Influence of fatty acid chain length and unsaturation on mid-infrared milk analysis

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 mu m ( 2,851 cm(-1)), and bandwidth of 0.032 mu m (26 cm(-1)); fat B reference, 3.556 mu m (2812 cm(-1)), and bandwidth of 0.030 mu m (24 cm(-1)); lactose sample, 9.542 mu m (1,048 cm(-1)), and bandwidth of 0.092 mu m (20 cm(-1)); lactose reference, 7.734 mu m (1,293 cm(-1)), and bandwidth of 0.084 mu m (14 cm(-1)); protein sample, 6.489 mu m (1,541 cm(-1)), and bandwidth of 0.085 mu m (20 cm(-1)); protein reference, 6.707 mu m (1491 cm(-1)), and bandwidth of 0.054 mu m (12 cm(-1)); fat A sample, 5.721 mu m (1,748 cm(-1)), and bandwidth of 0.052 mu m (16 cm(-1)); fat A reference, 5.583 mu m (1,791 cm(-1)), and bandwidth of 0.050 mu m (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.