This work reports a new approach to extract the maximum chemical information from the absorption spectrum of extra virgin olive oils (EVOOs) in the 390-720 nm spectral range, where "oil pigments" dominate the light absorption. Four most important pigments, i.e., two carotenoids (lutein and β-carotene) and two chlorophylls (pheophytin-a and pheophytin-b), are chosen as reference oil pigments, being present in all the reported analytical data regarding pigments of EVOOs. The method allows the quantification of the concentration values of these four pigments directly from the deconvolution of the measured absorption spectrum of EVOOs. Advantages and limits of the method and the reliability of the pigment family quantification are discussed. The main point of this work is the description of a fast and simple method to extract of such information in less than a minute, through the mathematical analysis of the UV-vis spectrum of untreated samples of oil.
The interest in development
of new non-destructive methods for
characterization of extra virgin olive oils (EVOOs) has been increasing
in the recent years. Among different experimental techniques, nuclear
magnetic resonance (NMR) relaxation measurements are very promising
in the field of food characterization and authentication. In this
study, we focused on relaxation times T
1 and T
2 measured at different magnetic
field strengths (namely, 2, 100, and 400 MHz) and 1H NMR T
1 relaxometry dispersions directly on olive
oil samples without any chemical/physical treatments. A large set
of EVOO samples produced in two regions of Italy, Tuscany and Apulia,
were investigated by means of 1H NMR relaxation techniques.
The relaxation studies reported here show several common features
between the two sets of EVOO samples, thus indicating that relaxation
properties, namely, the ranges of values of T
1 and T
2 at 2 and 100 MHz, are
characteristic of EVOOs, independently from the cultivars, climate,
and geographic origin. This is a promising result in view of quality
control and monitoring.
Olive oils and, in
particular, extra-virgin olive oils (EVOOs)
are one of the most frauded food. Among the different adulterations
of EVOOs, the mixture of high-quality olive oils with vegetable oils
is one of the most common in the market. The need for fast and cheap
techniques able to detect extra-virgin olive oil adulterations was
the main motivation for the present research work based on 1H NMR relaxation and diffusion measurements. In particular, the 1H NMR relaxation times, T
1 and T
2, measured at 2 and 100 MHz on about 60 EVOO
samples produced in Italy are compared with those measured on four
different vegetable oils, produced from macadamia nuts, linseeds,
sunflower seeds, and soybeans. Self-diffusion coefficients on this
set of olive oils and vegetable oil samples were measured by means
of the 1H NMR diffusion ordered spectroscopy (DOSY) technique,
showing that, except for the macadamia oil, other vegetable oils are
characterized by an average diffusion coefficient sensibly different
from extra-virgin olive oils. Preliminary tests based on both NMR
relaxation and diffusometry methods indicate that eventual adulterations
of EVOO with linseed oil and macadamia oil are the easiest and the
most difficult frauds to be detected, respectively.
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