Immune activities of the water-soluble yam (Dioscorea oppositeThunb) polysaccharides as affected by thermal, acidic and enzymatic treatments

Yam (Dioscorea opposite Thunb) polysaccharides have in vitro immune activities. The present study investigated the effects of thermal, acidic, and enzymatic treatments on immune activities of the water-soluble yam polysaccharides, via assaying their abilities to activate three immune-related cells (splenocytes, macrophages, and natural killer cells) and to mediate the secretion of eight immune molecules (IL-2, IFN-γ, IL-4, IL-1β, IL-6, TNF-α, iNOS, and LZM). The results indicated that the yam polysaccharides heated at 100°C for 30–60 min, or digested by simulated stomach acid for 1–2 h, or digested by two proteases and two amylases for 1–3 h showed unchanged immune activities (P > 0.05). However, hydrolysis of the yam polysaccharides by HCl solution of 3 mol/L for 3–6 h brought about lower activities significantly (P < 0.05). It is evidenced that the yam polysaccharides can keep their immune activities during thermal processing and body digestion, but stronger acid is potential to destroy their immune activities.