A.I. Negueruela

Note. Visual and Instrumental Color Evaluation in Red Wines

The color of 15 red wines from several wineries within the renowned wine-producing region Rioja (Northern Spain) was measured by spectrophotometric and spectroradiometric techniques and was visually assessed in a pair-comparison experiment by a panel of 10 experienced observers having normal color vision. Correlation between instrumental color measurements made by spectrophotometric and spectroradiometric techniques was very low, as expected from major differences in the experimental conditions employed (different illumination, path lengths and glass effects). Spectroradiometric measurements at the center of the wine sampler and at positions displaced 1 cm in the horizontal and vertical directions were quite different, mainly because of an increase of the lightness L*, the average color differences between them being high (3.5 and 2.6 CIELAB units, respectively). A 50% acceptance percentage resulted for a color difference of 2.8 CIELAB units, using a reference anchor-pair of wine samples with 4.0 CIELAB units. Thus, a value around 3.0 CIELAB units should be considered a preliminary estimate of the acceptable tolerance by the human eye for red wines poured in standard wine samplers.

Beef colour evolution as a function of ultimate pH.

Colour in CIELAB space was assessed in 31 yearling entire male cattle from their reflectance spectra (400-700 nm) at six different times (0 min, 15 min, 5 h, 48 h, 6 days and 9 days). Cluster analysis applied to all the colour co-ordinates divided the samples into two groups according to their ultimate pH (pHu): pH<6.1 and pH⩾6.1. pH ranged between 5.17 and 7.10. Colour development in pH⩾6.1 group was less visually appreciable than in pH<6.1 group. This difference was also observed in the reflectance spectra. The application of discriminant analysis to these groups established that b* and h* CIELAB co-ordinates are the most discriminant variables. Meat pigment evolution was assessed by the spectrophotometric indexes. R (∞)(632)- R (∞)(614); K S (614)- K S (632) and the K S (630)- K S (580) indexes were found to be the most significant to represent the difference between the two groups.

Use of three tristimulus values from surface reflectance spectra to calculate the principal components for reconstructing these spectra by using only three eigenvectors

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.

The influence of final conditions on meat colour in light lamb carcasses.

Tristimulus values (X, Y, Z) and CIELAB colourimetric coordinates have been measured in m. Longissimus dorsi and m. Triceps braquialis caput longum muscles in 86 light carcasses of lambs from different origins. By applying to these data different mathematical methods (ANOVA, Discriminant Analysis, Principal Components Analysis and Cluster Analysis) we have obtained a good classification of these animals in groups, which has been established according to the different final conditions (feeding or storage). In this way, the percentage of animals accurately classified into their group is 94.2%. Worse results were obtained (84.9%) if the animals were grouped taking their breed or/and origin as a reference.

A novel and enhanced approach for the assessment of the total carotenoid content of foods based on multipoint spectroscopic measurements.

We have devised a more sensible approach to estimate the carotenoid content of orange juices, which can be regarded as a model system of food with intricate carotenoid pattern. For this purpose spectroscopic information at several wavelengths and spectra of the juices and not from their carotenoid extracts were considered, such that more accurate and rapid quantitative assessments can be achieved. The wavelengths proposed on the basis of the characteristic vector method were 420, 455, 515, 545 and 610nm or 420, 445, 510, 545 and 605nm, depending on the measurement conditions. The correlations between the carotenoid content and the reflectances at these wavelengths were very good (R=0.94 and 0.90, respectively). Additionally, it was demonstrated that the colour of the juices could be assessed with very good accuracy considering them. Due to its simplicity and rapidity, this method is intended to facilitate the quality control of the carotenoid content of foodstuffs in the industry and/or in the field.

Monitoring Colour Evolution During Maturity in Fuji Apples

Colour changes in Fuji apples were monitored several days after full blooming (DAFB). Fruits were harvested at this commercial maturity (139 DAFB), 132, 146 and 153 DAFB. A new method was developed to determine the average colour of the apples by measuring the reflection spectra around the fruit to obtain a spectra weighted by the red and green areas. According to the evolution of the reflectance spectra during maturity, the proportion of chlorophyll decreased with regard to other pigments but it did not disappear. The colour obtained of those average spectra allowed a good classification of the apples according to ripeness. Values of the a * colour coordinate were well correlated to the visual evaluation of the colour assessed by a sensory trained panel, which could be used as a maturation index to optimize the marketing.

A proposal for a method to measure the colour of red wines by measuring transmittance at three wavelengths / Propuesta de un método de medida del color de vinos tintos mediante la lectura de las transmitancia a tres longitudes de onda

Characteristic vectors analysis has been used to reconstitute the transmittance spectrum of red wines measured in 0.2 cm path-length cells. We have verified that an accurate reconstitution of the spectrum is obtained with the mean vector and the first three characteristic vectors. Applying the outputs obtained to the colour calculation, tristimulus values are obtained as a function of transmittance measured at 420, 520 and 620 nm. The errors involved, measured in colour differ ences, are less than 3 CIELAB units in 97% of the cases.

Colorimetry in Port wines / Colorimetría de vinos de Oporto:

This paper sets out to establish a methodology for measuring the colour of Port wines that complies with both the EU Regulation and the Office Internationale de la Vigne et du Vin (OIV) guidelines using the simplest possible approach. Fifty six Port wines of various types have been utilized, namely Brancos, Aloirados, Tintos and Retintos. In order to determine the influence of the spec tral interval on the results, the colour coordinates have been calculated using spectral measure ments every 1, 5 and 10 nm. The colour differences between them were lower than 0.5 CIELAB units and, therefore the use of a spectral interval of 10 nm is sufficient, as the CIE recommends. Absorbance spectra were recorded with 2, 5 and 10 nm pathlength cells to test the validity of Beers law for Port Wines. In general, they comply quite well with that law, but some precision problems arise in the measurements, in relation to the pathlength of the cell. We conclude that the best measurements are obtained with 2 mm pathlength cells for Tintos and Retintos Port wines, and with 10 mm pathlength cells for Aloirados and Brancos Port wines.