| Tilapia is one of the most important freshwater fish species in the world,which is nutrient-rich,and with less fish bones.Tilapia is also succulent delicious and deeply loved by domestic and foreign consumers.The tilapia industry has become an important pillar of the fishery economy in Hainan Province,of which frozen fish fillets are the most important export products.Because the ice content in frozen fillets characterize important data of moisture state and textural properties and storage properties.Studying the determination method and seeking the inner link with the physical parameters as well as grasping the frozen and the freezing process control scientific and correcting evaluation of texture features have a very important theoretical and practical significance to improve the product quality and enhance market competitiveness.In this study,we propose that the texture parameters of tilapia fillets will change in different freezing conditions,and there should be some functional relationships between them.To be through the freezing parameters and properties determination of fish,analyze the rules and characteristics,find out the relationship between fish ice content and texture parameters,then establish related model and a method for determination of content of new ice frozen fillets,and evaluate the quality of tilapia fillets,provide a reference for the development and optimization of freezing process.The results are as follows:1.Relationship and model was established between texture parameters and temperature of frozen filletsThe tilapia fillets are frozen at temperatures of-7 ?,-15 ? and-21 ?.Hardness,elasticity,gelability and chewing properties of fish fillets are measured in real time by Brookfield CT3 Determination.The results show that the variation of the texture parameters of the fillets is divided into two stages during the freezing process.The first stage is before the freezing point,there is basically no change with the temperature drop in the parameters.The second stage is in the largest generation of ice crystals with the interval,the texture parameters have decreased significantly or growth with the temperature drop,in which all of the fish hardness,stalemate and chewiness increases,and the elasticity decreases gradually with decreasing temperature.According to the law of texture parameters growth or decline with temperature,the correlation coefficients between the temperature and the texture parameters were obtained.The correlation coefficients of the fitting function were between 0.95 and 0.99,indicating that There is a good correlation between the temperature and the four texture parameters.While the elasticity and cohesiveness were slightly fluctuated,in a stable state with the temperature droping after the freezing point.2.TDR determination of ice crystal content of frozen fish filletsThe freezing of tilapia fillets was carried out at the temperatures of-7?-15? and-21 ?.First,the freezing point and freezing curves were determined,and the freezing point of tilapia was mostly between-1.80 ± 0.2 ? which was determined from the curve of conductivity change with temperature.And then the TDR was used to determine the change curve of the unfrozen water content of the fish with the temperature decreasing.According to the relationship between temperature,density and thermal expansion coefficient,make sure the density of pure water at different low temperatures.And perform function fitting with temperature T and density?water the result shows that?water ?—0.002exp(—T/8.5044)+1.003,R2=0.9996.According to the definition of water freezing rate,the relationship between the volume water conten?0??,the density?0water??0water and the volumeV0fish?Vfish of the fish in different freezing conditions was analyzed,the parameters were integrated and calculated according to the principle of conservation of water quality in the process of freezing.The equation is used to obtain a new method for the determination of ice crystals in tilapia.The formula is:?=1-?0water Vfish ?/?0 waterV0fish?03.Establishment of texture parameters associated with the ice content modelThe hardness,elasticity,stalemate and chewiness parameters of the fish were measured in real time by the Brookfield CT3 model at-7 ?,-15 ? and-21?,and the TDR was measured at the corresponding temperature of the ice crystal content and texture parameters were modeled.The results showed that the hardness,stalemate and chewing property of the fish were all related to the content of ice crystals as a whole.The correlation between stalemate and ice content was relatively good among them.The average correlation coefficients were 0.9920.According to the size of the correlation coefficients,it is shown that the correlation between the texture parameters and the ice crystal content is different in different freezing conditions.In the case of slow freezing,the correlation coefficient of chewiness is less,whose value is 0.9897,the the correlation coefficient of hardness is the best,whose value reach up to 0.9917;and in the quick freezing,the value of the correlation coefficient of chewiness was 0.9902,and the value of the correlation coefficient of stalemate was 0.9935.4.Comparative analysis of ice crystal correlation modelAccording to the current reported in the determination of ice content in food,the mainly method is Hsieh formula method,which compares with the results of the above study at-4?,-7?,-18?,21? and-24? freezing conditions.The results showed that the texture parameter correlation method and the TDR method were correlated with the Hsieh formula when the fish fillets reached their respective freezing end points.And the ice crystal content of fish samples were calculated and carried analysis of variance by different calculation methodsin different frozen states.The difference between the values is small,which proves that the correlation model of this study has high reliability.5.Study on the relationship between ice crystal content and texture qualityThe fish fillets were frozen at different low temperature conditions for 30 days,60 days and 90 days.It could obtained the ice content of fish fillets were 64.93%,71.03%,89.24%,92.46%and 94.85%which calculated by association model of stalemate whose correlation is the best with ice content in the establishment of the texture parameter and the ice crystal content in the fitting function.And the fish fillets were tested by CT3 Texture instrument after thawing.Whose data was compared with the fresh fish.According to the difference between them to determine the effect of ice content on the texture quality of frozen fish.The results showed that in the same freezing time,the hardness,elasticity,cohesiveness stalemate and chewiness of the fish fillets were more similar to fresh fish fillets when the ice content is 89.24%.When the ice content is 92.46%,the elasticity of the fish fillets is the best.In addition to,it was found that ice content of 92.46%and 89.24%of the texture parameters are closer,both of them were superior to others.It can be found that the effect of ice crystal content on fish quality is significant,which provides the theoretical basis for the optimization of fillet freezing process. |
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