Lipids. 2015 Jul;50(7):705-18. doi: 10.1007/s11745-015-4038-4. Epub 2015 Jun 7.
Abstract
A
new, rapid Fourier transform near infrared (FT-NIR) spectroscopic
procedure is described to screen for the authenticity of extra virgin
olive oils (EVOO) and to determine the kind and amount of an adulterant
in EVOO. To screen EVOO, a partial least squares (PLS1) calibration
model was developed to estimate a newly created FT-NIR index based
mainly on the relative intensities of two unique carbonyl overtone
absorptions in the FT-NIR spectra of EVOO and other mixtures attributed
to volatile (5280 cm(-1)) and non-volatile (5180 cm(-1)) components.
Spectra were also used to predict the fatty acid (FA) composition of
EVOO or samples spiked with an adulterant using previously developed
PLS1 calibration models. Some adulterated mixtures could be identified
provided the FA profile was sufficiently different from those of EVOO.
To identify the type and determine the quantity of an adulterant,
gravimetric mixtures were prepared by spiking EVOO with different
concentrations of each adulterant. Based on FT-NIR spectra, four PLS1
calibration models were developed for four specific groups of adulterants,
each with a characteristic FA composition. Using these different PLS1
calibration models for prediction, plots of predicted vs. gravimetric
concentrations of an adulterant in EVOO yielded linear regression
functions with four unique sets of slopes, one for each group of adulterants.
Four corresponding slope rules were defined that allowed for the
determination of the nature and concentration of an adulterant in EVOO
products by applying these four calibration models. The standard
addition technique was used for confirmation.
