Effect of Multiple Freeze-thaw Cycles on the Microflora of Quick-frozen Dumplings
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Abstract:
The effect of temperature fluctuations caused by repeated freeze-thaw cycles on the number and diversity of microorganisms in quick-frozen dumplings was investigated using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and traditional plate culture methods. The dumpling fillers were inoculated with Staphylococcus aureus to analyze the dynamic changes in S. aureus itself and its influence on the dumpling microflora. The results showed that the quantity and diversity of microorganisms in the dumplings increased significantly (p < 0.05) with increasing freeze-thaw cycles. At the last cycle, S. aureus count in the inoculated dumplings increased from 3.49 to 5.07 log10 CFU/g, which reached the minimum count for Staphylococcal toxicity, of 105 CFU/g. PCR-DGGE showed that lactic acid bacteria, Pseudomonadales bacterium and Brochothrix thermosphacta were the dominant strains in the dumplings during the freeze-thaw cycles, while the counts of S. aureus increased and finally became the dominant strain. The results of PCR-DGGE and the traditional culture method were generally consistent.
