Use of computational modelling for selecting adsorbents for improved fining of wine

Abstract

The occurrence of faults and taints in wine, such as those caused by microbial spoilage or various taints, have resulted in significant financial losses to wine producers. The wine industry commits significant financial resources towards fining and taint removal processes each year. Fining involves the addition of one or more adsorptive substrates to juice or wine to bind certain components, thus reducing their concentration [1]. However, these processes are often not selective and can also remove desirable flavour and aroma compounds. Computational modelling techniques have not previously been exploited by the wine sector but have been used in other fields to predict the behaviour of target compounds with selected substrates. This study aimed to better elucidate the binding interactions between wine components (both desirable and undesirable) and common adsorbents through computational modelling and laboratory scale fining trials in order to improve the selection of adsorbents for specific fining or taint removal applications. The binding energies for a range of volatile compounds associated with common wine faults and taints, including guaiacol, 4-methylguaiacol, cresols and syringol (smoke taint), 4-ethylguaiacol and 4-ethylphenol (Brettanomyces spoilage), 3-isobutyl-2-methoxypyrazine (IBMP; ladybird taint), geosmin and methylisoborneol (fungal taint) and trichloroanisole (cork taint), as well as volatiles associated with varietal aroma and flavour, including esters, C13-norisoprenoids and monoterpenes, or oak maturation, including cis- and trans-oak lactone, vanillin and eugenol, were calculated against a range of adsorbent substrates, including bentonite, polyvinylpolypyrrolidone (PVPP) and α-cyclodextrin (α-CD) using the density functional theory as implemented in FHI-aims, a software package for atomic scale materials modelling. The computational data suggests that α-CD could be used to selectively remove a variety of different molecules but it is less suitable for removal of IBMP. In fact, the strongest interaction comes from materials with strong hydrogen bonding systems, such as eugenol and vanillin. PVPP is a purely hydrogen-bonding sponge. It actively excludes substrates which do not hydrogen bond very well; thus, it has a very high selectivity for vanillin, and other molecules with pendant hydroxyl functionalities in a non-sterically limited environment (such as certain phenols). This presentation will comprise results from computational modelling experiments and fining experiments conducted in the laboratory. Quantitative chemical analysis of wine volatiles before and after fining treatment enables predictions based on computational approaches to be evaluated.

1. Castellari, M., Versari, A., Fabiani, A., Parpinello, G.P. and Galassi, S. (2001) Removal of ochratoxin A in red wines by means of absorption treatments with commercial fining agents. Journal of Agricultural and Food Chemistry, 49, 3917–3921.