Analysis of the colour profile of port wines using different instrumental methods and visual approaches

Abstract

Colour is an important quality parameter in wines and is the result of a complex mixture of pigments (including anthocyanins and their derivatives, quinones, xanthyllium compounds, etc.). Red wine colour changes over time, as pigments react between themselves and with other wine macromolecules (particularly polyphenols). During wine tasting, colour is normally assessed on the outer rim of the wine in a tilted glass, since most wines are too opaque to be analysed in the middle of the glass. Therefore, depending on the depth of observation considered, the perception of wine colour can be different. The current official (OIV) method for measuring wine colour is based on UV/Vis spectrophotometric determination of the spectrum. In the current official (OIV) method, the transmittance spectrum of a particular sample is measured and used to calculate CIE-L*a*b* parameters (L*, a* and b*), which define a single (predominant) colour for a particular wine. Reflectance colorimetry is an alternative well-established method for measuring colour in foodstuffs, which can also be used in translucent samples (such as wines) as long as a reflective background is used. In this work, a reflectance colorimeter was used to measure CIE-L*a*b* colour parameters of Port wine samples of different categories at different depths, in Petri dishes. The obtained results were compared with the parameters obtained using the OIV method. In addition, the colour profile of Port wine samples was analysed using the colorimetric approach described above. An (untrained) panel was asked to assess the colour hue of the wine samples in Petri dishes, using an unstructured line scale, with the goal of establishing a correlation with the colorimetric readings at the same depths. The results suggest the colorimetric method can be used as an alternative to the OIV method for estimating the L* and H* parameters (the most important for wine colour definition), being quicker and more informative. In addition, there is a good correlation between H* parameter of colorimetric readings and the visual assessment of colour hue at all tested depths, being slightly better at lower depths. The colorimetric determination of wine colour at different depths can be conveniently used to characterize the visually perceived hue of Port wines.

Date of Award	30 Jan 2017
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Francisco Manuel Morais Sarmento de Campos (Supervisor) & Cristina L. M. Silva (Co-Supervisor)