The Preliminary Study Of Polyphosphates On The Quality Of Cultured Lateolabrax Japonicus

Lateolabrax japonicus is one of the common commercial fishes, and also is one of the development of aquaculture species. It has white high nutritional value and taste delicious. It is fresh to be sold, but the amounts of supermarket sales and cultured lateolabrax japonicus are increasing. The numble of chilled fresh lateolabrax japonicus is also growing. In the freezing process, water holding capacity is closely related to the quality of products. Water is a major component of food and the main factor to determine the physical and chemical properties of food and to improve food taste. Water holding capacity is one of the key factors in processing of aquatic products, In frozen storage, thawing and other processes, free water iss freezing and the protein bound water is leaving which causes frozen drip loss during thawing, then leads to nutrient loss, and bound water out of the organization can also cause the denaturation of protein and affect the quality of products. Polyphosphate is one of the most widely food quality improvers and used in meat products and aquatic products with excellent water features.In this paper, polyphosphates was investigated on improving the quality of cultured lateolabrax japonicus which was chosen as the research object. Water content of samples and the trend was studied by using the low-filed magnetic resonance. Using the peak area of T22 as an indicator, the optimal ratio of compound phosphates which had the best water holding capacity was selected and the changes of various forms of water in different treatment samples were analysed. The effects of polyphosphates on the texture, color of samples at 0℃and-18℃were based on the hardness,springiness,chewiness,adhesiveness,L,a,b. The changes of the flavor of different groups were compared by using the electronic nose and the effect of water holding capacity was determined through the general water conservation methods. The impact of polyphospahte on the structure of the samples was observd and the mechanism of polyphosphate was explored by paraffin section method and transmission-type electron microscope (TEM) method in order to provide a theoretical guide for phosphate in the processing,utilization and quality maintenance of aquatic products. The results are as follows:1. The proportions of TSPP, STPP and HMP were optimized by response surface methodology (RSM) which was based on devising single factor experiment. The concentration of sodium pyrophosphate was 1.74%, the concentration of sodium tripolyphosphate was 3.03% and the concentration of sodium hexametaphosphate was 0.92%. The order of the phosphates affecting the water-holding capacity was TSPP>STPP> HMP.Obtained the experimental factor by the response surface analysis, the value as follows:R=470120.625-6641.039*A-1618.820*B-1517.133*C-9714.985*A*B+6 528.882*A*C-1994.575*B*C-21755.325*A2-12014.298*B2-8247.6 52*C2Through the study of the impact on the discipline of moisture migration, it was known that the role of phosphate had a better reflect on the relaxation time of T22 and the integral peak area of T22. Water content was a major increase in muscle soaked in phosphate compound solution. These were consistent with the general water conservation methods.2. The effects of polyphosphates on the texture, color of samples were analyzed by using texture analyzer, color analyzer. The results showed the texture, color parameters of muscle without be soaked in phosphate compound solution had changed greatly with the increase of storage time. However, the parameters of the samples with polyphosphate changed slightly. The result that the samples treated with polyphosphate taste better by sensory evaluation was consistent with the texture result. In addition, the determination of the electronic nose was analyzed and found that the flavor of fresh samples,water immersion samples,compound phosphate samples,commercial phosphate samples were similar after cooking.3. Through the analysis of indicators, such as weight increasing yield,frozen drip loss rate,cooking loss rate,product yield,it was found the water holding capacity of the compound phosphate samples were superior to other groups. Although the yield of weight increasing is not the highest rate, it had the lowest yield of frozen drip loss. It was only 2.15% which was significantly lower than that of the fresh samples and water immersion samples and lower than that of commercial phosphate samples. The frozen drip loss rate of water immersion samples reached a maximum of 9.26%. The fresh samples was 8.36%, while compound phosphate samples was 2.19%. After one month of frozen storage, the product yield of the compound phosphate samples (91.8%) also reached the maximum value, and was higher than the other treatment groups. This confirmed the feasibility of the optimal ratio by using the low-field magnetic resonance.4. Comparing the microstructure of four treatment groups with that of four treatment groups at-18℃storage for 1 month by microscopes, we found that with the increase of storage time, cultured lateolabrax japonicus without polyphosphate had many different sizes of holes. The texture of the groups with polyphosphate had been significantly improved. The changes of tissue structure of cultured lateolabrax japonicus with and without polyphosphate were observed and compared with the fresh cultured lateolabrax japonicus. The results showed the texture of muscle tissue with polyphosphate was better and more orderly arrangement. The tissue structure of cultured lateolabrax japonicus without polyphosphate was severely damaged, protein denaturation was more serious. This results indicated phosphate can improve the tissue structure of the muscle.