真空预冷处理对大肠杆菌O157:H7在卷心菜中渗透的影响

Effect of Vacuum Cooling Treatments on the Filtration of E. coli O157:H7 into Fresh Lettuce

摘要:

利用风冷、真空预冷等技术对接种大肠杆菌O157:H7的卷心菜进行预冷，预冷后无菌包装并放置于5±2℃冷库贮藏。通过测定卷心菜预冷以及贮藏过程中的总的及内部的大肠杆菌数量来评价其对卷心菜的影响。结果表明，较风冷后卷心菜内部和总的大肠杆菌数量1.9×103和2.3×106 cfu/g而言，真空预冷操作方式后内部的数量均高于4.5×103 cfu/g，而总的数量均低于1×106 cfu/g。同时，真空预冷抽气速率越快、终压值越低及复压操作时间越短均会导致渗透至组织内部的大肠杆菌数量越多，同样导致总的大肠杆菌下降的数量也越多。风冷后的卷心菜在贮藏3 d后其总的大肠杆菌数量下降率为69.57%，而真空预冷的下降率则均高于90.00%。同理，较贮藏3 d后的风冷的卷心菜内部的大肠杆菌数量1.1×102 cfu/g而言，真空预冷则均高于1.5×102 cfu/g。所以，真空预冷之前控制总的大肠杆菌的数量以及合理的抽气速率0.229 min-1、操作终压值1500 Pa和复压操作时间9 min更有利于控制卷心菜的质量安全。该研究结果为真空预冷过程中大肠杆菌渗透至卷心菜中的内部的机理提供了参考依据。

Abstract:

The technology of air cooling, vacuum cooling with different evacuation rate, final pressure value and repressuring time utilized to lower the temperature of iceberg lettuce were investigated in this work. All of samples were stored at the temperature of 5±2 ℃ after cooling. the indice including the total and internal Escherichia coli O157:H7 cell counts were detected to evaluate the effects of different evacuation rates, final pressure values and repressuring times on the iceberg lettuce. Effects of different evacuation rates, final pressure values and repressuring times on the variation of the total and internal Escherichia coli cell counts during cold storage were also evacuated. The results showed that all vacuum cooling methods had a more internal cell conts of Escherichia coli of 4.5×103 cfu/g and less total cell counts of Escherichia coli of 1×106 cfu/g compared to the internal and total cell conts of Escherichia coli of 1.9×103 cfu/g and 2.3×106 cfu/g subjected to air cooling. It was found that higher evacuation rates, lower final pressure value and quicker repressuring time led to a more infiltration of Escherichia coli into the inner of iceberg lettuce. Compared to air cooling, vacuum cooling was more effective to decrease the cell counts of total Escherichia coli. Compared to the reduction rate of 69.57% of the total cell conts of Escherichia coli after 3 d cold storage, all vacuum cooling methods had a more reduction rate of 90%. All vacuum cooling methods had a higher internal Escherichia coli cell counts of 1.5×102 cfu/g after 3 d cold storage than 1.1×102 cfu/g subjected to air cooling. It was reasonable to assumed that controlling the cell counts of Escherichia coli before vacuum cooling and adjusting properly the evacuation rate of 0.229 min-1, final pressure value of 1500 Pa and repressuring time of 9min might be a effective method to assure the quality and safety of leaf vegetable. These above-mentioned conclusions could provide a reference for the mechanism of filtration of Escherichia coli into the inner of iceberg lettuce.