液态乳中荧光假单胞菌生长及产酶情况分析

Analysis of Growth and Protease Production of Pseudomonas Fluorescens in Liquid Milk

为研究液态乳中荧光假单胞菌的生长和产酶情况,选用UHT乳为研究对象,接种高、中、低浓度的荧光假单胞菌(CICC23251)置于4℃和28℃培养。选用Baranyi&Roberts、修正Gompertz和修正Logistic模型为一级模型,运用DMFit和Origin 9.0软件对荧光假单胞菌生长数据进行拟合,利用决定系数和均方误差判断拟合优度。应用偶氮酪蛋白法测定荧光假单胞菌的产蛋白酶情况。结果表明,修正Gompertz模型可得到较高的决定系数(>0.999)和较低的均方误差(<0.069),通过预测模型拟合发现在28℃时,高浓度荧光假单胞菌最大生长速率较低,而在4℃时,高浓度荧光假单胞菌高于其他浓度细菌的生长速率。应用Logistic模型研究荧光假单胞菌菌落数与产蛋白酶的关系,4℃时,决定系数在0.95~0.99之间,28℃时,决定系数均大于0.80。蛋白酶经75℃和85℃加热180 min后,仍分别有16.05%+2.09%和9.30%+0.75%的残余。该研究可为液态乳中荧光假单胞菌的生长、产酶情况,以及货架期预测提供理论支持。

In order to study the growth behaviors and protease production of Pseudomonas fluorescens in liquid milk,high,medium,and low inoculum of Pseudomonas fluorescens were inoculated into the UHT milk.The samples were incubated at 4℃ and 28℃.Growth curves were fitted by using the Baranyi&Roberts model,modified Gompertz model and modified Logistic model.DMFit and Origin 9.0 software were used to fit the data and the goodness of mode was determined by the coefficient of determination and mean square error.The azocasein method was applied to determine the protease production of Pseudomonas fluorescens.The results showed that the modified Gompertz model fitted well with the high coefficients of determination(R^(2)>0.999)and the low mean square error(MSE<0.069).By fitting the predictive model,it was found that the maximum growth rate of high inoculum of Pseudomonas fluorescens was lower than the other two inoculum at 28℃,however,at 4℃,the maximum growth rate of high inoculum was higher than the others.The Logistic model was applied to illustrate the relation between the numbers of Pseudomonas fluorescens and protease amount,the coefficient of determination ranged from 0.95 to 0.99 when the strains were incubated at 4℃,and the coefficient of determination was more than 0.80 when incubated at 28℃.After heating at 75℃ and 85℃ for 180 min,(16.05±2.09)% and(9.30±0.75)% of protease was remained.This study can provide theoretical support for understanding the growth and protease production of Pseudomonas fluorescens,which can contribute to predicting the shelf life of liquid milk in the future.