Research On Quality Characteristic Of Frozen Tilapia Fillets Based On Correlation Of Physical Properties

Tilapia is one of important economic fish in Hainan Province in recent years. With rapid development, its main products are frozen tilapia fillet. Preparation of frozen tilapia fillets frozen, in this process, the phase change into ice water, fish of the physicochemical properties, including physical and chemical indicators, texture index and microcosmic structure arrangement will have greatly changed. The paper was based on the changes of physicochemical properties in the process of food preservation at low temperature, and application and reference about different parameters of freeze tilapia fish quality were evaluated, including:1. Physicochemical parameters:Physicochemical properties of tilapia were often associated with moisture, organic matter and other components of tilapia tissues on different condition.In the present study, the most common method to evaluate the quality of frozen tilapia fillets were sensory evaluation method and chemical method, which are based on the sensory quality or certain chemical substances fish residue (usually volatile basic nitrogen residue) instant quality evaluation of tilapia fish. In the process of cryopreservation, this two index values with increasing storage time are all linear variation. In the store, when the temperature is lower, the variation of magnitude is smaller.In our research, the evaluation of frozen tilapia fillet quality index is extended to tilapia pH value, conductivity, water activity. Among them, the variation of pH value is the first decline after increasing trend; electrical conductivity and water activity is a linear decreasing, whose trend are similar to the change of sensory evaluation and chemical parameters. Through calculating the correlation between these indexes and two indexes, we can draw the conclusion, conductivity and water activity also relatively good quality of tilapia instant reaction.2. Texture parameters:Tilapia textural properties always depend on the composition and arrangement of the body tissues.In our experiment, the main quality relates to the structure index including hardness, elastic and cohesion. Among them, the hardness change is not the rule and unable to draw a more reasonable fitting curve; elastic and cohesion have linear decreasing trend, when temperature was lower, the variation of magnitude was smaller.The correlation between texture parameters with conventional quality parameters was evaluated. Experimental results show that the curves of, the Pearson correlation between frozen tilapia fillet elasticity and conductivity, water activity, volatile basic nitrogen content, sensory score, with temperature-5℃, were-0.975,0.982,-0.973,0.974;-0.966,0.961respectively,-0.983,0.989,at-20℃; and-0.979,0.972,-0.970,0.976, at-40℃,which are significant correlations.The kinetic equation of changes of the elastic in process of tilapia fish frozen was calculated. The of activation energy Ea was89.866kJ/mol, and the pre exponential factor ko=1620.68. On the basis of the result, Arrhenius equation of vacuum packaging tilapia fish fillets during storage between rate constant k and storage temperature change t is: k=1620.68exp (-89866/RT).With above results, the predict of the shelf life of frozen tilapia fillet is made, the results were compare by the measured data, in the temperature10℃,5℃,0℃,-5℃,-10℃, the experimental errors are15.61%,-8.69%,-2.65%,-6.34%,-3.33%, are within acceptable limits respectively.Ibid, at-5℃, correlation of frozen tilapia fillet cohesion changes were-0.986,0.984,-0.983,0.988;-0.986,0.980respectively, and-0.970,0.979,-0.992at-20℃,-0.974,0.9860.985at-40℃. Activation energy Ea=53.532kJ/mol and pre exponential factor ko=215.64. Arrhenius equation is k=215.64exp (-53532/RT). Prediction of frozen tilapia fillet quality guarantee period, the experimental error at the temperature of10℃,5℃,0℃,-5℃,-10℃were-0.60%,-8.91%,3.08%,2.64%,5.52%,respectively.Therefore, real time quality can be evaluated by elastic and cohesive properties of frozen tilapia fillets, as well as the prediction of frozen tilapia shelf life.3. Fractal dimension of optical sections:This is one of the most innovative parts in our research. In our experiment, fractal dimension concept was introduced to characterize the microstructure distribution characteristics of frozen tilapia fillets. The frozen tilapia fillets, uptake of optical microscopic image, computing fractal dimension to characterize the material arrangement, by fitting the change regularity of different freezing conditions the fractal dimension, the quality characteristics of frozen tilapia fillets.Frozen tilapia fillet optical microscopic image quality assessment method based on fractal dimension. In-5℃, the correlation between fractal dimension and conductivity, water activity, volatile basic nitrogen content, sensory score changes were-0.986,0.985,-0.983,0.985; respectively, and-0.991,0.988-0.984,0.963at-10℃,0.985;-0.987,-0.990,0.982at-15℃. Activation energy Ea was28.724kJ/mol and the pre exponential factor ko=20.803, Arrhenius equation is:k=20.803exp (-28724/RT). The prediction of frozen tilapia fillet quality and shelf life, the experimental error were-7.00%,-3.36%,-5.28%,-8.16%,3.14%,2.27%at the temperature of10℃,5℃,0℃,-5℃,-10℃,-15 ℃. The final results show that:the calculated fractal dimension of the frozen tilapia fillet optical microscopic image can evaluate frozen tilapia fillets instant quality change, the forecast of shelf life, which has a certain guiding significance and application prospects in the frozen study.To sum up, measuring the experimental system of the frozen tilapia fillet quality parameters changes in different preservation condition, these parameters were analyzed, the great expansion of tilapia fish quality evaluation method, established a comprehensive system for related research.