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B. Muik, B. Lendl, A Molina-Diaz, M.J. Ayora-Cañada:
"Direct, reagent-free determination of free fatty acid content in olive oil and olives by Fourier transform Raman spectrometry";
Analytica Chimica Acta, 487 (2003), S. 211 - 220.

Fourier transform (FT) Raman spectrometry in combination with partial least squares (PLS) regression was used for direct,
reagent-free determination of free fatty acid (FFA) content in olive oils and olives. Oils were directly investigated in a simple
flow cell. Milled olives were measured in a dedicated sample cup, which was rotated eccentrically to the horizontal laser
beam during spectrum acquisition in order to compensate sample heterogeneity. Both external and internal (leave-one-out)
validation were used to assess the predictive ability of the PLS calibration models for FFA content (in terms of oleic acid) in
oil and olives in the range 0.20-6.14 and 0.15-3.79%, respectively. The root mean square error of prediction (RMSEP) was
0.29% for oil and 0.28% for olives. The predicted FFA contents were used to classify oils and olives in different categories
according to the European Union regulations. Ninety percent of the oil samples and 80% of the olives were correctly classified.
These results demonstrate that the proposed procedures can be used for screening of good quality olives before processing,
as well as, for the on-line control of the produced oil.

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