F. Ayala, J. F. Echávarri, and A. I. Negueruela
A
new method for calculating the color coordinates of
red and rosé wines is presented. Characteristic vector analysis
has been applied to the transmittance spectra of 690 wines. This
method allows the reconstitution of the transmittance spectra of all
the wines used from the mean vector and three characteristic vectors.
Expressions for tristimulus values are obtained as function of
transmittance measurements at three wavelengths. The color of each wine has been calculated based on these
results. Color differences between these
results and those obtained by application of the CIE method to
experimentally measured spectra are smaller than differences between
the results obtained making use of the recommended OIV method and the aforementioned CIE method.
F. Ayala, J. F. Echávarri, and A. I. Negueruela
This
paper studies a new method to calculate color
coordinates of white wines and brandies. Transmittance spectra of
350 samples have been subjected to characteristic vectors analysis.
This method enables us to reconstitute the transmittance spectra
of the whole set of wines from the mean vector and three characteristic
vectors. Expressions for the tristimulus values are derived from
these results as functions of the transmittance values measured at
440, 540, and 610 nm. Color of each wine was
calculated from the tristimulus values. The results obtained are
better than results obtained by means of the OIV
method in comparison with the 40 measurements CIE method.
F. Ayala, J. F. Echávarri, and A. I. Negueruela
A
simplified method to calculate color coordinates of any red, rosé,
or white wine or any brandy is studied in this paper. As in the
previous papers, this method makes possible the reconstitution of
the transmittance spectrum of any wine or brandy from a mean vector
and three characteristic vectors, and expressions for the
tristimulus values can be obtained as functions of transmittance values
at only three wavelengths, 440,530, and 600 nm. The color of each
wine and brandy is calculated from these tristimulus values. Spectra
of 1614 wines and brandies have been used in characteristic vector
analysis, 959 in statistical calculations, and 655 for verifying the
results. These results are similar than those obtained in Parts I
and II.
Influence of measuring interval on calculation of
the colour coordinates of wine
J. F. Echávarri, F. Ayala, and A. I. Negueruela
According to the data capture capacity
of measuring apparatuses, the determining of colorimetric parameters can be carried out with differing
measure spaces. It would therefore
appear to be necessary to understand how this effects the results.
The CIE recommends conducting colorimetric calculations with an interval Dl of 1 nm on a measuring field going from 360 to 830 nm but specifies that, in most practical cases, an interval
of 380-780 nm and a measuring
space of 5 nm are acceptable.
The colorimetric coordinates of wine are compared in this paper calculated
between 380 and 780 nm, the field of most spectrophotometers, and between 400 and
700 nm
the field
which is
used by
several spectrocolorimeters.
The measure spaces are: 1, 2, 5, 10 and 20 nm.
The results obtained are
similar in all cases.
Simplified measurement of virgin
olive oil color by application of the characteristic vector method.
Moyano, MŞ J., Ayala, F., Echávarri,
J.F., Alba, J., Negueruela,
A.I. and Heredia, F.J.
There
are several simplified methods to measure the color of virgin olive oils.
However, their reliability is questionable as they provide errors, that
sometimes can be considerable. With the aim of overcoming these objections, a
new method to calculate colour coordinates and objective chromatic parameters
in the colour region of these olive oils is proposed. The method is a
simplification of the original method proposed by the Commission International
de l’Eclairage, based on the measurement of the
complete visible spectrum, from 380 to 770 nm. New equations to calculate
tristimulus values as functions of these transmittance values are proposed
based on an acute reconstruction of oil transmission spectra from measurements
at 3 to 6 wavelengths, provided by the characteristic vector analysis. The
results show that colour differences, between the colour coordinates of the
experimental samples and those obtained by means of proposed method, are
smaller than three CIELAB units for more than ninety percent of the samples,
when equations based in four or more wavelengths are used.
