Abstract
To test the effect of the moment of bentonite addition, co-addition of tannins, and bentonite type on the differential affinity of pathogenesis-related (PR) proteins towards bentonite during grape must fermentation, three separate experiments were set up. PR proteins in the obtained wines were analyzed by reverse phase and size exclusion high-performance liquid chromatography (HPLC). The most significant reduction of bentonite dose and PR protein concentration was achieved by applying bentonite in the last third of fermentation. Particular thaumatin-like proteins (TLP) and proteins with lower molecular mass in general were more affected than others, while TLPs were more affected than chitinases. Exogenous enological tannins interacted with particular PR proteins, mostly TLPs, and lowered the total bentonite dose required. The combined application of tannins and bentonite in fermentation removed more PR proteins than bentonite alone, but did not achieve a synergistic effect in reducing the bentonite dose. Various bentonite types, including two Na-activated bentonites, an activated Na bentonite with specifically adsorbed silica, and an active Na-Ca bentonite, exhibited differential affinity towards different PR proteins. The results obtained could be used in developing wine fining protocols which combine treatments with complementary affinity for adsorption and removal of PR proteins, and in this way achieve greater efficiency of bentonite fining by reducing its total dose, which is of significant interest to the wine industry.
Highlights
Developed protein haze or sediment in bottled white wine is considered a serious quality defect: such wines are perceived by consumers as faulty and are not marketable [1]
All the treatments involving bentonite addition during fermentation significantly reduced the total amount treatments involving bentonite addition during fermentation significantly reduced the total amount required in relation to standard fining after fermentation in CO treatment according to heating with required in relation to standard fining after fermentation in CO treatment according to heating with tannins stability test
Four TL proteins and two chitinases were tentatively identified identified by RP-high-performance liquid chromatography (HPLC), while seven fragments of different molecular weight, among which five by reversed-phase high-performance liquid chromatography (RP-HPLC), while seven fragments of different molecular weight, among which five with weights with weights commonly considered to correspond to PR protein species, commonly considered to correspond to PR protein species, were tentatively were tentatively identified by Size Exclusion High-Performance Liquid Chromatography (SE-HPLC)
Summary
Developed protein haze or sediment in bottled white wine is considered a serious quality defect: such wines are perceived by consumers as faulty and are not marketable [1]. Protein haze in wine originates mainly from denaturation and aggregation of relatively small quantities (from 10 to several hundreds of mg/L) of the so-called pathogenesis-related (PR) grape (Vitis vinifera L.) proteins [2]. The PR proteins typically have lower molecular mass (15–35 kDa) and lower isoelectric point (pI), and mainly pertain to the families of thaumatin-like proteins (TLPs, PR-5 family) and chitinases (PR-3 family) [3], a minor involvement of β-1,3-glucanase (PR-2) and ripening-related proteins in the formation of protein haze was established [4,5]. Chitinases were recognized as primary causative agents of wine protein haze due to lower melting temperature [6], shorter half-life, and irreversible aggregation [7] in relation to other wine PR proteins. Protein instability and potential haziness in a particular wine depend on the total concentration of proteins, and on their composition [4].
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