Effect Of Theaflavin On Quality Characteristic Of Large Yellow Croaker During Storage

Large yellow croaker(Larimichthys crocea)is an important economic marine fish in China.In the 1970s,the resources of fish have been destroyed,and the number of wild large yellow croaker plummeted due to the fishing flooding.And it has not been effectively recovered.With the development of artificial propagation technology,large-scale cultivation of large yellow croaker has been realized.Coastal provinces such as Guangdong,Zhejiang and Fujian have vigorously developed the industrial chain of large yellow croaker in China.In 2009,total production of large yellow croaker reached 225,549tons,accounting for 13.93%of total marine fish production in China.Large yellow croaker has a tender texture,high protein content,low cholesterol cotent and is rich in inorganic salts,trace elements,essential amino acids and unsaturated fatty acids,thus,it is popular among consumers.However,Large yellow croaker is easily corrupted by several factors such as enzymatic,lipid oxidations,and microbiological activity during storage due to high moisture,protein and oil,resulting in quality reduction,and considerable economic losses.The current refrigeration technology cannot extend the shelf life of large yellow croaker,resulting in waste of resources and economic damage.As a new type of food additive,theaflavins which has good antioxidant properties,are beneficial to human health,and can be used to aquatic products preservation.In view of the above-mentioned facts,the large yellow croaker was the objective of our study.Firstly,we extracted the surface colonies of large yellow croaker frozen for 24 h and frozen for 30 d.Compared with the blank control group and Vc treatment group,we comprehensively evaluated the effect of theaflavins on the surface colony composition of large yellow croaker,aiming to explore the antibacterial effect of theaflavins.Secondly,we analyzed the effects of theaflavins on the quality characteristics,protein oxidation and lipid oxidation of large yellow croaker during refrigerated storage by sensory analysis,physical and chemical index evaluation,and oxidation index determination,aiming to analyze the fresh-keeping mechanism of theaflavins from multiple angles and provide a theoretical basis for the effect of theaflavins preservation.Then,large yellow croaker was storaged through the combination of theaflavins treatment and vacuum packaging.We analyzed the effects of theaflavins and vacuum packaging treatment on the preservation of frozen large yellow croaker in terms of freshness,protein and fat changes,aiming to provide important theoretical basis for the theaflavins preservation mechanism.Finally,theaflavins were applied to the dried large yellow croaker preservation in the market.We analyzed the effect of theaflavins on the quality characteristics of dried large yellow croaker by sensory evaluation,quality characteristic analysis and lipid change evaluation,aiming to provide a theoretical basis for theaflavins preservation mechanism of dried yellow croaker.The main results were described as following:1.Microbial composition and changes in different samples were obtained through via microbial extraction and high-throughput sequencing analysis.The results showed that,the Chao1 value,Shannon index,and Simpson index of refrigerated and frozen large yellow croaker treated with theaflavins were significantly changed compared with the blank group,indicating that theaflavin had a significant effect on the colony diversity and richness on the surface of large yellow croaker.The surface colony distribution of the large yellow croaker was changed and the growth of Acinetobacter,Myroides,Psychrobacter and Flavobacterium was inhibited by theaflavin treatment.Through LEf Se analysis,it was found that the substances from Verrucomicrobiaceae and Prevotellaceae could be synergistically with theaflavins,research and development of composite biological preservatives,and it provided a theoretical basis for the development of related composite biological preservatives.Thus,it showed that theaflavins had good antioxidant properties,had a certain effect on the composition of microbial colonies on the surface of large yellow croaker with high lipid content,could inhibit the growth of some bacteria,extended the storage time of large yellow croaker.At the same time,it provided basic reference for the development of security on large yellow croakerand compound biological preservatives.2.During the refrigerated storage,the effects of three different concentrations(0.1,0.3,0.5 g/L)of theaflavins on the quality characteristics of large yellow croaker were studied.The results showed that,he spoilage of large yellow croaker after theaflavins treatment was delayed,which was manifested in slower increase in p H,L^*value,total volatile basic nitrogen(TVB-N),carbonyls content,acid value,malondialdehyde(MAD)contents,peroxide value and the total viable counts(TVC)value,and slower decrease in the elasticity,a^*value,b^*value,Ca²⁺-ATPase activity,total sulfhydryls,reactive-sulfhydryls contents.With the increase of theaflavin concentration,the above effects became more obvious.By analyzing the amino acid composition and lipid components of each group of samples,we could find out which amino acids and fats theaflavins mainly act on.Among them,theaflavins could effectively protect the delicious amino acids,and then ensure the umami taste of yellow croaker.The protection of lipid oxidation was particularly obvious,further confirming that theaflavins had good antioxidant properties and effectively delayed the spoilage of large yellow croaker with high lipid content.3.During the frozen storage,the effects of theaflavins and different packaging forms on the quality characteristics of large yellow croaker were studied.The results showed that,compared with the blank treatment group,the protein and lipid decomposition and deterioration of frozen large yellow croaker after theaflavin soaking slowed down,which could significantly delay the quality change of frozen large yellow croaker.After vacuum treatment,the effect of theaflavins was not obvious.But,after adding ClO₂solution,the quality change of frozen large yellow croaker was significantly reduced,which was manifested in the slow decrease of Ca²⁺-ATPase activity,total sulfhydryls and reactive-sulfhydryls content,and slow increase of acid value,MDA content,peroxide value and total viable counts,improving of muscle stiffness,and unchange of elasticity.In the five groups,theaflavins and ClO₂had a significant effect on preservation.The above results further indicated that theaflavins mainly played an antioxidant role in the preservation of frozen large yellow croaker,but the antibacterial effect was not significant.4.The effects of theaflavins on the quality of dried large yellow croaker under room temperature storage and low temperature storage were studied.The results showed that,after treatment with theaflavins,the shelf life of dried yellow croaker was prolonged.Theaflavins could protect the muscle fiber structure,slow down lipid oxidations,and change the flavor composition,indicating that theaflavins could significantly improve the quality of dried yellow croaker characteristic.It not only provided a new method for dried large yellow croaker preservation,but also provided a theoretical basis for quality preservation of dried large yellow croaker.