Electric Method for the Desulfation of Polysaccharides From Red Microalgae (Porphyridium cruentum) Cultures

Sulfated polysaccharides from the red microalgae Porphyridium cruentum demonstrate unique physicochemical properties and antiviral activity. Despite growing interest, it is yet unclear how the sulfates within these polysaccharides affect their rheological properties and whether they are required for the antiviral activity. We report a nondestructive method to deplete sulfates from these polysaccharides by directly exposing the growth medium to a moderate electric field (3.43 V/cm); a 5 min exposure yielded a polysaccharide fraction around the cathode, which we collected and compared to polysaccharides extracted via a traditional, ethanol-based method. Although the electric field did not affect the sugar composition of the polysaccharide and retained its gel-like properties, it substantially reduced its sulfate content (from 5.8% to 1.2%), viscosity (by fivefold), and stiffness (by eightfold) relative to the ethanol-separated fraction. Yet, the bioactivity of the sulfate-depleted polysaccharide against Herpes simplex virus 1 was only slightly reduced (~15%), suggesting that the sulfate groups do not significantly contribute to the antiviral potency of this polysaccharide. The reported electric-field separation methods is, therefore, a simple, straightforward, and nontoxic means for the direct recovery of desulfated polysaccharides from P. cruentum cultures, yielding a low-toxicity and highly stable gel-like material with enhanced amenability for antiviral applications.