Saul Assunção Bicca,* Céline Poncet-Legrand, Stéphanie Roi, Julie Mekoue Nguela, Thierry Doco, and Aude Vernhet
*Institut Agro Montpellier, 2 Place Pierre Viala 34060 Montpellier, 34060, France  (saul.assuncao@supagrao.fr)

Mannoproteins (MPs) are proteoglycans from the outmost layer of yeast cell walls that are released into wine during alcoholic fermentation and aging on lees. The use of commercial MP preparations as additives to prevent precipitation/insolubility of tartaric salts and protein haze in white wines is widespread and regulated. However, MPs possess other properties. MPs can impact the colloidal stability of polyphenols and modulate the astringent effect of condensed tannins. The latter interact with salivary proteins, forming insoluble aggregates that cause loss of lubrication in the mouth and promote a drying and puckering sensation. However, the interaction mechanisms involved in the MP capacity to impact astringency are not fully understood, nor are the structure-function relationships of these macromolecules with this property. This study evaluated the impact of high molecular weight MPs in tannin-protein interactions. To this end, tannin-BSA aggregation kinetics (with or without MPs) were assessed through dynamic light scattering measurements over time. MPs clearly delayed tannin-BSA aggregation kinetics by preventing formation of micron-sized particles within one hour, but did not prevent precipitation after 24 hrs. This suggests that MPs interfere in tannin-BSA aggregation through formation of a tertiary system of MP-tannin-BSA. To examine structure-function relationships, four different kinds of MPs with specific polysaccharide structures were used to examine the impact of the polysaccharide moiety: A reference strain (BY4742), the two mutants ΔMnn4 (with no mannosyl-phosphorylation) and ΔMnn2 (linear N-glycosylation backbone), and a commercial enological strain (LMD47). To prevent tannin-BSA particle growth, the density/compactness of the polysaccharide moiety of MPs was a key factor.

Funding Support: Lallemand Oenology