Using optical NIR sensor for on-line virgin olive oils characterization

Near-infrared transmittance spectroscopy was applied to on-line control quality and characterization of virgin olive oils. The transmittance spectrum (log 1/T) was obtained through dispersal equipment, scanning the samples between 750 and 2500. A 1 mm optical path length flow cell and holding 120 mu l was employed. Calibration models for: acidity value (AV), bitter taste (k225) and fatty acid composition (FAME), were previously developed in the laboratory using partial least squares (PLS) regression. A total of 190 virgin olive oil samples, gathered during the usual harvesting time of three olive crop seasons, were used. The validation set gave correlation coefficients and standard error of prediction of 0.999 and 0.35, 0.936 and 0.058, 0.998 and 0.604, 0.992 and 0.674% for AV, k225, fatty acid oleic and fatty acid linoleic, respectively. These PLS models, prior to a slope/bias correction, were used to monitor on-line values of these parameters during the processing of virgin olive oils in real olive mills. Samples of oils were obtained for chemical analysis. Application of NIR transmittance spectroscopy on-line to virgin olive oil production line, has allowed to detect, at real-time, the changes produced in the characteristics of the oils during their production. The results indicate similarity between information both NIR and reference laboratory methods. (c) 2005 Elsevier B.V. All rights reserved.