Study On Controlled Freezing-point Storage And Modified Atmosphere Packaging Technology For The Preservation Of Oysters

The changes of quality and microflora of Pacific oysters stored under freezing-point and modified atmosphere package were studied in this paper.Based on the results of study on changes of qulities and microflora, the qulity change and shelf life prediction kinetics models of oysters under controlled freezing-point storage and modified atmosphere packaging were established, and the HACCP system was also established. The main results summarized as following:1.Aerobic bacterial counts and total volatile basic nitrogen(TVB-N) value of oysters increased with storage time. Free amino acid nitrogen(FAAN) value decreased at initial period of storage, then increased. The storage temperatures had significant effects on qualities and shelf life of oysters. Changes of aerobic baeterial counts, total volatile basic nitrogen(TVB-N) value with storage time were fit for the first order kinetics model. Under non-frozen state, the growth rate constant of aerobic baeterial counts, TVB-N increased with storage temperature. The growth rate constant of those indicators was fixed Arrhenious equation significantly. According to aerobic baeterial counts, TVB-N value and sensory evaluation, the predictive shelf life of oyster under 4℃, controlled freezing-point was 6.2d,11.3d, respectively. The dominant ogranisms were found to be Pseudomonas regardless of the storage temperatures2. Two factors quadratic general design is applied by the properties of the main bacteria causing the spoilage of oysters in the experiment. Regress equation (y=0.0389+0.0053x1+0.0119x2+0.0008x1x2-0.0013 x12-0.0018 x22)was obtained. The optimized composition of a sort of combined preservative was lysozyme 0.025% +tea polyphenols 1.0%. The preservatives extended the shelf life of oysters by 5-6 days at the same temperature. At the end of shelf life, the dominant organism was Psuedomonas(proportion of 38.1%), the preservatives did not alter the dominant organisms in the process of spoilage, but the proportion of Psuedomonas was declined.3.The different package methods had obvious effects on qualities and microflora of oysters. Among the three different package methods(Atmosphere package,Vacuum package and 40% CO2:40% O2:20% N2 package),Vacuum package and 40% CO2:40% O2:20% N2 package controlled microbial growth and extended shelf life of oyster to 20d, however vacuum package increased the drop loss rate of oysters.With storage time increased, the proportion of Psuedomonas was declined, while the proportion of Lactococcus rised sharply and became the predominant spoilage organism gradually in 40% CO2:40%O2:20% N2 package.4.Of all the processing of postharvest storage, scrubbing and storage were found to be the critical control points, and thereby the HACCP system was established.5. The keeping alive technology in ecological freezing temperature of oysters was investigated preliminary, the result showed that the survival rate of oyster was 92% after holding 4 days at ecological freezing temperature.