Abstract
Wine protein instability depends on several factors, but wine grape proteins are the main haze factors, being mainly caused by pathogenesis-related proteins (thaumatin-like proteins and chitinases) with a molecular weight between 10~40 kDa and an isoelectric point below six. Wine protein stability tests are needed for the routine control of this wine instability, and to select the best technological approach to remove the unstable proteins. The heat test is the most used, with good correlation with the natural proteins’ precipitations and because high temperatures are the main protein instability factor after wine bottling. Many products and technological solutions have been studied in recent years; however, sodium bentonite is still the most efficient and used treatment to remove unstable proteins from white wines. This overview resumes and discusses the different aspects involved in wine protein instability, from the wine protein instability mechanisms, the protein stability tests used, and technological alternatives available to stabilise wines with protein instability problems.
Highlights
Proteins exist in wine at low levels, related to the protein content and composition of the grapes, which are dependent on the grape variety and maturation conditions, as well as on the winemaking process [1]
Total protein assays are limited concerning the prediction of wine protein stability and do not take into account the role that other wine components play in protein instability [12]
The trichloroacetic acid (TCA) test is established on the ability of this acid to precipitate all proteins present in wine, yielding results close to those obtained by the determination of the wine total protein content [8]
Summary
Proteins exist in wine at low levels, related to the protein content and composition of the grapes, which are dependent on the grape variety and maturation conditions, as well as on the winemaking process [1]. Proteins can be responsible for a wine colloidal instability, forming amorphous sediment or flocculate, and produce a suspended and undesirable haze before or after bottling [1,2,3,4,5] that can cause serious economic losses to the wine producers This instability is more important in white wines, as white wine limpidity is an essential sensory quality parameter. The most important proteins that have been related to wine protein instability are pathogenesis-related proteins of Vitis vinifera that include the chitinases and thaumatin-like proteins [2,16] These proteins can be slowly denatured and aggregate throughout wine storage, forming a light-dispersing haze [17]; this phenomenon needs to be prevented by removing them from the wine, usually by fining, before wine bottling [13]. Alternative techniques to bentonite fining for this goal have been studied, such as ultrafiltration [6,23,24], addition of proteolytic enzymes [25,26], flash pasteurisation [27,28], other adsorbents (silica gel, hydroxyapatite and alumina) [29], zirconium oxide [30,31,32], natural zeolites [33,34], chitin and chitosan [35,36], carrageenan [5,37] and the use of some mannoproteins [19,38]
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