| Staphylococcus aureus is one of the most important foodbornepathogens in quick-frozen food, and raw meat is an important source of S. aureus infrozen food. How to remove effectively the bacteria in raw meat is of greatsignificance for frozen food security control. The research object of this experimentwas a strains of Staphylococcus aureus ATCC8095, which is the common pathogenicbacteria in frozen food. The research would get optimization result of the compositenatural bacteriostatic agent of Staphylococcus aureus in raw meat of quick-frozenfood based on the research of the natural antibacterial effects on Staphylococcusaureus. The details of this research were as follows:The research selected the four kinds of common natural bacteriostatic agent:Betaine(Bet), Lactic acid, Glycerol monolaurate(GML), Chitin, using the K-B papermethod to compare analyze their antibacterial activity against Staphylococcus aureusand determine their inhibition zone diameters with filter paper. While, using thedouble dilution method determines the minimum inhibitory concentration(MIC). Theminimum inhibitory concentration of the four natural bacteriostatic agents were asfollows: betaine6.25mg/ml, lactic acid18mg/ml, glycerol monolaurate17μg/ml,chitin50mg/ml. This research is intended to provide theoretic support to the activityof natural bacteriostatic agent effcts on food pathogenic microbe.Firstly, according to the above research results determine the suitableconcentration of betaine, Secondly, to analysis betaine effect on growth curve ofStaphylococcus aureus under different environmental conditions, with measured thenumber of Staphylococcus aureus every hour within eight hours and to simulation ofthe growth parameters by the application of Gompertz model. The results showed thatbetaine has inhibitory effect on Staphylococcus aureus (the optimum growth is37℃)when grows with adverse environmental conditions (10or45℃). The application ofGompertz model to simulation of the growth parameters of Staphylococcus aureus under the betina concentrations of10mg/ml,25mg/ml,50mg/ml get the result of thepseudo-R2which was above0.90. This is showed that the equation can be a very gooddescription of the growth dynamic rules of Staphylococcus aureus. The number of S.aureus was reduced with the addition of the concentration of betaine (25mg/ml and50mg/ml), especially when the concentration of betaine is50mg/ml, it can be inhibiteffectively the maximum specific growth rate of S. aureus, with strong antibacterialability. When the concentration of betaine is25mg/ml, there would be a longer lagtime, which can effectively prolong the growth of S. aureus. The lag time would beshorten when added the high concentration of betaine.By addition of S. aureus which is growth at late exponential stage into the rawpork of quick-frozen food, then put them in enrich culture. We optimized optimumbacteriostatic formula S. aureus in the raw pork by choosing Lactic acid, Glycerolmonolaurate(GML) and Soak time as response surface, using the growth logarithmvalues of S. aureus in the raw pork as the response value. The experiment used theresponse surface method (RSM) and constructed the response surface model. Theexperiment showed that lactic acid, glycerol monolaurate and soak time inhibited thegrowth of S. aureus in the raw pork and the addition of bacterial colony number, andthen finally decreased the number of S. aureus and colony number. This is concernedwith inhibiting effect of added material and the characteristics of S. aureus. Throughthe RSM experiments, we get the optimum formula of composite bacteriostatic agent:lactic acid0.49%, glycerol monolaurate0.54%, and soak time5.51min, with thenumber of S. aureus and colony number were4.20log (CFU/ml) and4.31log(CFU/ml). The number of S. aureus and colony number were8.06log (CFU/ml) and8.11log (CFU/ml). Through the optimum formula which couled reduce effectivelythe number of S. aureus and colony number in the raw pork, and basically had noeffect on the quality of the raw pork. |
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