Bimonthly variation in the chemical composition and biological activity of the brown seaweed Eisenia arborea (Laminariales: Ochrophyta) from Bahía Magdalena, Baja California Sur, Mexico

The aim of this study was to describe the bimonthly variation in the proximate chemical composition, alginate, and fucoidan yield and ethanolic extract content, including the anticoagulant and antioxidant activity of the extracts and quality tests of alginates, from blades and stipes of Eisenia arborea collected in Bahía Magdalena, Baja California Sur, Mexico. Significant differences were found in the chemical composition between months and also between the alga structures. The major constituents in both blades (53.8%) and stipes (47.6%) were carbohydrates and ash (28.4 and 33.9%, respectively). The crude ethanolic extract yield and the antioxidant activity in blades were higher than in stipes throughout the period with a maximum in September (5.4% and EC₅₀ = 82.7 μg mL⁻¹). The highest yield of crude fucoidan was obtained in September (20%) for blades and March (8.7%) for stipes. The anticoagulant activity of fucoidan was higher in January for blades and May for stipes. The alginate yield showed significant difference (p > 0.05) between blades and stipes. The highest yield for blades was obtained in November (21.3%) and for stipes in January (24.5%). Our results suggest that the best period to harvest the alga is from September to March, considering the higher yields and better properties of the extracts.