Measuring Colour of Virgin Olive Oils

Abstract: From the economical and social importance of virgin olive oils in Spain and Italy, nowadays an improved color characterization of these products is highly desirable. Following this goal, in this paper we propose a Modified Uniform Oil Color Scale (MUOCS) and a low-cost portable electronic device to measure color of virgin olive oils using this new scale. The MUOCS has been developed from a sample of 1700 virgin olive oils produced in Spain (M. Moyano, Ph.D. Dissertation, Universidad de Sevilla, Spain, 2002) using the geometry proposed by the Optical Society of America - Uniform Color Scales (OSA-UCS), and the DIN99d color space (G. Cui et al., Color Research & Application 27, 282-290, 2002). From the same number of 60 standards than previously proposed color scales for virgin olive oils, such as the BTB scale (R. Gutiérrez et al., Grasas y Aceites 37,2, 1986) and the UOCS (M. Melgosa et al., Journal of the American Oil Chemists' Society 81, 323-330, 2004), the MUOCS achieves promising improvements. For example, the average color-difference from nearest MUOCS standards to the previously mentioned 1700 virgin olive oils was 2.9 CIELAB units, while 8.2 and 4.0 CIELAB units were obtained from the BTB and UOCS standards, respectively. We have designed an electronic portable device providing the nearest BTB and MUOCS standard for a given virgin olive oil sample. This device has a Nichia NSPW300BS white LED and a Hamatsu CCD S9706 color sensor, using a Microchip PIC18f2550 as microcontroller. The apparatus performs transmittance measurements using 5 mm thickness samples, and has been calibrated on the basis of conventional measurements of the 60 BTB standards with a JASCO V650 spectrophotometer. Recalibration is allowed by the system. The whole cost of materials employed for this device is estimated below 70 Euros.