Effects of Drying Methods on Content and Properties of Polysaccharides in Laminaria japonica

  Objective  Effects of various dehydration methods on the content and physiochemical properties of polysaccharides in the dried Laminaria japonica were studied.

  Method  Fresh L. japonica was dried by applying 2 W·g⁻¹ microwave-and-vacuum (MV1), 4 W·g⁻¹ microwave-and-vacuum (MV2), vacuum (VD), hot air (HA) or solar exposure (SE). Yield, SO₄²⁻, viscosity, scavenging activities on hydroxyl and superoxide anion free radicals of the polysaccharides in the dried kelp were determined.

  Result  Among the tried drying methods, SE produced kelp significantly lower on the yield (i.e., 7.87%), SO₄²⁻ content, viscosity, as well as the in vitro antioxidant activity of polysaccharides in L. japonica than HA or VD (P＜0.05). On the other hand, MV2 rendered dried kelp with the highest polysaccharides content at 13.83%, while MV1 with the greatest antioxidant activity (P＜0.05).

  Conclusion  Different drying L. japonica methods resulted in varied properties of the polysaccharides and kelp. By combining microwave and vacuum, the dehydration process maximally retained the functional components and antioxidant activity of the fresh kelp.