Research On Multiple Repair Technology For Sublethally Injured Pathogens Of Quick-frozen Food

In this dissertation, the main pathogens were used as the researchobject. Primarily, the sublethally injured pathogens were studied in frozen storage.Secondly, the effect of native microflora of frozen dumplings on the restore ofStaphylococcus aureus was tested. Finally, we found a enrichment medium to allowthe simultaneous resuscitate growth of sublethal Staphylococcus aureus, Salmonellaspp and Listeria monocytogenes to rapid detection level. The details of this researchwere as follows:The growth curve and the maximum resistance to salt of pathogens were studied.Afterwards, entreasured the pathogens in-18℃, which were incubated to lateexponential. The counts of pathogens were determined on tryptise soy broth agarmedium supplemented with0.6%yeast extract, containing or not containing sodiumchloride. Staphylococcus aureus, Salmonella spp and Listeria monocytogenes need5,5and8hours to late exponential, and the maximum resistance to sodium chloride is10%,6%and7%, respectively.The growth of frozen-sublethal Staphylococcus aureus in tryptise soy brothcontaining0.6%yrast extract powder and10%sodium chloride trypticase soy brothwere compared. Moreover, different concentrations native microflora of frozendumplings were added in tryptise soy broth containing0.6%yrast extract powder.Both of the numbers of total microflora and Staphylococcus aureus were measuredevery towhours within24hours. Finally, Gompertz model was used to calculate thegrowth characteristics of bacteria. The results showed that:10%sodium chloridetrypticase soy broth suppressed the recovery of frozen-sublethal Staphylococcusaureus. The presence of native microflorhad inflence on the growth rate and lagperiod of frozen-sublethal Staphylococcus aureus. In addition, thehigher theconcentration of background bacteria was, the fewer Staphylococcus aureus was. To evaluate the enrichment medium for simultaneous of Staphylococcus aureus,Salmonella spp and Listeria monocytogenes, commercially available enrichmentmedium were used (buffered peptone water, nutrient broth, et al). Then, tryptise soybroth containing0.6%yrast extract powder was selected as base medium. Potassiumtellurite, lithium chloride and sodium chloride were used to inhibit the growth ofsalmonella. Through the response surface analysis, Design-Expert software wasfurther used for regression analysis of the data from experiments to build and assessmodels. The best add parameters were verified of K2TeO3, LiCl and NaCl as0.6mg/L,2.49g/L and0.6%, respectively. Under this condition, the concentration ofStaphylococcus aureus, Salmonella spp and Listeria monocytogenes reached108,107and106colony forming units per millimeter.The late exponential Staphylococcus aureus, Salmonella spp and Listeriamonocytogenes were sustained frozen stress in-40℃refrigerator for30min andheatstress at60℃for5min. To detect the simultaneous resuscitate growth of sublethalStaphylococcus aureus, Salmonella spp and Listeria monocytogenes, the cellsacquired were inoculated in optimal tryptise soy broth and the results indicated thatthe ultima bacteria satisfied rapid detection levels.