Rapid optical method for tannins estimation in red wines

Abstract

In this work, an innovative analytical method has been proposed for fast and reliable in-line analysis of tannins in wines; the method is fast, does not require sample preparation and is based on the selective reactivity of tannins in a mixture containing proteinaceous matter (i.e. gelatin), under pH 3.5, resulting in the formation of white cloudiness. The modification of the optical properties of the wine/gelatin mixture is selectively associated to the tannins content, and it is detected with high accuracy by an optical prototype instrument, namely a Spectral-Sensitive Pulsed Photometer (SSPP) which has been previously described in the literature. The SSPP operate with a wavelength-sensitive pulsed electromagnetic source, with maximum emission around 890 nm, eliminating potential interferences from wine color. Preliminary results showed potentialities in the quantification of procyanidins in red wines, obtaining non-linear correlations with values obtained using the Adams-Harbertson colorimetric assay (R2 up to 0.966). Main advantages involve the high selectivity of the reaction responsible for turbidity formation, and simple, cost-effective and dimensionable technology of the optical device; these properties have suggested the potential exploitation of the method to support decisional strategies along the supply chain, improving the control of the production process and the quality of wines. 

The analytical method has been proposed for obtaining patent protection at the National (Patent nr. 102019000002585, 22 February 2019) and International (PCT/IB2020/051304, 12 March 2020) levels.