Dietary fibre and physicochemical properties of edible Spanish seaweeds

Total dietary fibre content of five edible marine Spanish seaweeds: Fucus vesiculosus, Laminaria digitata (Kombu), Undaria pinnatifida (Wakame), Chondrus crispus (Irish moss), and Porphyra tenera (Nori) ranged from 33.6 to 50% of which 19.6 to 64.9% was soluble. For brown algae, the soluble fibre obtained by the AOAC method followed by dialysis, contained uronic acids from alginates and neutral sugars from sulphated fucoidan and laminarin. For red seaweeds, the main neutral sugars corresponded to sulphated galactans: carrageenan (Chondrus) or agar (Nori), respectively. Insoluble fibres (12-40%) were essentially made of cellulose, plus residual fucose-containing polysaccharides, except for the red seaweed Nori, which contained an insoluble mannan acid xylan. Protein content in powdered algae was higher in red (20.9-29.8%) than in brown seaweeds (6.9-16%), although protein digestibility was apparently low as inferred from preliminary in vitro results with Fucus and Laminaria. Ashes (21-39.8%) and sulphate content (2.8-10.5%) were high in all seaweeds. Minor components were lipids (0.2-2.5%) and extractable polyphenols (0.4%). Regarding the physicochemical properties, oil retention was low, while swelling, water retention, and cation exchange capacity were higher in brown algae, related to their higher uronic acid plus sulphate content.