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Influence of fatty acid chain length and unsaturation on mid-infrared milk analysis¹

K. E. Kaylegian^*, J. M. Lynch^*, J. R. Fleming and D. M. Barbano^*,2

^* Northeast Dairy Foods Research Center, Department of Food Science, Cornell University, Ithaca, NY 14853
USDA, Agricultural Marketing Service, Southwest Milk Marketing Area, PO Box 110939, Carrollton, TX 75011

² Corresponding author: dmb37{at}cornell.edu

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

Key Words: infrared • fatty acid composition • interference filter

This article has been cited by other articles:

				K. E. Kaylegian, D. A. Dwyer, J. M. Lynch, D. E. Bauman, J. R. Fleming, and D. M. Barbano Impact of fatty acid composition on the accuracy of mid-infrared fat analysis of farm milks J Dairy Sci, June 1, 2009; 92(6): 2502 - 2513. [Abstract] [Full Text] [PDF]