Upreti P, Metzger L E
MN-SD Dairy Foods Research Center, Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108, USA.
J Dairy Sci. 2006 Jun;89(6):1926-37. doi: 10.3168/jds.S0022-0302(06)72260-3.
The methods available for measuring organic P and bound Ca in cheese are either cumbersome or involve dilution of the cheese. Dilution of the cheese can lead to erroneous results, particularly in the case of bound Ca. Hence, the objective of this study was to evaluate the feasibility of Fourier transform infrared (FTIR) spectroscopy for direct measurement of organic P and bound Ca in Cheddar cheese. Two hundred sixteen samples of cheese were analyzed for protein-bound organic P, bound Ca using a water-extraction based method, and buffering curves. Additionally, the infrared spectra of the cheeses were collected between 4,000 and 650 cm(-1), at a resolution of 4 cm(-1), and 256 scans per sample. The spectral shifts in the infrared region from 1,050 to 900 cm(-1), in addition to the measured concentrations of organic P, bound Ca, and buffering peak area at pH 5.1, were used to develop calibration models using partial least squares (PLS) regression analysis. The spectral region of 956 to 946 cm(-1) correlated with the measured concentrations of organic P and the overall PLS model had a correlation (R2) of 0.76 between the predicted and measured concentrations. The spectral region at approximately 980 cm(-1) was correlated with the measured concentrations of bound Ca, and the overall PLS model had a correlation (R2) of 0.70 between the predicted and measured concentrations. A similar spectral region at approximately 980 cm(-1) was also correlated with the measured buffering peak areas and the overall PLS model had a correlation (R2) of 0.64 between the predicted and measured peak areas. A linear regression analysis between the bound Ca and buffering peak area demonstrated that bound Ca was correlated (R2 = 0.73) with buffering peak area. This study demonstrates that FTIR can be used to measure organic P in cheeses. It also has the potential to be used for measuring bound Ca in undiluted cheeses, and for prediction of the buffering capacity of cheese.
用于测量奶酪中有机磷和结合钙的现有方法要么繁琐，要么需要对奶酪进行稀释。奶酪稀释可能会导致结果错误，尤其是在结合钙的情况下。因此，本研究的目的是评估傅里叶变换红外（FTIR）光谱法直接测量切达干酪中有机磷和结合钙的可行性。使用基于水提取的方法分析了216个奶酪样品中的蛋白质结合有机磷、结合钙，并绘制了缓冲曲线。此外，在4000至650 cm(-1)范围内收集奶酪的红外光谱，分辨率为4 cm(-1)，每个样品扫描256次。除了测量的有机磷、结合钙浓度和pH 5.1时的缓冲峰面积外，还利用1050至900 cm(-1)红外区域的光谱位移，通过偏最小二乘法（PLS）回归分析建立校准模型。956至946 cm(-1)的光谱区域与测量的有机磷浓度相关，整个PLS模型预测浓度与测量浓度之间的相关性（R2）为0.76。约980 cm(-1)的光谱区域与测量的结合钙浓度相关，整个PLS模型预测浓度与测量浓度之间的相关性（R2）为0.70。约980 cm(-1)的类似光谱区域也与测量的缓冲峰面积相关，整个PLS模型预测峰面积与测量峰面积之间的相关性（R2）为0.64。结合钙与缓冲峰面积之间的线性回归分析表明，结合钙与缓冲峰面积相关（R2 = 0.73）。本研究表明，FTIR可用于测量奶酪中的有机磷。它还具有用于测量未稀释奶酪中结合钙以及预测奶酪缓冲能力的潜力。
