Reliability of the bromthymol blue method for color in virgin olive oils

Moyano, Marı́a José; Melgosa, Manuel; Alba, J.; Hita, E.; Heredia, Francisco J.

doi:10.1007/s11746-999-0160-x

Cited by 20 publications

(19 citation statements)

References 12 publications

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“…The corresponding BTB index (pH-concentration) is indicated together with each standard. Note that the characteristic triangular distribution of the BTB standards in the a*,b* plane from spectrophotometric measurements (15) disappears when the spectroradiometric measurements are used. A comparable result is found when considering the third dimension L* of the CIELAB space (i.e., using the representations in the a*,L* or b*,L* plane).…”

Section: Resultsmentioning

confidence: 99%

“…The temporal degradation of color in different materials is a known fact (13,14), which can also be assumed in the case of the BTB standards. In fact, it is recommended (7) that the color of the BTB standards be tested every 6 mon by comparison with recently prepared solutions, and significant color variations have been reported after a 2-yr period for a set of BTB standards (15). If the changes in color are real, then the loss of color fastness of the BTB standards may imply that, for rigorous specification of the oil color, the period of use of these standards should be limited to an appropriate time interval.…”

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Reproducibility of the bromthymol blue standards used for color specification of virgin olive oil

Melgosa

Prez

Hita

et al. 2001

J Americ Oil Chem Soc

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Three replicates were prepared for each of 60 BTB (bromthymol blue) standards, which are usually employed to determine the color of virgin olive and seed oils, and their colors were measured by spectrophotometric and spectroradiometric techniques on a monthly basis over a year. Although in principle both techniques are valid, their results are weakly correlated. The major color change of the BTB standards occurred soon after sample preparation; after 5 mon, the color stabilized at approximately 3.0 Commission Internationale de l'Éclairage 1976-(L*a*b*) (CIELAB) units, with respect to the initial values. Therefore, after preparation, a certain waiting period would be advisable before using the BTB standards. The color of the BTB standards changes over time in the sense of becoming lighter, more saturated, and less greenish. In the monthly periods after the fifth month, the average color change of the BTB standards was negligible, being slightly lower than the average variability of the three replicates (which is around 1.5 CIELAB units).Paper no. J9707 in JAOCS 78, 265-270 (March 2001). KEY WORDS:Bromthymol blue method, BTB method, CIELAB, color differences, color fastness, color of virgin olive oils, color reproducibility, oil-color measurement.FIG. 6. Temporal evolution of the color of BTB standard 5-5 over a year, according to spectroradiometric measurements. The CIELAB planes C*,L* (A) and h,L* (B) are distinguished; in each, the numbers 0-12 indicate the number of months since the preparation of the standard. The error bars centered in the initial and final measurements (0 and 12) indicate the standard deviation corresponding to the measurements of the three replicates of this BTB standard at these times.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Reproducibility of the bromthymol blue standards used for color specification of virgin olive oil

Melgosa

Prez

Hita

et al. 2001

J Americ Oil Chem Soc

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“…This is a long and tedious procedure that lacks accuracy and shows some deficiencies when characterizing olive oil colors because of metamerism (9) and visual variability among observers. The accuracy, reliability, and reproducibility of this method has already been discussed (10)(11)(12). Similar problems arise when oil color is measured by means of visual or automatic colorimeters, mainly when green tonalities are present (13), which indicates that any method based on comparisons with standards shows an inherent error owing to the subjectivity of visual impressions.…”

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confidence: 87%

“…In particular, the CIELAB system has been accepted worldwide in most industries. Its application to virgin olive oil samples provides better results than those obtained by visual methods (10).…”

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Chromatic evolution of virgin olive oils submitted to an accelerated oxidation test

Ceballos

Moyano

Vicario

et al. 2003

J Americ Oil Chem Soc

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Six samples of virgin olive oil obtained from several varieties of olive fruits (Picual, Manzanilla, Lechín, and Arbequina) were submitted to an accelerated oxidation process during a 63-h period under the conditions of the oil stability index (OSI), as measured by a Rancimat (100ºC) apparatus. Spectra were measured every 3 h, and chlorophyll and carotenoid indexes and CIELAB color ordinates were calculated. As oxidation time increased, remarkable changes in the spectral characteristics and color ordinates were observed. Oxidation provoked less vivid colors (lower values for chroma, C* ab ) in all the samples; however, only some varieties became darker (lower values for lightness, L*). The pigment loss calculated for oxidized oils was 67% for the carotenoid index and 58% for the chlorophyll index. Mathematical models are offered to predict color changes with time of storage at 20ºC.

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“…Este método es un procedimiento para especificar el color del aceite de oliva y aceites de semilla mediante comparaciones visuales entre la muestra de aceite y un conjunto de soluciones estándar distribuidas en una escala bidimensional de color de 6 x 10 = 60 muestras. Recientes trabajos (Melgosa et al, 2000;Moyano et al, 1999) señalan la baja precisión y exactitud de este método y sugieren el uso del espacio de color CIE-1976 (L*,a*,b*) (CIELAB) como más apropiado para la especificación del color y proponen una relación numérica entre los índices ABT y las coordenadas CIELAB.…”

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Colorimetric characterization and classification of the virgin olive oil from the spanish-moroccan mediterranean area

Pérez¹,

Yebra²,

Melgosa³

et al. 2003

Grasas y Aceites

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RESUMENCaracterización colorimétrica y clasificación del aceite de oliva virgen de la cuenca mediterránea hispanomarroquí.Se han realizado medidas por reflexión del color de 200 muestras de aceite de oliva virgen de las zonas de producción sur de España y zona norte de Marruecos. También se han realizado medidas del grado de acidez de los mismos y se emplea el análi-sis cluster para el estudio de su clasificación. Los resultados obtenidos muestran que, en general, los aceites marroquíes presentan con respecto a los españoles, tonalidades más verdosas (h o medio de 87,3 o frente a 85,1 o ) y son menos saturados (C* medio de 91,7 frente a 105,3). Por otra parte, el grado de acidez difiere notablemente para ambas zonas geográficas, con valores medios de 0,31 para los aceites españoles y 2,87 para los marroquíes. A partir de estas medidas experimentales el análisis cluster muestra que, es posible clasificar los aceites de oliva según su zona geográfica de producción (hispano-marroquí), en función del grado de acidez ó del ángulo de tono. , and those are less saturated (C* average of 91.7 and 105.3, respectively). On the other hand, acidity is remarkably different for these two geographic zones, having average values of 0.31 for Spanish oils and 2.87 for Moroccan ones. From these experimental measurements, the cluster analysis shows that it is possible to classify these oils according to their geographic production zones (Spanish-Moroccan area) depending on the acidity or the hue angle. PALABRAS-CLAVE: Aceite de oliva --Acidez --Áreas de producción -Color. SUMMARY KEY-WORDS: Acidity --Colour --Olive oil --Production areas.

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Reliability of the bromthymol blue method for color in virgin olive oils

Cited by 20 publications

References 12 publications

Reproducibility of the bromthymol blue standards used for color specification of virgin olive oil

Reproducibility of the bromthymol blue standards used for color specification of virgin olive oil

Chromatic evolution of virgin olive oils submitted to an accelerated oxidation test

Colorimetric characterization and classification of the virgin olive oil from the spanish-moroccan mediterranean area

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