Journal of the American Oil Chemists' Society

, Volume 77, Issue 10, pp 1093–1100

Precision and accuracy in the color specification of virgin olive oils from the bromthymol blue method

  • M. Melgosa
  • M. M. Prez
  • E. Hita
  • M. J. Moyano
  • J. Alba
  • F. J. Heredia
Article

DOI: 10.1007/s11746-000-0172-8

Cite this article as:
Melgosa, M., Prez, M.M., Hita, E. et al. J Amer Oil Chem Soc (2000) 77: 1093. doi:10.1007/s11746-000-0172-8

Abstract

Twenty experienced observers with nondefective color vision judged 27 virgin olive oil samples within an acceptable color range, using the bromthymol blue (BTB) method, under controlled observation conditions (daylight source with a correlated color temperature of 6500 K, and standard gray back-ground). On the average, 44.8% of the observers agreed in their selections of the BTB standard solution matching a given oil sample, and this percentage increased to 88.2% considering ±one step in the two dimensions (pH and concentration) of the BTB scale. On the average, the lowest color difference between oil samples and available BTB solutions was 6.6 Commission Internationale de l'Éclairage 1976-(L*a*b*) (CIELAB) units, but this color difference was approximately two times greater for the color difference between oil samples and BTB solutions selected by our observers. The colors of the BTB standard solutions in the CIELAB space are not uniformly distributed, and thus one step in pH or concentration is equivalent to CIELAB color differences varying in a wide range (1.7–13.5 and 1.7–26.3 CIELAB units, respectively). From these values, indicating low precision, accuracy, and uniformity, some suggestions are made for future improvements of the current BTB method.

Key Words

Bromthymol blue method CIELAB color differences oil color virgin olive oils visual judgments 

Copyright information

© AOCS Press 2000

Authors and Affiliations

  • M. Melgosa
    • 1
  • M. M. Prez
    • 1
  • E. Hita
    • 1
  • M. J. Moyano
    • 2
  • J. Alba
    • 2
  • F. J. Heredia
    • 3
  1. 1.Departamento de Óptica, Facultad de CienciasUniversidad de GranadaGranadaSpain
  2. 2.Almazara Experimental del Instituto de la GrasaCSICSevillaSpain
  3. 3.Área de Nutrición y Bromatología, Facultad de FarmaciaUniversidad de SevillaSevillaSpain

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