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

The bromthymol blue (BTB) method is currently used for the assessment of co lor in olive and seed oils by visual comparison with standard solutions. Tw o BTB scales were prepared with 2 yr difference and compared, and the recen t one was used to analyze 502 virgin olive oil samples, obtained by the Abe ncor(R) technique reproducing the industrial procedure. The temporal chroma tic degradation of the BTB samples after 2 yr [3.93 Commission internationa le de l'Eclairage (CIE) 1976-(L*a*b*) (CIELAB) units, on the average], as w ell 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 tole rance of 1.52 CIELAB units), indicates the limitations of the BTB method. L inear regression models are proposed in order to compute with acceptable ac curacy the BTB indices from chromaticparameters. The use of CIELAB for the specification and future studies on color in virgin olive oils is recommend ed.