Analytical Sciences

The Detection and Quantification of Adulteration in Olive Oil by Near-Infrared Spectroscopy and Chemometrics

Alfred A. CHRISTY,* Sumaporn KASEMSUMRAN,** Yiping DU,** and Yukihiro OZAKI**

*Department of Chemistry, Agder University College, Serviceboks 422, N-4604 Kristiansand, Norway
**Department of Chemistry, Research Center for Near-Infrared Spectroscopy, School of Science & Technology, Kwansei-Gakuin University, Sanda 669-1337, Japan

A new procedure has been developed for the classification and quantification of the adulteration of pure olive oil by soya oil, sun flower oil, corn oil, walnut oil and hazelnut oil. The study was based on a chemometric analysis of the nearinfrared (NIR) spectra of olive-oil mixtures containing different adulterants. The adulteration of olive oil was carefully carried out gravimetrically in a 4 mm quartz cuvette, starting with pure olive oil in the cuvette first. NIR spectra of the 525 adulterated mixtures were measured in the region of 12000 - 4000 cm^-1. The spectra were subjected batch wise to multiplicative signal correction (MSC) before calculating the principal component (PCA) models. The MSC-corrected data were subjected to Savitzky-Golay smoothing and a mean normalization procedure before developing partial leastsquares calibration (PLS) models. The results revealed that the models predicted the adulterants, corn oil, sun flower oil, soya oil, walnut oil and hazelnut oil involved in olive oil with error limits ±0.57, ±1.32, ±0.96, ±0.56 and ±0.57% weight/weight, respectively. Furthermore, the PCA developed models were able to classify unknown adulterated olive oil mixtures with almost 100% certainty. Quantification of the adulterants was carried out using their respective PLS models within the same error limits as mentioned above.

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