Protein instability in wine: a review
Protein instability can lead to the appearance of haze and deposits in wines, an aesthetic problem caused by the presence of grape proteins, mainly thaumatin-like proteins (TLPs) and chitinases that, under certain conditions, can become insoluble and aggregate into light-dispersing particles to make wines appear turbid. Since hazy wines are not saleable, this instability is generally prevented via bentonite fining, a treatment effective in removing the grape proteins responsible for haze formation, but with several drawbacks including the loss of wine loss, disposal costs, and removal of volatile compounds thus lowering the overall wine quality. As a consequence alternatives to bentonite are highly desirable, but for them to be successful, an in-depth understanding of the causes of protein hazing is required as this has the potential to lead to the development of novel, efficient, and environmentally sustainable winemaking processes to prevent haze from forming. In this talk an overview on the current understanding of the mechanism of haze formation will be given. In addition, a discussion on how the recent advances in the area allowed the elaboration of innovative strategies for protein stabilization of wines will be presented.
Protease application in winemaking to achieve protein stability of the wine
R. Schneider, Oenobrands (France)
Proteases are enzymes are naturally occurring in living organisms and especially involved in the digestion mechanisms. They are also used for food or non-food applications. In the food industry, traditional processes take advantage of protease such as milk coagulation using calf rennet or malting. Proteases are now used as technical aids in many food processes depending on their specificities such as for instance, production nutritional supplements, reduction of food allergenicity, meat tenderization, chill haze prevention in beer, or for dairy production and maturation.
In the wine industry, the use of acid proteases such as aspergillopepsin I and bacillopepsin has been investigated to prevent protein instability. Its authorization in enology is under discussion by OIV, and for the moment, only aspergillopepsin I was considered as potentially usable for health reasons. The main issue for the application of acid protease for protein stabilization is that amongst the two main unstable proteins involved in the haze formation in wine, the thaumatin-like proteins (TLPs) are not directly clevable by the zymes : a preliminary unfolding process is need to let them hydrolyzed, that can be reached by a heat treatment.
Oenobrands has developed, in the Rapidase, range an enzymatic preparation of Aspergillopepsin I from Aspergillus niger for wine protein stabilization: Rapidase Proteostab. The global solution proposed by Oenobrands includes, after Rapidase Proteostab addition in must, a heat treatment at 72°C for 2 minutes. Lab and industrial trials demonstrated the efficiency of this process and no detrimental side-effects of the heat treatment were observed if performed correctly.