Stability of 3-mercaptohexanol during white wine storage in relationship to must pre-fermentative fining

Abstract

3-Mercaptohexanol (3MH) is a volatile thiol occurring in several white and red wines, where it can contribute to fruity attributes. Its content is typically high in wines from certain grape varieties, in particular Sauvignon blanc, where it is considered a varietal marker. The strong nucleophilic character of thiols makes 3MH rather unstable during wine storage, due to the presence of several strong electrophilic species. Among these electrophilics, those arising from the oxidation of flavan3-ols such as catechin and epi-catechin have been indicated as critical for 3MH stability. Accordingly, there is a generalized interest towards the ability of vinification practices to reduce 3MH loss during aging through the management of wine flavan-3-ols content.
In the present study, Lugana white wines obtained using different products for pre-fermentative fining (PVPP, vegetable proteins, potato proteins, casein), as well without any fining, were adjusted to 30 mg/L of free SO2, spiked with a known amount of 3MH and submitted to aging at 24°C in ermetically sealed vials in the presence of 7 mg/L of dissolved oxygen.  Flavanol content of must and wines was assessed by means of HPLC, whereas 3MH was analyzed after aging by means of GC-MS after derivatization with ethyl propiolate.
The type of fining induced significant differences in the content of must and wine flavan-3-ols, with combinations of PVPP and vegetable proteins giving the largest flavan-3-ol decrease compared to control. Upon aging, wines fined with combinations of PVPP and vegetable proteins resulted in reduced 3MH loss, highlighting the positive influence of certain types of fining on wine aroma stability. Conversely, larger 3MH losses were observed when pre-fermentative fining was conducted using casein.  
The results of these study highlights the importance of fine tuning pre-fermentative fining to increase wine aroma stability and shelf-life