Structural Characterization and Immunostimulatory Activity of Heteropolysaccharides from Fuzhuan Brick Tea

Fuzhuan brick tea (FBT), one of the unique dark teas, has various health-promoting functions. In the present study, one polysaccharide fraction, namely FBTPS-2-1, was extracted and purified from FBT, and its structure and potential immunostimulatory activity were investigated. The results showed that FBTPS-2-1,one of typical heteropolysaccharides, was mainly composed of Gal, Ara, and Glc with little molar content of Man, Rha, GalA, and GlcA in molar ratio of 46.59:22.13:13.57:8.20:6.02:2.12:1.38 and molecular weight of 748 kDa. The backbone of FBTPS-2-1 contained -> 4)-beta-D-Galp-(1 -> 4)-beta-D-Galp-(1 ->, -> 4)-beta-D-Galp-(1 -> 4)-alpha-D-Glcp-(1 ->, -> 4)-alpha-D-Glcp-(1 -> 4)-alpha-D-Glcp- (1 ->, -> 4)-alpha-D-Glcp-(1 -> 4)-beta-D-Galp-(1 ->, -> 3)-beta-D-Galp-(1 -> 4)-beta-D-Galp-(1 ->, -> 3,6)-beta-D-Galp- (1 -> 3)-beta-D-Galp- (1 -> and -> 3,6)-beta-D-Galp-(1 -> 3,6)-beta-D-Galp-(1 ->. The linkages of branches in FBTPS-2-1 were mainly composed of alpha-L-Araf-(1 -> 3,6)-beta-D-Galp-(1 ->, -> 5)-alpha-L-Araf-(1 -> 3,6)-beta-D-Galp-(1 ->, -> 6)-beta-D-Galp41 -> 3,6)-beta-D-Galp-(1 ->, alpha-L-Araf-(1 -> 3,S)-alpha-L-Araf-(1 ->, -> 3,5)-alpha-L-Araf- (1 -> 5)-alpha-L-Araf-(1 ->, alpha-D-Galp-(1->3,5)-alpha-L-Araf-(1 -> and -> 5)-alpha-L-Araf-(1 -> 6)-beta-D-Galp-(1 ->. Furthermore, FBTPS-2-1 could increase the phagocytosis of macrophages and promote the secretion of NO and a variety of inflammatory cytokines, including TNF-alpha, IL-1 beta, and IL-6, indicating noticeable immune enhancement activity. Thus, FBTPS-2-1 could serve as a potentially functional food to improve human health by modulating the host immunoreaction.