Study On Controlled Freezing-point Storage And Modified Atmosphere Packaging Applied To The Preservation Of Fresh Grass Carp Slices

With the development of the supermarkets,fresh aquatic products in small packages gradually become an important sale mode such as fish slice,fish steak and so on.But the aquatic products are insufficient on market because of unsuitable preservation technology. Based on studies of the basic chemical composition and effects of addition on the thermal properties of fresh grass carp slices,effects of changes for number of microorganism and reducing treatment on number of microorganism during processing,and changes of qualities during different storage temperatures and gas proportion were researched to establish quality change and bacteria growth kinetics models of fresh grass carp slices and to determine technical parameters of Controlled Freezing-point Storage combined with Modified Atmosphere Packaging.Results were summarized as follows:1.The content of water,water-solubility,protein,fat and ash in fresh grass carp was 77.55%,5.93%,17.93%,3.27%and 1.26%,respectively.The freezing point,the freezing temperature and enthalphy of muscle were -0.66℃,-10.76℃,209.1 J/g,respectively. With adding amount of salt and sucrose increased,the freezing temperature,freezing point and enthalphy would decrease.The relationship between freezing point and adding amount of salt and sucrose can be well described by the regression equation,T_f= -0.81-87.62X_N-13.70X_S.The freezing point of fresh grass carp slices muscle decreased to -3.52℃when added 3%salt and 0.6%sucrose.2.The critical control points of reducing re-pollution were slicing and immersing procedures during processing.We studied bacteria number reducing treatment with four solutions such as citric acid,latic acid,chlorine dioxide and peroxyacetic acid.The optimum treatment was immersing the slices in 3%citric acid solution at 20℃for 10 min,and the aerobic bacterial counts reduced by 96.9%after the treatment.3.The storage temperatures had significant effects on qualities and shelf life of fresh grass carp slices.K value,water holding capacity,rigidity and sensory quality of fresh grass carp slices stored at different temperatures decreased with storage time,while aerobic bacterial counts,total volatile basic nitrogen(TVB-N) value,2-thiobarbituric acid(TBA) value and drop loss rate increased.The growth of microorganism and quality of slices were slowdown at -0.7℃.In terms of describing changes of aerobic bacterial counts of fresh grass carp slices stored at different temperatures,modified Gompertz model was better than the first order kinetics model and Logistic model.The storage temperatures had significant effects on maximum specific growth rate and lag time of microorganism,whereas no significance on maximum quantity of microorganism. Changes of TVB-N value and TBA value with storage time increased were consistent to the first order kinetics model.The growth rate constant of TVB-N and TBA value increased with storage temperature added.According to aerobic bacterial counts,the predictive shelf life at 15℃,10℃,5.0℃and -0.7℃were 1.0d,1.9d,4.6d and 17.5d, respectively.4.The gas proportion had obvious effects on qualities of fresh grass carp slices. 70%CO₂ and 30%N₂ package and vacuum package could control microbial growth and extend shelf life to 40 d.However the increasing of drop loss rate of fresh grass carp slices caused by vacuum package during anaphase storage had bad influence on the product value.Changes of aerobic bacterial counts of fresh grass carp slices with different gas proportion were well described by Logistic model.The gas proportion had significant effects on lag time of microorganism and shelf life of products,while no significance effects on maximum specific growth rate of microorganism.