Kaylegian K E, Lynch J M, Fleming J R, Barbano D M
Northeast Dairy Foods Research Center, Department of Food Science, Cornell University, Ithaca, NY, USA.
J Dairy Sci. 2007 Feb;90(2):602-15. doi: 10.3168/jds.S0022-0302(07)71543-6.
Our objective was to determine if lipolysis or proteolysis of calibration sets during shelf life influenced the mid-infrared (MIR) readings or calibration slopes and intercepts. The lipolytic and proteolytic deterioration was measured for 3 modified milk and 3 producer milk calibration sets during storage at 4 degrees C. Modified and producer milk sets were used separately to calibrate an optical filter and virtual filter MIR analyzer. The uncorrected readings and slopes and intercepts of the calibration linear regressions for fat B, fat A, protein, and lactose were determined over 28 d for modified milks and 15 d for producer milks. It was expected that increases in free fatty acid content and decreases in the casein as a percentage of true protein of the calibration milks would have an effect on the MIR uncorrected readings, calibration slopes and intercepts, and MIR predicted readings. However, the influence of lipolysis and proteolysis on uncorrected readings was either not significant, or significant but very small. Likewise, the amount of variation accounted for by day of storage at 4 degrees C of a calibration set on the calibration slopes and intercepts was also very small. Most of the variation in uncorrected readings and calibration slopes and intercepts were due to differences between the optical filter and virtual filter analyzers and differences between the pasteurized modified milk and raw producer milk calibration sets, not due to lipolysis or proteolysis. The combined impact of lipolysis and proteolysis on MIR predicted values was <0.01% in most cases.
我们的目标是确定校准集在保质期内的脂解或蛋白水解是否会影响中红外（MIR）读数、校准斜率和截距。在4℃储存期间，对3个改良乳校准集和3个生鲜乳校准集进行了脂解和蛋白水解变质测定。改良乳校准集和生鲜乳校准集分别用于校准光学滤光片和虚拟滤光片MIR分析仪。对于改良乳，在28天内测定了脂肪B、脂肪A、蛋白质和乳糖校准线性回归的未校正读数、斜率和截距；对于生鲜乳，则在15天内进行了测定。预计校准乳中游离脂肪酸含量的增加以及酪蛋白占真实蛋白质百分比的降低会对MIR未校正读数、校准斜率和截距以及MIR预测读数产生影响。然而，脂解和蛋白水解对未校正读数的影响要么不显著，要么显著但非常小。同样，校准集在4℃储存天数在校准斜率和截距上所造成的变化量也非常小。未校正读数以及校准斜率和截距的大部分变化是由于光学滤光片分析仪和虚拟滤光片分析仪之间的差异，以及巴氏杀菌改良乳校准集和生鲜乳校准集之间的差异，而非脂解或蛋白水解所致。在大多数情况下，脂解和蛋白水解对MIR预测值的综合影响小于0.01%。
