Article

Journal of the American Oil Chemists' Society

, Volume 76, Issue 6, pp 687-692

First online:

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

  • M. J. MoyanoAffiliated withAlmazara Experimental del Instituto de la Grasa, CSIC
  • , M. MelgosaAffiliated withDepartamento de Óptica, Facultad de Ciencias, Universidad de Granada
  • , J. AlbaAffiliated withAlmazara Experimental del Instituto de la Grasa, CSIC
  • , E. HitaAffiliated withDepartamento de Óptica, Facultad de Ciencias, Universidad de Granada
  • , F. J. HerediaAffiliated withÁrea de Nutrición y Bromatología, Facultad de Farmacia, Universidad de Sevilla, c/P. García González s/n Email author 

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Abstract

The bromthymol blue (BTB) method is currently used for the assessment of color in olive and seed oils by visual comparison with standard solutions. Two BTB scales were prepared with 2 yr difference and compared, and the recent one was used to analyze 502 virgin olive oil samples, obtained by the Abencor® technique reproducing the industrial procedure. The temporal chromatic degradation of the BTB samples after 2 yr [3.93 Commission Internationale de l’Eclairage (CIE) 1976-(L*a*b*) (CIELAB) units, on the average], as well as the small percentage of virgin olive oils matching the colors of the samples provided by the BTB scales (13.1% with a suprathreshold color tolerance of 1.52 CIELAB units), indicates the limitations of the BTB method. Linear regression models are proposed in order to compute with acceptable accuracy the BTB indices from chromaticparameters. The use of CIELAB for the specification and future studies on color in virgin olive oils is recommended.

Key Words

Bromthymol blue method CIELAB color tristimulus colorimetry virgin olive oil