Stephan Sommer,* Julia Graves, Jan-Peter Hensen, Fiona Hoening, A. Faeth Anderson, and Fabian Weber
*California State University, Fresno, Viticulture and Enology, 2360 E. Barstow Ave. M/S VR89, Fresno, CA, 93740 (ssommer@csufresno.edu)

Polysaccharides can be extracted from grapes and microbial cells during wine pro­duction and play an important role in the physical stability of wine. Especially pectin and pectin fragments as well as mannoproteins have been shown to interact with polyphenols, proteins, crystals and other wine components and influence their solu­bility and colloidal stability. Our experiments also revealed that polysaccharides have the ability to disrupt the interaction between proteins and polymeric pigments, lead­ing to data artifacts in pigment precipitation assays. The Harbertson-Adams Assay for example relies on bovine serum albumin to precipitate tannins and precipitable polymeric pigments. In the presence of certain polysaccharides, this complexation is impaired and the reading for non-precipitable polymeric pigments (np-PPs) is artifi­cially increased. Other trials have revealed that pectin fragments have the ability to bind anthocyanins and pigments, which leads to an apparent decrease in monomeric anthocyanins and an increase in polymeric pigments. These pigment-polysaccharide adducts (PPA) have been identified in model systems and, more recently, in red wines where they are responsible for a portion of the total color. These adducts are not bleached by sulfite but rapidly disrupted by pectolytic enzymes. They also further in­crease the reading for np-PPs, making the analysis of polymeric pigments in the pres­ence of polysaccharides less reliable for multiple reasons. While the analytical portion can be addressed by our modified assay conditions, the percentage and chemical composition of PPAs in the course of wine production and aging remains mostly un­known. There appear to be several reaction and binding mechanisms that give these adducts a varying degree of stability with very different implications for young wines compared to their aged counterparts. This ongoing research has important implica­tions not only for the characterization of red wine pigments but also for the targeted use of polysaccharides for color improvement and long term stability.

Funding Support: n/a