Influence of packaging
films on microbiological and sensorial evolution of minimally processed borage
(borago officinalis)
Giménez M., C. Olarte, S. Sanz,
C. Lomas, J.F. Echávarri,
F. Ayala
The atmospheres prevalent in borage packaged in 5
different films, together with different water-vapor permeabilities of the films, determined the evolution of
the visual and microbiological quality of borage. PVC films proved inadequate
to extend the sensory quality since the samples packaged with the films were
spoiled on day 9, whereas among the P-Plus films, the least permeable film was
the most adequate to extend the sensory quality of borage until day 15. For
most of the treatments, no correlation between the microbial growth and changes
in appearance was found. Thus, some treatments with a fair sensory evaluation
had microbial counts higher than those allowed by the European legislation.
Relation between spoilage and microbiological quality in minimally
processed artichoke packaged with different films
The atmospheres obtained, together with the different permeability to water vapor of the films under study, determined the evolution of
the visual and microbiological quality of the artichoke.
For
most of the batches, no correspondence was found between microbial growth and
changes in appearance. Those batches where the equilibrium atmosphere was
clearly anaerobic showed microbial counts below the legally established
microbiological limits but also showed a rapid loss of sensory quality. On the
other hand, some batches with an acceptable sensory evaluation had microbial
counts higher than those allowed by the legislation. This last situation is
particularly dangerous from a health point of view since it allows the growth
of micro-organisms (even pathogens) although the product may seem to be
acceptable for consumption.
This
lack of correspondence constitutes an important point to be attended to on the
microbiological safety of these foods, since the preservation technologies
applied allow the prolonging of their sensory characteristics but, at the same
time, may favour the growth of micro-organisms.
Valentín Pérez-Caballero, Fernando Ayala, J. Federico Echávarri, and Angel I. Negueruela
Recent
work on simplified methods to determine chromatic characteristics of
wine uses transmittance measurements at three wavelengths, thus
improving the results of the Office International de la Vigne et du Vin
reference method compared to the CIE method. These simplified
methods still pose some problems for wines with a low lightness;
consequently, a simplified method that uses four wavelengths instead
of three is proposed. The errors in the determination of the
colorimetric coordinates are less than 2.5 CIELAB units of color
difference in 1840 samples from the 1841 wines and brandies under
study. This method is proposed as a substitute for the current OIV method for the determination of the
chromatic characteristics of wine, which has been under review since
1992.
S. Sanz, F. Ayala, C. Olarte, J.F.
Echávarri, M. Giménez
The
atmosphere surrounding minimally processed vegetables is extremely important to
extend their shelf life, and one of the most influential factors on its
composition is the permeability of the film used in the packaging. This study
determined the impact of the preservation technologies on sensory quality (color, and sensory acceptability). The atmospheres
obtained, together with the different permeability to water vapor
of the films under study, determined the evolution of the visual quality of the
artichoke.
The
division of Color Space into ten zones, corresponding
to the ten Munsell hues, allows a good reconstruction
of surface reflectance spectra using just three eigenvectors, obtained by
applying principal components analysis to the reflectance spectra of the Munsell Atlas specimens (model group), although the basis
vectors obtained are different for each subspace. The use of the tristimulus
values from each measured spectrum, calculated with the Illuminant D65 and the
Standard Observer CIE64 to obtain the principal components necessary to
reconstruct the spectrum, allows a very high degree of metamerism
to be attained between the two spectra (measured and reconstructed).
Furthermore, this method of calculating the principal components allows
reconstruction of the spectra of specimens from other sample sets that differ
from the model group used in the PCA. The
colorimetric accuracy obtained in the new sample sets is similar to that obtained
for the model group.
