A wine arabinogalactan-protein that reduces heat-induced wine protein haze

An arabinogalactan-protein which reduced the heat-induced turbidity of protein in wine was purified from a red wine. The arabinogalactan-protein (AGP) was composed of a central 3-linked galactan core carrying, at position 6, 6-linked galactan chains which were in turn heavily substituted at positions 3 and 4 by terminal arabinofuranose residues and short 5-linked arabinan chains. The protein (13% by weight) was dominated by serine, alanine, hydroxyproline, and threonine and also contained a relatively high amount of the basic amino acids lysine and arginine. The molecular weight, estimated by universal calibration, was 210,000. Enzymatic removal of the terminal arabinofuranosyl units of the active AGP and subsequent partial shortening of the outer 6-linked galactan chains did not affect the haze protective activity. Periodate oxidation and then Smith degradation greatly reduced the size of the polysaccharide, its amount of protein, and eliminated its absorption at 280 nm and its haze protective activity.