Significance of metal ion supplementation in the fermentation medium on the structure and anti-tumor activity of Tuber polysaccharides produced by submerged culture of Tuber melanosporum

The significance of metal ion supplementation in the fermentation medium on the structure and anti-tumor activity of Tuber polysaccharides was systematically studied in the submerged fermentation of Tuber melanosporum. The lowest weight-average molecular weight (Mw) (i.e., 115.3 × 104 g/mol) of intracellular polysaccharides (IPS) was obtained when Mg2+ and K+ was added in the fermentation medium. The IPS with the lower Mw exhibited a higher inhibition ratio against S-180 tumor cells. The compact conformation of extracellular polysaccharides (EPS) was formed when only K+ was supplied in the fermentation medium. Interestingly, EPS with compact conformation exhibited a higher inhibition ratio (i.e., 59.2%) than EPS with branched polymer chain (i.e., 9.2%) against A549 tumor cells. The highest inhibition ratio for EPS with α-glycosidic linkages against the tumor cell line HepG2 reached 32.2% when Mg2+ or K+ was supplied in the fermentation medium. The addition of metal ion Mg2+, K+, and their combination to the fermentation medium is a vital factor affecting the structures of Tuber polysaccharides, which further determine their anti-tumor activities. The information obtained in this work will be useful for the efficient and directed production of polysaccharides with anti-tumor activities by the submerged fermentation of edible fungi mycelium.