Pseudomonas Aeruginosa Inhibiting Optimization, Models Establishment, Water Holding Capacity And Protein Of Pork Affected By Sodium Lactate

The coordinated inhibition effect of sodium lactate(Na L), tea polyphenol(TP) and chitosan on the growth of Pseudomonas aeruginosa(separated from spoilage pork) in chilled pork was studied in this thesis by using constant broth dilution method and an agar disc diffusion assay. The optimal proportion of concentration of three preservatives was determined by response surface methodology, meanwhile, the results showed that Na L played a dominant effect among three preservatives in our study. Then, the cardinal parameters model(CPM) as a function of temperature, pH and sodium lactate was developed to obtain the cardinal parameters of P. aeruginosa, namely lagopt, Tmin, Topt, Tmax, pHmin, pHopt, pHmax and the minimum inhibitory concentrations of sodium lactate. In addition, the effects of different concentrations of sodium lactate on the water holding capacity, expression of protein and change of heat flow of longissimus dorsi of pork were studied in this study. The contents and conclusions conclusions of this dissertation were as follows:Firstly, the coordinated inhibition effect of NaL, TP and chitosan on the growth of P. aeruginosa was studied by using constant broth dilution method and an agar disc diffusion assay. Using constant broth dilution method, the minimum inhibitory concentrations(MICs) of sodium lactate, tea polyphenol and chitosan were obtained, and subsequently the corresponding MICs were utilized for the determination of the inhibition effect of single preservative. Besides, the quadratic polynomial regression equations of three preservatives were established by the Box-Behnken design for the further analysis. Results showed that the descending order of three preservatives antimicrobial effectiveness was as follows: NaL, chitosan and TP. Moreover, the interactive effect of NaL and TP was very significant different(p < 0.01), and interactive effect of Na L and chitosan was significant different(p<0.05). However, There was no significant interactive effect of TP and chitosan(p>0.05). The best inhibitory effect for P. aeruginosa occurred with the combination of 62.5 mg/m L sodium lactate and 3.17 mg/mL chitosan.Secondly, a CPM, representing the lag time of P. aeruginosa as a function of temperature, pH and sodium lactate mass concentration, was established. An automated turbidimetric system, Bioscreen C, was used to acquire the growth curves of P. aeruginosa at a range of temperature(25~40 ℃), pH(5.0~7.5) and mass concentration of sodium lactate(0~0.035 g/m L). This CPM was established by the fminsearch function in Matlab software on the basis of nonlinear least squares method, and subsequently, the MIC of NaL and the cardinal parameters such as lagopt, Tmin, Topt, Tmax, pHmin, pHopt and pHmax could be obtained. Ten random data within above ranges were applied for the validation of the established CPM. The performance of CPM for predicting the growth parameters of P. aeruginosa was satisfying with R2= 0.9291, Bf= 1.0975, Af= 1.3936 for the calibration set and R2=0.8546, Bf =1.1225, Af=1.2117 for the validation set, respectively.Thirdly, the effects of different concentrations of sodium lactate on the water holding capacity, expression of protein and change of heat flow of longissimus dorsi of pork were studied. The longissimus dorsi samples cut into 1 cubic centimeters were immersed in different concentrations of Na L solution and prepared for further experiments. The results showed that the low concentration(1%, 2%, 3%, 4% and 5%, respectively) had water holding capacity to pork, meanwhile, the higher concentration of sodium lactate, the better the water holding capacity, however, high concentration of sodium lactate solutions(10%, 20% and 30%, respectively) would lead to water loss of the pork. The results of SDS-PAGE electrophphoretogram and DSC thermograms showed that the protein of pork immersed in high concentration of sodium lactate solutions was changed significantly. In a conclusion, the high concentration of sodium lactate solutions would cause the water loss and protein denaturation of pork.In summary, the coordinated inhibition effect of Na L, TP and chitosan on the growth of P. aeruginosa was verified, and the CPM as a function of temperature, p H and sodium lactate mass concentration were established, and the influences of different concentrations of sodium lactate on water holding capacity, protein on longissimus dorsi of pork were discussed. This study could provide a theoretical reference for predicting the growth of P. aeruginosa under different environment and prolonging shelf life of chilled pork.