Influence of protein stabilization with aspergillopepsin I on wine aroma composition

The protein haze formation in white and rosé wines during storage, shipping and commercialization has always been an important issue for winemakers. Among the various solutions industrially proposed, the use of bentonite is certainly the most widespread. However, the harmful effects of this treatment are known either in terms of wine volume loss and wine flavour and aroma. The use of aspergillopepsin I -an acid endoprotease from Aspergillus spp- in must and wine has been recently approved by OIV and the European Commission for protein stability, coupled to a heat treatment. Beyond the established efficacy of this approach on wine stability, little is known about its influence on the wine aroma profile. The present study aims to evaluate the combined effect of heat treatment with proteases (HP) in musts on the concentration of 74 wine aroma compounds at lab and semi-industrial scale. Eight grape musts were treated with acid proteases and heated at 70°C for the lab-scale trials, and the concentrations of wine volatile compounds at the end of the alcoholic fermentation were compared with those deriving form a traditional white and rosé winemaking protocol. The must treatment induced a significant increase (one-way ANOVA, Tukey’s HSD p<0.05) of fatty acids (+17%) and acetate esters (+95%) in wines; conversely, monoterpenes diminished in HP samples (-40%). No differences were observed in the total ethyl esters concentration between treatments. Interestingly, HP musts increased the concentration of thiol precursors in grape musts and the free thiols in wines. Subsequently, a scale-up experiment was conducted at semi-industrial conditions on three different grape juices, according to the OIV prescriptions. Results are consistent with those of the lab-scale trials. The concentration of fermentation-derived fatty acids and acetates esters was higher in HP wines compared to controls (respectively, +28%, +53%), and no differences between treatments for ethyl esters. In contrast, the total terpenes decreased (-60%) in HP. Overall, no significant differences were found on the concentration of volatile compounds between HP and the sole heating treatment. Additionally, volatile thiols were quantified in wines obtained from Sauvignon Blanc grapes. Results were not statistically differentiated; however, HP enhanced the corresponding odour activity values (OAV) by, on average, 30%, mainly as a consequence of the increase in 4-methyl-4-sulfanylpentan-2-one. This study provided an initial evaluation of the impact of protein stabilization process with heat and proteolytic enzyme on the aroma profile of white and rosé wines.