Effects Of Controlled Freezing-Point Storage And Modified Atmosphere Packaging On Qualities And Microfloras Of Monopterus Albus Slices

Monopterus albus with rich nutrition and delicious taste is one of precious and high quality aquatic products, and far popular in China. But the market's needs can not be meet because of unsuitable transportation and lacking further processing products. Based on studies of the essential composition and effects of seasonings on the thermal properties of fresh Monopterus albus slices (mud slices) , changes of qualities and microflora of different storage temperatures, seasoning methods and package methods were researched to establish quality change and bacteria growth kinetics models of mud 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, protein, fat and ash in fresh mud fish was 81.33%, 17.88%, 0.95% and 0.97%, respectively. The freezing temperature, the freezing point and the latent heat were -10.73℃, -0.85℃C and 233.70 J/g, respectively. With adding amount of salt, sucrose and the mixture of salt and sucrose increased, content of the soluble solids would be shifted, and freezing temperature, freezing point and latent heat would be decreased. The freezing point of seasoning mud slices was negatively correlated to adding amount of salt, sucrose and the mixture of salt and sucrose obviously. The regression equations of freezing point predicted were F=-0.9754S-0.6238, F=-0.1287T-0.6634, F=-0.8166-0.7609S-0.0398T-0.0340S²-0.0042ST-0.0124T², respectively.2. The storage temperatures had significant effects on qualities and shelf life of mud slices. Changes of aerobic bacterial counts, total volatile basic nitrogen (TVB-N) value and histamine with storage time increased was fixed the first order kinetics model. Under non-frozen state, the growth rate constant of aerobic bacterial counts, TVB-N and histamine increased with storage temperature added. The growth rate constant of those indicators was fixed Arrhenious equation significantly. The time of histamine overruning the limite of national regulate was far behind that of aerobic bacterial counts exceeding. According to aerobic bacterial counts, the predictive shelf life at 25.0℃, 5.0℃, -0.5℃was 0.14d, 5.12d, 17.01d, respectively.3. The microfloras of mud slices was influenced significantly by the storage temperatures. Pseudomonae was the most popular bacteria in fresh mud slices, Lactococcus secondly and Micrococcus, Enterbacteriaceae, Enterococcus were the least. The growth rate of Pseudomonae, Lactococcus, Micrococcus, Enterbacteriaceae, Enterococcus increased with storage temperatures increased. The activation energy of Enterococcus, Micrococcus and Pseudomonae were 41.37J/mol, 29.74 J/tool and 29.81 J/mol, respectively.4. The salt and sucrose seasonings had some effects on preservation quality of mud slices. The mud slices with 2.5% salt seasoning could inhibit microbial and TVB-N growth rate significantly, remaining high water-holding capacity. However, 2.0% sucrose seasoning could promote microbial growth and decrease water-holding capacity. The shelf life of mud slices with 2.5% salt seasoning was prolonged to 9d at 5.0℃and 20d at -0.5℃, which was two or three days longer than that of fresh mud slices.5. The package methods had obvious effects on qualities and microfloras of mud slices. Vacuum package and 100% CO₂ package could control microbial growth and extended shelf life to 23d, however vacuum package would increased the drop loss rate of the mud slices. With storage time increased, the proportion of Pseudomonae was declined, while the proportion of Lactococcus rised sharply and became the predominant spoilage organism gradually in oxygen-excluded package. And Enterococcus was the main spoilage organism in 100% CO₂ package.