Study On The Processing Technology Of Prepared Grasscarp Fillets And Changes Of Quality During Storage

Demand for prepared aquatic products has been increasing dramatically in China, due to the significant improvement of people’s living quality and the development of cold chain logistics system.The objective of this study is to optimize packaging method and investigate quality changes of products during storage. Influences of soaking ingredients, package method and storage temperature on physicochemical properties, flavor and bacteria flora of vacuum-soaked grass carp fillets were studied. Results are shown as below.1. Effects of salt and polyphosphates on the quality of grass carp fillets during conditioning process were studied. Water holding capacity, textural properties and sensory quality of the vacuum-soaked grass carp fillets were significantly improved by addition of 2% salt and phosphate solutions within a certain concentration. Besides, the mixed phosphate was proved to be better than single phosphate on improving fillet quality. The optimum conditions for obtaining the highest water holding capacity, textural properties and sensory quality were determined to be 2% phosphates(sodium tripolyphosphate : sodium pyrophosphate : trisodium phosphate : sodium hexametaphosphate = 2:2:2:1) and salt, soaking with solution(1:1.15) under vacuum(70 cm Hg) for 30 min.2. The effects of packaging methods and storage on physicochemical properties of grass carp fillets were investigated. With the extension of storage time, aerobic bacterial count, K value, total volatile basic nitrogen(TVB-N) value and 2-thiobarbituric acid(TBA) value increased for all five different processing method(A-fresh fish slices vacuum packaged and stored at 4℃, B- fresh fish slices with MAP stored at 4℃, C-fresh fish slices vacuum packaged and stored at-1℃, D- fresh fish slices with MAP stored at-1℃, E-prepared fish slices with MAP stored at-1℃). Compared with the cold storage(4℃), the microorganism increased slower and quality of fresh grass carp fillets deteriorated slower under ice-temperature(-1 ℃). When stored at 4 ℃, modified atmosphere packaging(MAP) and vacuum package had no significant difference on slices quality. Under ice-temperature(-1℃), the shelf life was longer and quality of fresh grass carp fillets better for MAP than vacuum packing. Overall, the quality of grass carp fillets treated with phosphate was superior to other that with other treatments during the storage.3. The effects of package methods and storage temperature on volatile characteristics of grass carp fillets were studied. With the prolongation of storage time, the fish flavor declined gradually. The volatile of the grass carp fillets showed obvious difference among five different kinds of processing methods. Response values of electronic nose sensor showed good correlation between the physical and chemical indicators. Combined with the electronic nose sensor response values and the measured physical and chemical values, a quantitative prediction model for the value of TVB-N and the total number of colonies of grass carp slices which was based on electronic nose by using the BP neural network was built. The prediction accuracy of the TVB-N value in five samples were 98.08%、95.72%、98.60%、98.99%、98.29%, respectively, and for the total number of colonies were 98.04%、98.97%、98.74%、98.75%、97.75%, respectivly.4. Effects of package methods and storage temperature on the microbial growth was investigated. The microbial growth of the grass carp fillets showed obvious difference among five different kinds of processing methods. PCR-DGGE results showed that there were few microorganism number in fresh fish fillets. With the extension of storage time bands in PCR-DGGE gel increased rapidly. The color of same bands got darker, which belonged to the dominate microbial. During the last storage period, some bands got darker while some bands got lighter, which implied that the dominate microbial grown rapidly, while number of some microbial declined.