FT-NIR for Analysis of Edible Oils

Fats and oils are recognized as essential nutrients in human diets and are presented in varying amounts in many foods. They not only provide the human body with the most concentrated source of energy, but also supply essential fatty acids that the human body needs as precursors for important hormones. The quality of edible fats and oils are assessed through parameters such as iodine value (IV), trans content, peroxide value (PV), anisidine value (AV), saponification number (SN), free fatty acids (FFA), and solid fat content (SFC). The traditional chemical and chromatographic methods used to analyze edible fats and oils are labor intensive, require the use of solvents and reagents, and are extremely time consuming.

Optical spectroscopic analysis of fats and oils is rapid, requires no sample preparation, and can analyze multiple parameters with a single measurement. An infrared spectrum of an oil contains a wealth of information that can be used to determine important parameters. For example, the OH stretching region of the infrared spectrum can indicate the presence of moisture or hydroperoxides, the latter commonly measured by the chemical PV test. The intensities of the bands in the CH region and of the ester linkage absorption are related to the average molecular weight of oil, commonly evaluated by SN determinations. The COOH absorption is indicative of lipolysis or free fatty acid (FFA) content of an oil. The presence of spectral features related to aldehydes and ketones as well as conjugated dienes is indicative of the accumulation of secondary oxidation products commonly measured by the thiobarbituric acid (TBA) test or the AV test. The isolated trans band provides a direct measure of isolated trans isomers and the combination of CH cis and CH trans absorptions provides a measure of total unsaturation or IV. The complete spectrum of a refined, melted fat characterizes its overall triglyceride composition, which in turn can be related to its SFC and also provides information about the relative amounts of saturated, monounsaturated, and polyunsaturated fatty acids in a fat or oil.

Near-infrared (NIR) spectroscopy techniques, such as FT-NIR, contains the combination bands and overtones of fundamental vibrations in the infrared region and also provides several practical advantages over infrared spectrsocopy.  For example, while infrared measurements require direct contact with the sample, NIR can measure oil samples in disposable glass vials which greatly reduces the risk of cross contamination. NIR spectra can also be measured on-line with a fiber optic probe.

NIR spectroscopy has been recognized by AOCS (American Oil Chemist Association) and AOCS method Cd1e-01 uses FT-NIR to measure Iodine Value (IV). At the same time, it has also proven to be a useful tool in the detection of oil adulteration.

Galaxy Scientific offers both off-line and on-line FT-NIR solutions for analysis of edible fats and oils. Our QuasIR™ 2000 process FT-NIR with transmission probe can be used for on-line or in-process measurements The QuasIR™ 4000 FT-NIR, equipped with a temperature controlled sample compartment, is ideal for precision off-line measurements.

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