Influence of oak species on the differentiation of aged brandies using chemometrics approach based on phenolic compounds UHPLC fingerprints

Abstract

Oak is the main material used in cooperage for making barrels and wood chips destined to aged spirits and wines. Quercus alba L., Quercus petraea L. and Quercus robur L. are three of the most commonly used oak species in cooperage companies. The geographical origin and botanical species influence the composition of the wood and the subsequent impact on the sensory profile of the product aged in the wooden barrels. Depending on the type of oak in which the wines and spirits are aged, the final products obtained are very different. Phenolic compounds are the main components extracted from the wood during ageing, and they depend on many factors. Botanical species, toasting level, barrel dimension and ageing time are parameters that affect the type and amount of polyphenols that the wood releases into the wines and distillates.
Combining instrumental fingerprints with Chemometrics, known as fingerprinting methodology, is a novel strategy that allows information about the composition of brandy samples to be obtained in a non-selective way, as it is not necessary to identify or quantify the compounds present in the sample. Through a chemometric study of the instrumental fingerprint, it is possible to identify known or unknown areas of the chromatograms characteristic of a particular type of sample. Ultra-High-Performance Liquid Chromatography (UHPLC) was used to acquire the instrumental fingerprints of the phenolic profile at 280 nm and 320 nm of aged brandy samples. The chromatographic fingerprints of more than 100 samples of brandies produced from different distillates and aged in 350-litre barrels from three different oaks, Quercus alba L., Quercus robur L., and Quercus petraea L.; with two different degrees of toasting, medium and light; and during 14 and 28 months were recorded and pre-processed for the chemometric approach centred on patterns recognition.
Unsupervised patterns recognition techniques such as principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied. The results of these analyses revealed the influence of distillate type, ageing time and toasting level on the natural grouping of samples, being the first one the variable that most affects the natural grouping of samples. Nevertheless, for the same type of distillate, ageing time and toasting level, variables that influence the ageing process, groupings of the samples were observed depending on the type of wood in which they were aged. This methodology is very interesting, since it is not necessary to know or identify all the compounds that appear in the chromatographic profile to determine in this case, whether the brandy is aged in one or another type of oak. The application of the results obtained could lead in the future to a model for the discrimination/classification of brandies, based on the type of oak in which it is aged.