Effect of the combined application of heat treatment and proteases on protein stability and volatile composition of Greek white wines

Aim: This work evaluates the effects of the combined use of heat treatment (HT, 75 °C, 2 min) and proteases (P) on the protein stability and volatile composition of two white wines, obtained from the Greek cv. Assyrtiko and Moschofilero. Methods and results: Wine protein stabilization was assessed by heat test, using RP-HPLC determination of pathogenesis-related proteins (PRP) and by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDSPAGE). The impact of bentonite and P + HT treatment on wine aroma profile was evaluated by GC-MS with liquid-liquid extraction. According to the heat test, in Assyrtiko wine the level of stability achieved with P + HT was comparable with that obtained by bentonite fining and for Moschofilero wine - where protein instability was higher - bentonite was more efficient. RP-HPLC profiles showed that, in general, higher percentages of chitinases (CH) than thaumatin-like proteins (TLP) were removed by both bentonite and P + HT, with a similar efficiency for the two treatments and sometimes better performances for the latter. Conversely, TLP were removed more efficiently by bentonite, even if some fractions were eliminated to a slightly higher extent by proteases. In the conditions of the experiment, bentonite resulted in minor changes to the wine aroma profile. However, heating during protease treatment modified wine volatile composition, reducing the concentration of esters produced during fermentation while simultaneously increasing the contents of certain esters characteristic of aging such as ethyl lactate. Conclusions: The combination of proteases and heat treatment may be a promising technique for protein stabilization of wines. However, further investigations are needed to optimize the time:temperature ratio of the heat treatment in order to obtain the maximum protease activity and the minimum thermal deterioration of the wine quality. Significance and impact of the study: The results of this study have a practical interest for both the scientific community and wine sector, contributing to knowledge of the efficacy and limitations of the use of protease enzymes for wine stabilization.