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Near-IR Improves Measurement of Fat Content

Photonics Spectra
Apr 2005
Hank Hogan

Sandra E. Kays, a research chemist at the US Department of Agriculture's Agricultural Research Service in Athens, Ga., would like to make producing the nutrition label on a cereal box as easy as reading it. Today, making the measurements for nutritional information such as overall fat can require considerable effort and expense.

Kays, graduate student Laura L. Vines and their colleagues have developed a way to relate near-infrared reflectance readings to the fat content in cereal products. Their results so far are promising with regard to the requirements of the US Nutrition Labeling and Education Act, yielding a model that is accurate enough to meet the regulations for reporting total fat, Kays said.

Near-IR Improves Measurement of Fat Content
The current method used to assess the total fat in cereal products is time-consuming and involves chemicals that require special handling and disposal.

Currently, assessing the total fat, or lipid content, in cereal and similar foods is performed with AOAC Method 996.01. This procedure takes 10 hours or more and involves the use of organic solvents and acids that require special handling and disposal. Despite these drawbacks, the method is employed by the food industry, nutrition analysis laboratories and monitoring agencies such as the Food and Drug Administration (FDA) and the Agriculture Department's Food Safety and Inspection Service.

Near-IR Improves Measurement of Fat Content
Near-IR reflectance spectroscopy displays promise as a means of assessing the total fat of cereal products in a matter of minutes and without the use of hazardous chemicals.

As an alternative, Kays' group turned to near-IR reflectance spectroscopy for a way to measure fat content quickly and with minimal processing. It worked with the NIRSystems 6500 spectrometer from Foss North America of Eden Prairie, Minn. The instrument has a spectral resolution of 10 nm and collects data every 2 nm so that there is a fivefold oversampling, which improves the signal-to-noise ratio and helps to maintain stable calibration, Kays said.

For their work, the investigators used the AOAC method to determine the total lipid content for 72 products. They milled and ground samples from the same products into pieces smaller than 500 µm in diameter, from which they collected reflectance spectra from 1104 to 2494 nm. After processing the data, they found peaks at 1162, 1212, 1728, 1760, 2308 and 2346 nm. The peaks, Kays noted, are associated with the stretching of the carbon-hydrogen bond in fats.

Near-IR Improves Measurement of Fat Content
The height of peaks associated with the stretching of the carbon-hydrogen bond in fats correlates to increasing total fat content. The near-IR technique is most accurate with samples containing more than 6 percent total fat.

The height of the peaks, the scientists report in the March 9 issue of Journal of Agricultural and Food Chemistry, correlates to increasing fat content in the food samples. From this, they developed a model and predicted AOAC readings for a validation group of 36 other products.

The near-IR reflectance method worked best when there was a strong signal from the component, which in this case meant more fat -- above 6 percent total fat, Kays said. Below that, the error ran as high as 20 percent. However, those low-fat samples had less than a gram of fat per serving. According to the Nutrition Labeling and Education Act, a reading of less than 0.5 g can be reported as zero, so errors in this range may not matter.

Work is under way to improve the infrared method and to extend it to include not only total fat, but also saturated fat. Before it can be used, the technique will have to be certified by the FDA and the Food Safety and Inspection Service. What's more, a near-IR reflectance model will have to be developed for each application.

The measurement time for the technique would be 10 minutes, according to Kays, much faster than the AOAC method. In addition, it would improve safety and eliminate solvents. There might be a high initial expense for the instrumentation, but Kays predicts substantial savings in overall costs.


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