Towards multi-purpose valorisation of polyphenols from grape pomace: Pressurized liquid extraction coupled to purification by membrane processes

INTRODUCTION: Oenological tannins are widely used in winemaking to improve some characteristics of wines [1] being the antioxidant properties probably one of the main reasons [2]. However, commercial tannins have different botanical sources and chemical composition [3] which probably determines different antioxidant potential. There are some few references about the antioxidant properties of commercial tannins [4] but none of them have really measured the direct oxygen consumption by them. The aim of this work was to measure the kinetics of oxygen consumption by different commercial tannins in order to determine their real capacities to protect wine against oxygen. MATERIAL AND METHODS: 4 different commercial tannins were used: T1: condensed tannin from grape seeds, T2: gallotannin from chinese gallnuts, T3: ellagitannin from oak and T4: tannin from quebracho containing condensed tannins and ellagitannins.

The assessment of red wine mouthfeel relies primarily on the sensory description of its tannic properties. This evaluation could be improved by gaining a better understanding of the physicochemical properties of these tannins. Hence, the objectives of the present study were threefold: (1) to gain an insight into the sensory properties of subpopulations of proanthocyanidic tannins of different molecular sizes obtained through several ultrafiltration steps, (2) to quantify the kinetics of haze formation of these proanthocyanidic tannins in a dynamic polyvinylpyrrolidone (PVP) precipitation test, (3) to determine whether a correlation exists between the sensory and the precipitation data.

Limited information is available on grape wall-derived polymeric structure/composition and how this changes during fermentation. Commercial winemaking operations use enzymes that target the polysaccharide-rich polymers of the cell walls of grape tissues to clarify musts and extract pigments during the fermentations. In this study we have assessed changes in polysaccharide composition/ turnover throughout the winemaking process by applying recently developed cell wall profiling approaches to both wine and pomace polysaccharides. The methods included gas chromatography for monosaccharide composition (GC-MS), infra-red (IR) spectroscopy and comprehensive microarray polymer profiling
(CoMPP) using cell wall probes.

Grapevine berries produce thousands of secondary metabolites of diverse chemical nature that have been largely detailed in the past due to their importance for defining wine quality. The wide Vitis vinifera diversity, resulting in thousands of different varieties well detailed in many studies regarding berries, is still not investigated in vegetative organs, leaves in particular. Deepening knowledge related to this aspect could be of great interest for many reasons (for example the possibility of using leaf extract for pharmaceutical, cosmetic and nutrition purposes) but, above all, for understanding the susceptibility of different grapevine varieties to pathogens.

Laboratório de Análisis del Aroma y Enologia (LAAE). Department of Analytical Chemistry, Faculty of Sciences, Universidad de Zaragoza, 50009, Zaragoza, Spain, During alcoholic fermentation, fusel (or Strecker) aldehydes are intermediates in the amino acid catabolism to form fusel alcohols following the Ehrlich Pathway (1). One of the main enzymes involved in this pathway is Alcohol Dehydrogenase (ADH), whose activity is highly strain dependent and determines the rate of conversion of aldehydes into fusel alcohols (2). This enzyme has a Zn2+ catalytic binding site, which suggests that the must Zn2+ levels will most likely influence the rate of reduction of aldehydes into alcohols. On the other hand, SO2 is commonly used in winemaking for its antiseptic and antioxidant properties.