wild fish was significantly greater than that of cultured fish（P<0.05）.The amounts of fatty acids of both wild and cultured large yellow croaker were found in the following decreasing order:Σsaturated fatty acids（SFA）>Σmonounsaturated fatty acids（MUFA）>Σpolyunsaturated fatty acids（PUFA）.TheΣSFA andΣMUFA of wild fish were higher than those of cultured fish.TheΣPUFA of wild fish was significantly lower than that of cultured fish（P<0.05）.Total amino acids（TAA）,non-essential amino acids（NEAA） and essential amino acids（EAA）of wild fish were higher than those of cultured fish（excluding R1）.The TAA,EAA,semi-essential amino acids（SEAA）and NEAA of cultured fish showed a rising trend first and then decreased.The EAA/TAA and NEAA/TAA of wild fish were lower than those of cultured fish.It was concluded that the morphology,color,proximate composition,fatty acids and amino acids of seine and deep-water cage phased imitation eco-cultured fish at the sixth month were significantly greater than those of R model fish;the integral quality of large yellow croaker was improved remarkably.3.Effect of sodium alginate film preservation on the quality of ice-temperature large yellow croakerUsing iced fish as a control,the effects of sodium alginate on the storage quality and shelf life of large yellow croaker stored at ice temperature（-1°C）were studied,and coated with 0%,1.0%,1.5%and 2.0%sodium alginate,respectively.Large yellow croaker,vacuum packed in-1°C incubator,to determine the total number of colonies,H₂S bacteria,pH,TVBN,TBA,sensory evaluation,color difference and texture,etc.The effect on the shelf life of ice-temperature large yellow croaker was studied.The results showed that the 1.0%,1.5%and 2.0%sodium alginate treatment groups reached the sensory rejection end on the 23rd,27th and 25th day respectively,and the sensory scores of color,flavor and muscle tissue were all less than 2 points;The b*value of large yellow croaker in the 1.5%sodium alginate treatment group still increased in the final stage of storage,and the△E value also increased significantly.The cohesiveness,springiness and chewiness of 1.5%sodium alginate coated large yellow croaker were Significantly elevated on day 27（P<0.05）;as for TVBN,1.0%,1.5%,and 2.0%preservative concentrations of large yellow croakers reached 32.8,30.4,and 33.0 on days 25,29,and 27,respectively,reaching shelf life End point;TVC and H₂S bacteria in the 1.0%,1.5%and 2.0%preservative treatment group of large yellow croaker reached the limit on the 25th,29th and 27th day respectively;in summary,the changes of TVBN TBA,TVC and H₂S-producing bacteria of 1.5%sodium alginate concentration fish were slower than the changes of 1.0%and 2.0%,the antibacterial effect was better,the lipid oxidation was slowed down,and the shelf life was effectively extended to 29 days.