Analysis of pyranoanthocyanins, polymeric pigments and colour parameters in Port wines

Context & aim: The two major categories of Port wines, Tawny and Ruby, are defined by their ageing conditions, with associated oxidative conditions being much more pronounced in the case of the former than the latter. The main aim of this study was to determine if, independently of the producer, all Port wines can be grouped into these styles based on their chromatic and pigment characteristics.

Methods: A total of 32 Port wine samples comprising eight different styles were provided by five different producers of the Douro region in Portugal for this work. All the samples were filtered prior to analysis for anthocyanin determination using an HPLC-DAD-ESI/MS, and unfiltered samples were used for the determination of colour parameters and CIE Lab coordinates. The samples were measured in triplicate for statistical analysis.

Results: The chromatic analysis of the Port wines showed Ruby style Ports to have a higher colour intensity and lower hue (°) than Tawny style Ports. The PCA analysis of colour parameters and CIE Lab coordinates clearly shows two separate clusters representing Ruby styles and Tawny styles respectively. Overall, Tawny style Ports had traces of or non-detected anthocyanins monoglucosides, a few styles having < 10 mg/L in the form of malvidin-3-Oglucoside equivalent; meanwhile Ruby styles showed higher concentrations of anthocyanins as detected by HPLC, sometimes reaching values close to 100 mg/L. The major anthocyanin family found across all wines (even in trace amounts) were pyranoanthocyanins, specifically vitisin A and coumaroylated vitisin A.

Main conclusions: The results prove that in terms of all the parameters studied there is a clear division between the two major styles of Port wines, which can be attributed to the differences between the ageing process of these two types of wines.