UHT乳货架期预测模型的建立及检验

【目的】建立以原料奶体细胞数、嗜冷菌数、耐热蛋白酶活性、贮藏温度等指标来预测UHT奶货架期的预测模型，预测不同原料奶加工UHT产品的货架期。【方法】通过三因素二次正交旋转组合试验及多元线性逐步回归的方法，以煮沸试验、酒精试验结果作为UHT乳货架期的判定指标，以感官评分分数和蛋白水解度值作为辅助，监测不同品质原料奶经UHT加工后产品在不同贮藏温度下产品的主要品质指标的变化规律。【结果】通过试验得到UHT乳货架期（Y）与体细胞数SCC（X1）、蛋白酶活性（X2）以及温度(X3)三因素在编码空间的回归方程为：Y=53.94-3.46X1-6.56X2-3.52X3+0.89 X12+2.67X22+0.19X32-2.75X1X2+1.50X1X3+2.0X2X3。三因子对货架期影响显著，其中X2对货架期的影响最大（P =0.0002），其次是X3（P =0.0160），最后是X1（P =0.0173）。在三因素二次正交旋转组合试验结果基础上，采用多元线性逐步回归，得到优化的UHT乳货架期（Y）与SCC(X1)、嗜冷菌数(X2)、PL活性(X3)、总菌数(X5)、贮藏温度（X6）的模型方程Y=103.752+0.0297X1-0.0000597X2- 3.661X3-0.000316X5-0.469X6（R=0.8870，R2=0.7867）。【结论】模型通过回归系数t检验、回归方程F检验、回归标准差检验、拟合优度检验、D.W检验，平均绝对百分误差MAPE＜10，模型2预测精度较高，可用于预测。

Establishment and Test of Prediction Model for UHT Milk Shelf Life

【Objective】The objective of this study is to establish a forecasting model for predicting the shelf life of UHT milk. The model is based on somatic cell count, the number of psychrophilic bacteria, heat-stable protease activity of raw milk, preservation temperature of UHT milk and other indicators. 【Method】The quadratic orthogonal three-factor test and multiple linear stepwise regression method were used to design the experiment and to analyze the data. Boiling test and alcohol test are regarded as standard of shelf-life of UHT milk, and sensory score and determination of the degree of protein hydrolysis are regarded as a supplementary criterion. These methods were used to monitor variation of main quality of product, which were made of different qualities of raw milk by the UHT and deposited at different temperatures. 【Result】 Through the quadratic orthogonal rotatable design and analysis, SCC (X1), proteinase activity (X2) and temperature (X3) were used as independent variables, and the obtained equation is Y=53.94-3.46X1-6.56X2-3.52X3+0.89X12+2.67X22+0.19X32-2.75X1X2+1.50X1X3+2.0X2X3. The effect of three factors on shelf life was significant. Analysis of variance showed that the impact factors followed the order: X2(P=0.0002), X3(P=0.0160), X1(P=0.0173). Through multiple linear regression design, the obtained optimized model equation is Y=103.752+0.0297X1-0.0000597X2- 3.661X3-0.000316X5-0.469X6 (R=0.8870, R2=0.7867). 【Conclusion】 Equation can be used to forecast shelf life as the results of model tested and estimated successfully by t-test, F-test, D.W and MAPE, etc. The assessment standards of applicability of raw milk for UHT process was constructed.