Evaluation of different varieties
of cauliflower for minimal processing
Susana Sanz, Carmen Olarte, J Federico Echávarri, Fernando Ayala
The
impact of minimal processing technology on the sensory quality and the growth
of micro-organisms in eight varieties of cauliflower packaged in four different
films (one PVC and three P-Plus) was measured and quantified during more than
25 days of storage at 4 °C. Other important parameters such as weight loss and
gas concentration in the packages were also determined. The composition of the
atmosphere in the packages of minimally processed cauliflower depended on both
the permeability of the film used for the packaging and the variety of
cauliflower. When establishing shelf-life, loss of sensory quality was the
deciding factor rather than loss of microbiological quality. The initial
microbial load proved more important than the composition of the atmosphere
inside the packages. In sensory evaluation the most important aspect was
colour. In instrumental evaluation, coordinate b* was the main means of
estimating shelf-life. The combination of P-Plus 120 film and varieties of
cauliflower of large size and great vigour allowed the atmosphere inside the
packages to have an O2 level below 10% and a CO2 level
above 10%. That atmosphere composition proved essential for maintaining the
sensory quality of minimally processed cauliflower. In these conditions,
samples attained a shelf-life of more than 25 days. However, the different
behaviours of the cauliflower varieties make it necessary to establish
particular packaging conditions. The use of less permeable films than those
used in this study, or the use of actively modified atmospheres, could be an
alternative for those varieties that require special packaging conditions when
processed using this technology.
Simplified method for calculating colour of honey by application of the characteristic
vector method
M. Lourdes González-Miret,
Fernando Ayala, Anass Terrab,
J. Federico Echávarri, A. Ignacio Negueruela
and Francisco J. Heredia
A quick and
simple method to obtain the colour of honeys with minimum error is proposed. Characteristic
vector analysis has been tested and proved to be applicable to the
reconstruction of honey reflectance spectra. Expressions for tristimulus values
are obtained as function of reflectance measurements at a few wavelengths.
Different sets of reflectance were tested (from 3 to 6 wavelengths) showing
better results as the number of characteristic vectors (wavelengths) increases.
The measures were made both over white and over black backing. Results showed
that, when spectrophotometric measurements are made
with 10 mm pathlength cells, the determination
of reflectance at four wavelengths (443, 530, 554, and 618 nm for white
backing; 439, 488, 555 and 636 nm for black backing) is adequate to
reconstruct the spectrum and to obtain the tristimulus chromatic
characteristics. The black backing measurements showed better results, being
74% and 57% (black and white backing measurements, respectively) the percentage
of samples giving colour differences less than 1 CIELAB
unit between the calculated coordinates and those obtained from the whole
visible spectra.
Influence of
exposure to light on the sensorial quality of minimally processed cauliflower.
S. Sanz
Cervera, C. Olarte, J. F. Echávarri, F. Ayala
The
impact of lighting on minimally processed cauliflower packaged in 4 different
film types (PVC and 3 P-Plus) has been measured and quantified. The effect on
the sensorial quality of storage at 4 degrees C in darkness and partial or
continuous lighting was evaluated. The gas concentrations in the packages and
the weight losses were also determined. Atmosphere composition inside the
packages depended on both the permeability of the film used for the packaging
and exposure to light. Samples stored with lighting maintained the gaseous
exchange between plant tissue and the atmosphere inside the packages for longer
periods than in samples kept in darkness. This prompted a greater loss of water
vapor as well as the development of atmospheres with
low levels of O2 and high levels of CO2 in the samples packed with less
permeable films. The most important aspect in sensory evaluation was color. In instrumental color
evaluation, coordinates h* and L* were the main means for estimating color evolution. The presence of light accelerated browning
in the cut zones. The development of abnormal coloring
in these areas marked the end of shelf life for minimally processed
cauliflower. Among the sensory attributes studied, color
was the most affected by exposure to light. Samples packed in P-Plus 120 film
displayed the lowest level of color deterioration in
the cut zones. However, under lit conditions, the low permeability of this film
caused atmospheres with very low O2 contents and high CO2 contents. These
atmospheres produced a loss of texture and the development of off-odors.