| Tilapia is one of the important commercial fishes in China. It is well received by large number of consumers and farmers because of short growth cycle, adaptable and resourceful, quality meat and rich nutritious. Our country has formed the main aquaculture production and export processing base in Hainan, Guangdong, Fujian and Guangxi Province. At present, the main form of Tilapia processing trade industry is frozen fillets. During the processing and storage. The fillets’nature will be changed to some extent influenced by quality of materials, technology, storage conditions and other factors. People need convenient and effective evaluation methods to detect the quality of frozen Tilapia fillets, enrich its quality evaluation system, and provide the basis for improving the level of processing technology and quality.This subject carried on the research of quality evaluation methods of Tilapia. Tested the frozen Tilapia fillets’physical property parameters, such as water activity, color and texture properties. Using the content of the fractal dimension to explore the spatial arrangement of frozen Tilapia tissue in different storage temperature and period. Hope that through the establishment of mathematical model of fractal dimension of node rational characteristics will find out a method for evaluating the quality of frozen Tilapia fillets based on fractal dimension.1. Change of physical property parameters of fillets in different storage conditionsPhysical property parameters of Tilapia fillets were determined under -4℃、-7℃、-21℃ and -40℃ including water activity, color and texture parameters. The results show that the fish water activity in the four kinds of storage temperatures decreased with prolonged storage time gradually, and the time effect on fish water activity significantly (P<0.01). Texture parameters were determined such as hardness, springiness, cohesiveness, chewiness and resilience. The index of hardness, elasticity and chewiness decreased with times at different storage temperatures showed significant differences, indicating the storage time keep significantly influences on these parameters.2. Changes of color quality offish slices under different storage conditionsL value, a* value, b* value and A E*ab value in color determination decreased in different degree, and a* value decreased more obviously from 7.12 to-1.38 in-4℃. Meanwhile, chromatic aberration Δ E*ab value calculated also showed significant differences. It concluded that the storage time had a significant effect on a* value and Δ E*ab value (P<0.01).3. Fractal features of frozen Tilapia tissuesFractal dimension can characterize complex random shape and phenomenon. Experimental samples were processed into frozen section, and the microscopic images were observed and obtained by BX51 Olympus microscope 20×objective lens. We can characterize space arrangement of fish issue because it was in accord with fractal features. Fractal dimensions (box dimension) were calculated through Matlab 7.0 software, concluding that fractal dimension decreased with storage time. Fractal dimension decreased from 1.9546±7.1024E-4 to 1.8787±3.5119E-4 in-4℃ distinctly, and storage time had a significant influence on it.4. Model fitting combining fractal dimension and physical property parametersFractal dimension can characterize arrangement of fish issues, physical property parameters were changed with the variation of issues. Experiment aimed at researching the relation among fractal dimension and physical property parameters, and fitting mathematical function models. These models were fitted according to previous experimental results with the correlation coefficient higher than 0.9. Therefore it can be used as methods for predicting the change rule of the physical property parameters and judging the quality of fish, through calculating fractal dimension and comparing with fresh fish.In conclusion, frozen Tilapia fillets quality depends on the spatial structure and surface characteristics of the fish tissues, and it’s closely related to the processing methods. The fractal images and dimensions can be used to quantitatively evaluate the change trend of spatial structure and surface characteristics in different storage conditions, fractal dimension is a new evaluation methods of fish quality which providing for a new way of product process improvement and quality prediction of Tilapia fillets.. |
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