| Quick-frozen dumplings were frozen fastly, stored and transported below-18℃. Dumplings were made of fillers and wheat flour dough; the fillers generally include meat, vegetable, salt, and other auxiliary materials. Staphylococcus aureus is one of the most important security risks of frozen dumplings. In this paper, the growth kinetics model of Staphylococcus aureus in dumpling fillers were established, the bacteria changes of dumplings under different storage conditions (freeze-thaw cycle, food cold chain and frozen storage) were investigated by microbial identification of classical methods and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), the quality changes of dumplings were investigated at the same time. The specific studies and results are as follows:1. The growth kinetics model of Staphylococcus aureus in dumpling fillers were established in this study. Dumplings fillers were inoculated with Staphylococcus aureus, and then were placed at4,10,15,20and25℃for storage. The growth of Staphylococcus aureus at different temperatures was fitted by Sigmaplot11.0program. The results showed that growth of Staphylococcus aureus in dumplings fillers could be well described by Gompertz model during10to25℃. The relationship between temperature and maximum specific growth rate (μmax),lag phase (Lag) of Staphylococcus aureus expressed a good linearity by Belehradek model. The growth models of Staphylococcus aureus at13℃and18℃were built to validate the built Gompertz model, bias factors were0.991and0.988, accuracy factors were1.002and1.000. It proved the built model could describe the growth of Staphylococcus aureus during10to25℃effectively.2. Effects of temperature fluctuations caused by repeated freezing and thawing conditions on dumplings’microorganisms were investigated, as well as quality changes of dumplings. Dumplings fillers were inoculated with Staphylococcus aureus to analyse the effect of presence of Staphylococcus aureus on other bacteria. Results showed that the number and species of bacteria in dumplings increased significantly (P<0.05), Staphylococcus sp., Lactic acid bacterium, Pseudomonadales bacterium and Brochothrix thermosphacta were the main bacteria. The quality changes of dumplings were significantly (P<0.05):moisture content decreased from55.97%to35.54%; Color parameter a*-value of dumpling fillers decreased during freeze-thaw cycle, from12.23to5.98; TBARS of dumpling fillers increased from0.35mg/kg to4.18mg/kg; pH value of two treatment groups had significant differences, pH value of team that inoculated with Staphylococcus aureus was lower than normal processing group; cooking loss increased significantly (P<0.05), from19.40%to26.7%.3. The food cold chain was simulated to study the changes of dumplings’microorganisms and quality. Results showed that food cold chain could restrain effectively growth and reproduction of microbe, the number and species of bacteria were significantly lower than freeze-thaw cycle, Staphylococcus sp., Lactic acid bacterium, Pseudomonadales bacterium were the main bacteria. The quality changes of dumplings were significantly smaller than freeze-thaw cycle:moisture content decreased significantly from61.2%to50.01%; Color parameter a*-value of dumpling fillers changed little, from11.83to9.14; TBARS of dumpling fillers changed insignificantly, from0.32mg/kg to0.40mg/kg; pH value of two treatment groups had insignificant differences; cooking loss increased from20.2%to22.93%.4. Dumplings stored below-18℃could restrain effectively growth and reproduction of microbe, the number of bacteria changed little during80d. Results of PCR-DGGE showed that Staphylococcus aureus, Staphylococcus sp., Lactic acid bacterium, Pseudomonadales bacterium, Brochothrix thermosphacta and Acinetobacter sp. were the main bacteria, similar with freeze-thaw cycle. But the species of bacteria were significantly lower than freeze-thaw cycle. The quality changes of dumplings were significantly smaller than freeze-thaw cycle:moisture content decreased significantly from61.02%to48.6%; Color parameter a*-value of dumpling fillers changed significantly, from11.56to8.72; TBARS of dumpling fillers increased significantly (P<0.05), from0.32to0.92; pH value changed from6.47to5.31; cooking loss increased significantly, from19.38%to25.68%. |
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