Optical path length and wavelength selection using Vis / NIR 1 spectroscopy for olive oil ’ s free acidity determination

Four different optical path lengths, namely 0.5, 1, 5 and 10 mm, were assayed for 8 olive oil’s free acidity determination using Vis/NIR spectroscopy. Results illustrated 9 that the use of higher path length during spectra acquisition resulted in more accurate 10 PLS models, especially when using solely the NIR region. The PLS model obtained 11 with the NIR spectrum using the 10 mm cuvette was subjected to optimization by 12 Monte Carlo uninformative variable elimination (MCUVE) and successive projections 13 algorithm (SPA). Both methods drastically reduced the number of spectral variables and 14 markedly improved the performance of the PLS model, especially the SPA-PLS model, 15 which achieved a SEP (0.051) quite close to SEL (0.048). Interestingly, only 12 of the 16 85 spectral variables selected by SPA were among the 314 variables provided by 17 MCUVE. All in all, NIRS incorporated to MCUVE-PLS or SPA-PLS may be applied as 18 an alternative method for the rapid determination of olive oil’s free acidity. 19