A group of scientists of the University of Granada, the University of Sevilla and the Fat Institute (CSIC) has proved the poor reliability of the current official method in Spain to measure the colour of virgin olive oil and has lied the foundations for a new and more accurate system which allows to use this parameter as an oil quality sign.
«Colour is a very important magnitude from the point of view business and industry because it is a sign of virgin olive oil quality (colour is connected with oil chemical features, like acidity, etc.) and it has a great deal of influence on consumers´ preferences. By using optical techniques, it is also possible to test, for example, if there are adulterations in oil in a fast and non-invasive way».
Researcher Manuel Melgosa Latorre, Professor of Optics in the University of Granada and secretary of the Colour Committee of the Spanish Optical Society, is one of the scientists who have studied colour in specific products like virgin olive oil or los wine: The research team deals with work lines like differences and similarities between Spanish and Maroccan olives; analysis of the preferences of colours and teenagers´personality; connection between colour and the edaphological properties of Mediterranean soils and automated evaluation of colour differences in different industrial implementations.
In the case of virgin olive oil, Melgosa Latorre states that the interest in measuring colour is a response to a technical and commercial request «to characterize the product properly». «We can not forget that the olive-oil sector moves about 500,000 million pesetas per campaign only in Andalusia. If we defend oil as a top quality product and we want to export it with guarantees, origin denominations (OD: Spanish prestigious product classification) should include colour as a characteristic and a quality sign», he asserts.
At the moment, the offical current method in Spain to measure virgin olive oil colour is called Method ABT (Bromothymol Blue Method). According to the researcher from Granada, this system was introduced in 1986 by R. Gutiérrez and F. Gutiérrez as a «Fast Method to Define the Virgon Olive Oil Colour» and it consists of 60 dissolutions which are used as comparative patterns, as a colour card. The analysis of this colour measuring system is one of the research lines of Melgosa Latorre´s group, whose results have been published in the Journal American Oil Chemists’ Society, a journal of international impact in 1999, 2000 and 2001.
In the first study, «Reliability of the Bromthymol Blue Method for Color in Virgin Olive Oils», the researchers reveal the poor reliability of the ABT Method since colour specifications refer to a different space from that recommended by the international community (CIELAB). «ABT patterns are not well distributed in the colour space; in addition, some virgin olive oils are not in the colour space area where ABT patterns position», the lecturer explains.
The second work («Precision and Accuracy in the Color Specification of Virgin Olive Oils from the Bromthymol Blue Method») confirm the lack of precision and accuracy of the system and proves that a review appropriate to the advances in the field of Optics is necessary.
The last research work (called «Reproducibility of the Bromthymol Blue Standards Used for Color Specification of Virgin Olive Oil») aimed to confirm if ABT patterns (disolutions) are or not temporarily stable. The scientists subjected the samples to periodical measurements for a year and they detected that disolutions were unstable immediately after their preparation.
According to Professor Melgosa Latorre, such research works prove that it is necessary to improve the traditional syste and design a new one to measure virgin olive oil colour: «We have already laid the foundations. We have a wide sample base and we know how to do a new colour card to characterize virgin olive oils and control suitably the lighting and thickness of the samples». «We want colour to appear in bottles as another quality indicator and not only acidity as now», the scientist stresses; he also demands a higher support to instituciones and companies to finance this kind of research.
Together to Manuel Melgosa, of the Department of Optics of the Faculty of Science of Granada, the work group specialized in the study of virgin olive oil colour is made up of other specialists of the University of Granada (María del Mar Pérez Gómez and Enrique Hita), of the Fat Institute (CSIC) of Seville (María José Moyano y José Alba) and the Nutrition and Bromatology area of the Faculty of Pharmacy of Seville (Francisco Heredia).
Reference: Professor Manuel Melgosa Latorre. Department of Optics of the Faculty of Science. Phone numbers. 958-24 63 64 / 958-249493 / Mobile 659-719527
E-mail: mmelgosa@ugr.es
