Chemical characterization of sulfated polysaccharides from Gracilaria gracilis and Ulva lactuca and their radical scavenging, metal chelating, and cholinesterase inhibitory activities

This study was designed to evaluate the antioxidant and cholinesterase inhibitory activities of sulfated polysaccharides from Gracilaria gracilis (PGCL) and Ulva lactuca (PULV). PGCL and PULV were extracted and characterized with Scanning electron microscope-energy dispersive x-ray (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and Gas chromatography-mass spectroscopy (GC-MS). The radical (2,2-azinobis-3-ethylbenzothiazoline-6-sulfonate [ABTS] 2,2-diphenyl-1- picrylhydrazyl [DPPH], and hydroxyl [OH]) scavenging and metal chelating activities as well as their inhibitory effects on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities were also determined. SEM-EDX analysis revealed the presence of elements such as carbon, magnesium, calcium, phosphorus, and sulfur. The FTIR analysis also confirmed the presence of sulfate group in the polysaccharide samples. Some sugars such as glucose, galactose, arabinose, xylose, rhamnose, and allose were also identified using GC-MS. PGCL and PULV scavenged ABTS, DPPH and OH radicals in a dose-dependent manner. Moreover, PULV exhibited higher scavenging activity compared to PGCL. PGCL and PULV also reduced the activity of AChE (IC 50 = 132.73 and 106.93 µg/mL) and BChE (IC 50 = 124.93 and 93.45 µg/mL) respectively. PGCL and PULV exhibited antioxidant activity and possess cholinesterase inhibitory activity, hence these polysaccharides could be explored as ingredients for the development of functional foods with neuroprotective potentials.