Modeling Pseudomonas Spp. Growth In The Modified Atmosphere Packaged Chilled Pork And Package Optimization

The main purpose of this paper was to study the growth rule of Pseudomonas spp., oneof specific spoilage organisms of the MAP (modified atmosphere packaged) chilled pork,under different percentage of CO2and O2. Predicted microbiological theory was used toestablish the growth probability model and the time-to-detected model of Pseudomonasspp., respectively, to establish growth boundary as well. These two mathematic modelscould be applied to predict the growth of Pseudomonas spp. without traditionalmicrobiological inspection; moreover, the quality change of the MAP chilled pork wasstudied under some MAP conditions which were chosen by models in order to obtain themost optimized package for chilled pork. The conclusions of this paper were shown asfollows:Firstly, the disinfected pork was inoculated with Pseudomonas spp., and Logisticmodel was used to establish the growth probability model and the growth/no growthboundary of three initial inoculation Pseudomonas spp. in different modified atmospherepackaged at (4±1)℃. The results indicated that the Logistic model performed well, becausethe determination coefficient (r2) of the model was higher than0.85, and the determinationcoefficient (R2) of observed data and predicted data were all higher than0.95, as well as thepredicted accuracy was higher than93.3%.The result also showed that the growth probability was affected by the percentage ofCO2and O2, together with initial inoculation. Without CO2or with low percentage of CO2,the growth probability of Pseudomonas spp. increased when the percentage of O2or theinitial inoculation increased. Otherwhile, with high percentage of CO2, the probabilitydecreased even to be0, and it had no effects by the percentage of O2and initial inoculation,respectively.Furthermore, four predicted conditions of the probability model were defined as“success-safe”,“success-dangerous”,“failure-safe” and “failure-dangerous”, respectively,in this paper, resulting to evaluate the validity of the model and to ensure the safe choice ofthe atmosphere condition.Secondly, Linear regression was used to establish the TTD (time-to-detection) modelof Pseudomonas spp. in different atmosphere conditions. The results indicated that TheTTD model performed well, because the regression coefficient (r2) of the model was higher than0.959, and the determination coefficient (R2) of observed data and predicted data wereall higher than0.986, as well as Bfand Afwere1.012and1.086respectively, both near1.These results proved the TTD model to be one of valuable models to predict the shortesttime when Pseudomonas spp. could be detected in this condition.Meanwhile, the time to detection was influenced by the percentage of CO2and O2,together with initial inoculation. Without CO2, the TTD would decrease when thepercentage of O2increased. But TTD would increase when the percentage of CO2increased.TTD reduced significantly when initial inoculation increased, however, the decrease inTTD was not apparent when initial inoculation was over102CFU/mL.Thirdly, referring to the growth probability model and TTD model, respectively, sixmodified atmosphere packaged conditions were chosen, under which the growth probabilityof Pseudomonas spp. was below0.5, and the TTD was below4d. By determining the totalplate count, physicochemical parameters and sensory parameters of the chilled pork whichwere stored under these conditions, it proved to be that under40%CO2,40%O2and20%N2, the total plate count did not achieved spoilage standard, and the value of pH, TVB-Nand TBA were all within acceptable range in accordance to fresh pork standardMeanwhile, the drip loss, color and sensory quality were all superior to them stored underother conditions. So under the modified atmosphere package of40%CO2,40%O2and20%N2, the quality of chilled pork was the best in7d shelf life.In a conclusion, the condition of40%CO2,40%O2and20%N2proved to be the mostoptimized modified atmosphere package for the MAP chilled pork. Under this condition,the growth of Pseudomonas spp., the specific spoilage organisms, could not only beinhibited, but also give favorable quality for the chilled pork. This study providedtheoretical reference for the choice of atmosphere condition in the chilled pork production.