Our first objective was to optimize center wavelengths and bandwidths for virtual filters used in a Fourier transform mid-infrared (MIR) milk analyzer. Optimization was accomplished by adjusting center wavelengths and bandwidths to minimize the size of intercorrection factors. Once optimized, the virtual filters were defined as follows: fat B sample, 3.508 microm (2,851 cm(-1)), and bandwidth of 0.032 microm (26 cm(-1)); fat B reference, 3.556 microm (2812 cm(-1)), and bandwidth of 0.030 microm (24 cm(-1)); lactose sample, 9.542 microm (1,048 cm(-1)), and bandwidth of 0.092 microm (20 cm(-1)); lactose reference, 7.734 microm (1,293 cm(-1)), and bandwidth of 0.084 microm (14 cm(-1)); protein sample, 6.489 microm (1,541 cm(-1)), and bandwidth of 0.085 microm (20 cm(-1)); protein reference, 6.707 microm (1491 cm(-1)), and bandwidth of 0.054 microm (12 cm(-1)); fat A sample, 5.721 microm (1,748 cm(-1)), and bandwidth of 0.052 microm (16 cm(-1)); fat A reference, 5.583 microm (1,791 cm(-1)), and bandwidth of 0.050 microm (16 cm(-1)). The bandwidth and its proximity to areas of intense water absorption had the largest effect on the intercorrection factors. The second objective was to quantify the impact of fatty acid chain length and unsaturation on fat B and fat A MIR measurements. Increasing the chain length increased the difference (i.e., MIR minus reference) between MIR prediction and reference chemistry by 0.0429% and by -0.0566% fat per unit of increase in carbon number per 1% change in fat, for fat B and fat A, respectively. Increasing the unsaturation decreased the difference (i.e., MIR minus reference) between MIR prediction of fat and chemistry for fat B by -0.4021% and increased fat A by 0.0291% fat per unit of increase in double bonds per 1% change in fat concentration.
Mid-infrared (MIR) milk analyzers are traditionally calibrated using sets of preserved raw individual producer milk samples. The goal of this study was to determine if the use of sets of preserved pasteurized modified milks improved calibration performance of MIR milk analyzers compared with calibration sets of producer milks. The preserved pasteurized modified milk sets exhibited more consistent day-to-day and set-to-set calibration slope and intercept values for all components compared with the preserved raw producer milk calibration sets. Pasteurized modified milk calibration samples achieved smaller confidence interval (CI) around the regression line (i.e., calibration uncertainty). Use of modified milk calibration sets with a larger component range, more even distribution of component concentrations within the ranges, and the lower correlation of fat and protein concentrations than producer milk calibration sets produced a smaller 95% CI for the regression line due to the elimination of moderate and high leverage samples. The CI for the producer calibration sets were about 2 to 12 times greater than the CI for the modified milk calibration sets, depending on the component. Modified milk calibration samples have the potential to produce MIR milk analyzer calibrations that will perform better in validation checks than producer milk-based calibrations by reducing the mean difference and standard deviation of the difference between instrument values and reference chemistry.
Based on solid fat content profiles, milk fat fractions produced by fractional crystallization procedures employing melted milk fat and milk fat dissolved in acetone were selected for incorporation into soft butter samples. Butter samples made from low melting liquid fractions or a combination of primarily low melting liquid fractions and a small amount of high melting solid fractions exhibited good spreadability at refrigerator temperature (4 degrees C) but were almost melted at room temperature (21 degrees C). Butters made with a high proportion of low melting liquid fraction, a small proportion of high melting solid, and a small proportion of very high melting solid fractions were still spreadable at refrigerator temperature and maintained their physical form at room temperature. Very high melting fractions, which provided key structural functionality in spreadable butter, were obtained from acetone fractionation. Because the use of acetone in processing may hinder or prevent commercialization of these fractions, other means to obtain very high melting fractions from milk fat should be pursued.
Our objective was to determine the validation performance of mid-infrared (MIR) milk analyzers, using the traditional fixed-filter approach, when the instruments were calibrated with producer milk calibration samples vs. modified milk calibration samples. Ten MIR analyzers were calibrated using producer milk calibration sample sets, and 9 MIR milk analyzers were calibrated using modified milk sample sets. Three sets of 12 validation milk samples with all-laboratory mean chemistry reference values were tested during a 3-mo period. Calibration of MIR milk analyzers using modified milk increased the accuracy (i.e., better agreement with chemistry) and improved agreement between laboratories on validation milk samples compared with MIR analyzers calibrated with producer milk samples. Calibration of MIR analyzers using modified milk samples reduced overall mean Euclidian distance for all components for all 3 validation sets by at least 24% compared with MIR analyzers calibrated with producer milk sets. Calibration with modified milk sets reduced the average Euclidian distance from all-laboratory mean reference chemistry on validation samples by 40, 25, 36, and 27%, respectively for fat, anhydrous lactose, true protein, and total solids. Between-laboratory agreement was evaluated using reproducibility standard deviation (s R ). The number of single Grubbs statistical outliers in the validation data was much higher (53 vs. 7) for the instruments calibrated with producer milk than for instruments calibrated with modified milk sets. The s R for instruments calibrated with producer milks (with statistical outliers removed) was similar to data collected in recent proficiency studies, whereas the s R for instruments calibrated with modified milks was lower than those calibrated with producer 2833 milks by 46, 52, 61, and 55%, respectively for fat, anhydrous lactose, true protein, and total solids.
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