Effect Of Lactobacillus Sporpgenus On Quality Of Cultured Large Yellow Croaker(Pseudosciaena Crocea) Fillets During Storage

The large yellow crockar(Pseudosciaena crocea), one of the main maricultured fish, is widely marketed in China and abroad. However, due to the high activities of proteases and high content of the proteins, fish is liable to suffer spoilage and protein degradation during the storage time, eventually leading to the decline of its freshness and reduce the acceptance of the flesh for human consumption and cause a huge lose to the economic. So it was essential to inhibit the spoilage bacteria based on promise of the large yellow croaker quality and to extend the shelf life.In view of the facts, the probiotic Lactobacillus sporpgenus was studied to use as the biopreservation. First of all, the extracellular product produced by the probiotic, Lactobacillus sporpgenus, was to evaluate the degrees of antimicrobial activities on the main spoilage of the aquatic product. Secondly, sensory, physicochemical and PCR-DGGE technology were all used to evaluate large yellow croaker quality over a period of20days. Finally, the effect of probiotic, Lactobacillus sporpgenus, on biochemical and functional characteristics of muscle protein from large yellow croaker were studied based on the denaturation and degradation of protein. Our results were described as following:1. The result indicated that the extracellular products produced by Lactobacillus sporpgenus showed different degrees of antimicrobial activities on the E. coli, P. aeruginosa and Shewanella spp. Moreover, the extracellular products showed relative stability at different high temperature. However, higher antimicrobial activity was found at acidic and neutral pH value,while its activity decreased significantly when treated with pH higher than8or lower than2(P<0.05). The extracellular product kept above88%antimicrobial activity when treated with catalase, while its activity was reduced to about50%when treated with protease K and trypsin. Meanwhile, the result showed the maximal antimicrobial activity was observed after48h when incubated at37℃and pH6.0.2. A solution of Lactobacillus sporpgenus at three final concentrations:T-1,1×108cfu/ml; T-2,1×107cfu/ml and T-3,1×106cfu/ml were used to dip in the large yellow croaker and quality changes of the large yellow croaker were observed. Compared with the control groups, the results showed that the treated groups kept at the relative lower pH and TBA values, but were not significant difference with the control group during the storage (P>0.05). The TVB-N of the treated groups were significantly lower than the control during the storage at4℃(P<0.05), while the difference between treated groups were not significant before12days of the early at storage (P>0.05).The K value of the treated groups were also significantly lower than the control (P<0.05), while it was not significant during the storage at4℃between the treated groups (P>0.05). The result obtained in our study showed that the probiotic Lactobacillus sporpgenus could more effectively maintain the good quality of the large yellow croaker and the optimal concentration was1×107cfu/ml, about4days could be extended during the storage.3. PCR-DGGE technology had been built to analyze the diversity of bacterial in large yellow croaker during the storage. Then22species of bacteria were detected in the large yellow croaker. PCR-DGGE analysis can efficiently characterize the bacterial community in large yellow croaker and monitor the variation in major spoilage bacteria for seafood preservation.The bacteria community in large yellow croaker was complex, above50%of all the spoilage were Shewanella. Other species such as Photobacterium, Aliivibrio, Vibrio, Pseudomonas, Proteobacterium and Aeromonas were also detected as minor organisms in large yellow croaker. The results of the PCR-DGGE also showed that Lactobacillus sporpgenus could surpress the growth of the predominant spoilage organisms inculding part of Shewanella, Pseudomonas, Aeromonas and Vibrio.sp, but could not compeletely control the growth of Shewanella bacteria, Photobacterium, Proteobacterium and Alivibrio logei during the storage. 4. The changes of biochemical characteristics and tissue microstructure of large yellow croaker were studied by thiobarbituric (TPA), color, salt solubilities, Ca2+-ATPase activities, sulfhydryl contents, surface hydrophobicity, SDS-PAGE analysis and muscle microstructure from large yellow croaker treated with different concentration of Lactobacillus sporpgenus during ice-temperature storage. The results showed that the color of the treated groups were not significant difference with the control group (P>0.05); The difference of TPA between control and treated groups was significant (P<0.05), it was significant between T-2with T-1and T-3(P<0.05), while T-1and T-3was not significant (P>0.05); Lactobacillus sporpgenus could effectively slow down the decrement of Salt solubilities, sulfhydryl contents, Ca2+-ATPase activities and the increment of surface hydrophobicity of myofibrillar protein (P<0.05). The result of SDS-PAGE showed that treated groups could slow down the decrease of MHC. At the same, the pictures of muscle microstructure were showed the fiber area was decrease and the gaping area was increase significantly. So the probiotic Lactobacillus sporpgenus could protect protein degradation of large yellow croaker and the best concentration was about1×107cfu/ml.