White grape must processed by UHPH as an alternative to SO₂ addition: Effect on the phenolic composition in three varieties

Abstract

The quantity and distribution of polyphenols in musts play a fundamental role in the white winemaking. This is because these substances are exposed to oxidation reactions, which are catalysed by the polyphenol oxidase (PPO), leading to a decrease in the quality of the wines produced. PPO is inactivated by SO₂, but currently, due to the restrictions of the legislation, other methodologies are being investigated. Ultra-High Pressure Homogenization (UHPH) is a non-thermal physic technology that exerts an ultrahigh pressure pumping (>200 MPa) of a fluid through a valve in a continuous system. Passing through the valve causes a series of mechanical forces (impact, shear, cavitation, friction) which produce an antimicrobial and anti-enzymatic effect, as well as nanofragmentation in biopolymers. Since both, phenolic composition and PPO activity, depend on the variety, the research of the response of musts from different varieties to this technique is essential. This work investigates, by using HPLC techniques, the response of polyphenol oxidase activity, flavonols, flavanols, phenolic acids and total phenols to the application of a) the UHPH technique (working flow rate: 60 L/h, at 300 ± 3 MPa, inlet T of 4ºC, in-valve T of 95 ± 2 ºC for less than 0.2 s and an outlet T of 14 ºC) and b) SO₂ (total dose 60 mg/L) of musts of Xarel·lo (Xar), Moscatel de Alexandria (M) and Garnacha blanca (Gb) from the 2022 vintage. The impact of the techniques applied depended on the variety considered and the effectiveness of UHPH could be established in the following pattern: Xar ≥ M > Gb. Moreover, phenolic acids were more sensitive to the action of SO₂ than the UHPH. In general, with the exception of M must, phenolic acids, flavanols and total phenols responded similarly to both treatments applied.

Acknowledgements: This work is founded by Operational Groups of the European Association for Innovation (AEI) in terms of agricultural productivity and sustainability (operation 16.01.01 of the Rural Development Program of Catalonia (PDR) 2014-2022). Generalitat de Catalunya.