Edible oil analysis by FTIR spectroscopy

Laboratory Robotics and Automation 12/1998; 8(4):205 - 212. DOI: 10.1002/(SICI)1098-2728(1996)8:4<205::AID-LRA2>3.0.CO;2-4

ABSTRACT Fourier-transform infrared (FTIR) spectroscopy offers a new way of approaching edible oil analysis and is well on its way to being developed into a utilitarian quality control tool. This paper provides a brief overview of FTIR spectroscopy, the key elements associated with developing a suitable fats and oils analytical system (sample handling, calibration development, validation, calibration stability and transfer, programming and automation), some methods that have been implemented, and the basic elements of a typical fats and oils FTIR analytical package. It is foreseen that a number of standard AOCS methods will be replaced by this technology, allowing a variety of chemical and physical analyses to be carried out on neat fats and oils in under 2 minutes per sample. © 1996 John Wiley & Sons, Inc.

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    ABSTRACT: A method for the simultaneous determination of iodine value (IV) and trans content from the Fourier transform infrared (FTIR) spectra of neat fats and oils recorded with the use of a heated single-bounce horizontal attenuated total reflectance (SB-HATR) sampling accessory was developed. Partial least squares (PLS) regression was employed for the development of the calibration models, and a set of nine pure triacylglycerols served as the calibration standards. Regression of the FTIR/PLS-predicted IV and trans contents for ten partially hydrogenated oil samples against reference values obtained by gas chromatography yielded slopes close to unity and SD of <1. Good agreement (SD<0.35) also was obtained between the trans predictions from the PLS calibration model and trans determinations performed by the recently adopted AOCS FTIR/SBHART method for the determination of isolated trans isomers in fats and oils.
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    ABSTRACT: Over the past 20years, Fourier transform infrared (FTIR) spectroscopy has evolved to become an important tool for quantitative analysis, and its application to edible oil analysis has been an active area of research. This paper reviews the evolutionary development of methodology for FTIR analysis of edible oils in our laboratory, focusing on strategies and techniques used to quantitate a variety of common edible oil quality control parameters, such as free fatty acid content, iodine value, saponification number, peroxide value, solid fat index, trans content, moisture content, anisidine value, etc., as well as conceptual, instrumental, and software/automation innovations originating in related work on lubricant analysis. In our initial development of FTIR methods for edible oil analysis, the calibration approaches employed were mainly based on partial-least-squares regression using either molecular model systems or process samples. Subsequently, the concept of signal transduction was developed as a means of facilitating the routine implementation of some of these FTIR methods and was also considered for the analytically related lubricant sector. However, the viscosity, complexity, and matrix variability of in-service lubricants required new approaches, while the high sample volumes common to the field made automation a prerequisite. These issues were addressed through the use of signal transduction in combination with dilution as well as extraction techniques to facilitate automation while maintaining quantitation. A related concept, termed spectral reconstitution, was initially developed to speed up the qualitative condition monitoring of in-service lubricants. Spectral reconstitution was subsequently successfully applied to trans analysis in edible oils and was shown to provide a generalized means for high-volume FTIR transmission analysis of viscous oils. This technique has since been adapted to quantitative peroxide value and free fatty acid analysis, allowing for throughputs of up to 120 samples per hour. These developments represent the integration of analytical methodologies for the edible oil and lubricant sectors, with potential for extension to the fuel sector as triacylglycerols become a feedstock for biodiesel.
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    ABSTRACT: A Fourier transform-near infrared (FT-NIR) method originally designed to determine the peroxide value (PV) of triacylglycerols at levels of 10–100 PV was improved upon to allow for the analysis of PV between 0 and 10 PV, a range of interest to the edible oil industry. The FT-NIR method uses convenient disposable glass vials for sample handling, and PV is determined by spectroscopically measuring the conversion of triphenylphosphine (TPP) to triphenylphosphine oxide (TPPO) when reacted with hydroperoxides. A partial-leastsquares calibration was developed for 8 mm o.d. vials by preparing randomized mixtures of TPP and TPPO in a zero-PV oil. The method was validated with samples prepared by gravimetric dilution of oxidized oil with a zero-PV oil. It was shown that the American Oil Chemists’ Society primary reference method was quite reproducible (±0.5 PV), but relatively insensitive to PV differences at lower (0–2) PV. The FT-NIR method on the other hand was shown to be more accurate overall in tracking PV, but slightly less reproducible (0.9 PV) due to working close to the limit of detection. The sensitivity and reproducibility of the FT-NIR method could be improved upon through the use of larger-diameter vials combined with a detector having a wider dynamic range. The proposed FT-NIR PV method is simple to calibrate and implement and can be automated to allow for routine quality control analysis of edible fats and oils.
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