Monitoring PV in corn and soybean oils by NIR spectroscopy

Abstract

NIR spectroscopy was used successfully in our laboratory to monitor oxidation levels in vegetable oils. Calibration models were developed to measure PV in both soy and corn oils, using partial least squares (PLS) regression and forward stepwise multiple linear regression, from NIR transmission spectra. PV can be measured successfully in both corn and soy oils using a single calibration. The most successful calibration was based on PLS regression of first derivative spectra. When this calibration was applied to validation sample sets containing equal numbers of corn and soy oil samples, with PV ranging from 0 to 20 meq/kg, a correlation coefficient of 0.99 between titration and NIR values was obtained, with a standard error of prediction equal to 0.72 meq/kg. For both types of oil, changes occurred in the 2068 nm region of the NIR spectra as oxidation levels increased. These changes appear to be associated with the formation of hydroperoxides during oxidation of the oils.Existing analytical procedures for measuring the oxidation level in vegetable oils are time consuming, destructive to the sample, and costly, and they require large amounts of glassware, lipids, and potentially hazardous reagents. NIR spectroscopy, which can overcome many of these drawbacks, has many applications in the food industry, including fat and oil quality evaluation. In the recent past, a number of new spectroscopic methods have been developed for measuring lipid oxidation (1-5). These methods are simple, fast, and safe, and they dramatically reduce the labor and solvent needed. Previous work in our laboratory demonstrated that soybean oil oxidation, expressed as PV, can be determined successfully using NIR transmission spectroscopy as an alternative to the official AOCS iodometric titration method, and satisfactory repeatability was obtained by both methods (6).In the present study, NIR spectroscopy was examined as a possible alternative to the conventional titration method for determining oxidation levels in corn oils, and calibrations were developed for quantitative determination of PV of corn oils. Additionally, the potential of using a single calibration to measure oxidation in oils from multiple sources was evaluated. Therefore, the objectives of the present research were threefold: (i) to investigate the relationship between NIR spectra and lipid oxidation in corn oil; (ii) to evaluate the success of the NIR models developed by testing each with an independent set of corn oil samples; and (iii) to create and evaluate calibrations encompassing both soybean oil and corn oil. EXPERIMENTAL PROCEDURES Selection of corn oil samples. Commercial corn oils (CO)were used for calibration development and validation. To achieve variation in the oils, five CO representing four commercial brands with different "sell by" dates and batch codes were purchased from local supermarkets in Lincoln, Nebraska. Samples with a range of oxidation levels as measured by PV were then prepared by subjecting each corn oil to fluorescent light for varying lengths ...

Near infrared spectroscopy for on/in-line monitoring of quality in foods and beverages: A review

“…However, as opposed to PV and CD, measurement of AV by NIR was not as well as expected. Thereafter, they (Yildiz et al, 2002) determined PV in corn and soybean oils by NIR spectroscopy technique. When the calibration models developed by PLS regression of first derivative spectra were used to predict validation sets containing equal numbers of corn and soybean oil samples, good results were obtained.…”

NIR spectrometric determination of quality parameters in vegetable oils using iPLS and variable selection

“…However, the determination of anisidine value was less successful. That work was later extended to encompass NIR determination of peroxide value in both soybean and corn oil samples using a single PLS model (Yildiz, Wehling, & Cuppett, 2002). Again, good results were obtained with a correlation coefficient of 0.99 between NIR-PLS determinations and reference titration values.…”

Near‐infrared spectroscopy for the determination of lipid oxidation in cereal food products

“…For example, Van de Voort et al [2] published the first Fourier transform spectroscopy method for PV determination based on the characteristic OH stretching absorption band of peroxides in the middle IR (mid-IR). The possibility to use near-infrared (NIR) spectroscopy to determine PV was investigated on crude palm [3], corn and soybean oils [4], or rapeseed lubricant derivatives [5]. Other examples of IR spectroscopy methods concern the measurement of oxidative adulteration of oils and fats and the determination of thiobarbituric acid-reactive substances [6,7] or anisidine values (AV) [8,9].…”