| China is a large country in freshwater fishery.As the largest output freshwater breed in China,Grass carp fish(Ctenopharyngodon idellus)has enjoyed a great reputation for its large size,few muscle spines and low price among customers.However,due to the high water content and strong cathepsin activity,grass carp fish is easy to have heavier fishy smells,poorer texture,less umami taste,short storage period and so on during the storage.With the growing demands for conditioned fish products,the technology focusing on conditioning and processing freshwater fish has become one of the key scientific problems to be solved in the aquatic products processing industry.At present,the most common strategy for preparing aquatic products is combining high-concentrated salt with multiple spices aiming to the remove the fishy smell to improve the flavor and extend the shelf life of products.But meanwhile the original flavors of products are covered,and it is not conducive to public health and industrial production.At the same time,the use of quality dynamics models are rarely reported to predict the shelf life of conditioned fish products.Based on the fact that the present conditioning and processing technology of freshwater fish product can't meet the demand from consumers,the theories and methods of food chemistry,food flavor chemistry and mathematical statistics were applied in this study.First of all,the characteristics differences among Perilla extracts and their impacts on the quality of grass carp fillets were varied from each other.The optimal compositions of dipping solution for grass carp conditioning were determined by the proper variety of Perilla extract and yeast extracts,as well as the compound phosphate and salt with proper ratios.On this basis,the processing parameters of pickled grass carp were optimized,and the quality dynamic model of pickled grass carp was established to predict its shelf life.The main research contents and results were as follow:1. The suitable variety of Perilla extract for conditioning the grass carp filets was selected by comparing the characteristics of different varieties of Perilla extract and their effects on the quality of grass carp fillets.The contents of chemical components,main active components and volatile components of different varieties of Perilla extracts were determined,and the physicochemical qualities of grass carp fillets conditioned by different kinds of Perilla extracts were analyzed.The results showed that amber Perilla extracts had the highest content of solid main active components among four Perilla extracts,while the colorless Perilla extract hardly contained any solid nor other active components except polysaccharides.There were more olefins and other small molecular substances detected in the aqueous extracts of two types of Perilla leaves,leading to decrease of a~*value and the increase of b~*value of fish fillets after conditioning.Also the fish fillets turned yellow and green,and the TVB-N value grew higher,which indicated that these two Perilla leaves were not suitable for fish fillet conditioning.The colorless Perilla extract showed little effect on the color of grass carp fillets,but the hardness and chewability of the conditioned fillets were greater.The TVB-N value and TBA value of the fish slices treated with the extract of Perilla amber were kept lower.Therefore,both amber and colorless Perilla extracts can be properly used for the conditioning of grass carp slices.2. The determination of optimum proportions of each component in dipping solution by investigating the effects of the composition and the amount of the liquid on the quality of the grass carp fillets.Series of conditioning solution for grass carp slices were prepared by controlling the amounts of each material.The color,weight gaining rate,cooking loss rate and other indexes of the prepared grass carp slices were measured and sensory evaluation was carried out.The effects of each component and its amount in the maceration solution on the quality of the grass carp slices were studied and the best adding amount of each component in the maceration solution was determined,and the influence of different maceration solutions on the quality of the grass carp slices were investigated.The results showed that Perilla extract had little effect on the color of grass carp fillets,which could help to maintain the inherent flavor of fillets and weaken the fishy smell;yeast extract could reduce the cooking loss of fillets and improve the sensory score;the addition of complex phosphate could significantly strengthen the texture of fillets;the addition of salt enhanced the fresh and sweet taste of grass carp fillets.The optimum compositions of pickling were finally determined as following:Perilla extract 1.43%,yeast extract 1%,complex phosphate1%,table salt 2%,contributing to a satisfied sensory quality,the significant reduction of cooking loss rate,as well as the delaying of lipid oxidation.3. The effect of conditioning technology on the quality of the grass carp fillets was evaluated,and the optimal processing parameters about conditioning grass carp fillets were optimized.The effects of conditioning temperature,ratio of material to liquid and conditioning time on the quality of grass carp fillets were evaluated by single factor test,texture analysis,electronic nose,electronic tongue and sensory evaluation,and the optimal processing parameters for the production of grass carp fillet were optimized by orthogonal test.The results showed that within the conditioning temperature range of 0?10?,the cooking loss rate of fish fillets decreased with the increase of temperature,and the elasticity and chewability of grass carp fillets increased first then decreased,the sensory score at 4?was the highest,also the smell and taste of the three samples were distinguished obviously.The ratio of dipping material to liquid can significantly affect the smell and taste characteristics of fillets(P<0.05).When the ratio of material to liquid reached 1:5(w/v),the cooking loss rate of fillets significantly increased,which was not suitable for the conditioning of grass carp fillets.With the increase of the ratio of material to liquid,the hardness,elasticity and chewability of grass carp fillets were all tended to enhance.When the ratio of material to liquid was set between 1:2 and 1:4,the total sensory scores were higher than the others.The cooking loss rate of fillets was significantly increased when the soaking time was equal and greater than 8 h,the hardness was strengthened gradually with the prolongation of the soaking time,the elasticity and chewability was decreased to a certain extent then tended to be stable after 6 h.The optimum parameters for preparing technology of grass carp fish fillet were determined by orthogonal test as following,the temperature was 4?,the solid-liquid ratio was 1:2 and the preparing time was 6 h.4. The quality change of grass carp fillets was monitored during ice temperature storage.The dynamic model reflecting the quality change of grass carp fillets was established,and the shelf life of fillets was effectively predicted by TVB-N value model.Grass carp slices were conditioned by dipping solutions with several compositions then stored at ice-temperature.The influence of the dipping solution with different compositions on the quality of grass carp slices was assessed according to the characterizations during storage,a model for predicting the shelf life of grass carp slices was also established.The results showed that in the process of ice temperature storage,the whiteness of the slices in four groups was firstly increased and then decreased,and the p H value was firstly decreased and then increased.Also,the hardness and chewability of the fish meat decreased with the extension of time while the elasticity of slices went through a decrease then increase and the final gentle tendency.After 20 days'storage,the TVB-N value of Group B was only 13.72 mg/100g.Within the whole storage period,TBA value was increased slightly in Group B and Group D.After the kinetic analysis of the quality indexes among four groups,it was found that the purge loss of samples A and B as well as the TBA value of four groups followed the 0-order reaction,and the hardness of group A,C and D,the chewability and TVB-N value of four groups followed the 1-order chemical reaction kinetic model.By constructing TVB-N value model,the shelf life of four groups under ice temperature was predicted to be 15.13 days,18.74 days,12.58 days and 12.01 days,respectively.After verification,the relative error between the predicted value and the actual value was less thaną15%.The model can quickly and reliably predict the shelf life of grass carp fillets. |
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