Abstract:
The demand for seaweed is increased recently due to its high nutritional and
medicinal values. Therefore, this study evaluated the nutritional composition
and antioxidant properties of methanolic extracts of selected green
(Enteromorpha spp.), brown (Turbinaria spp.), and red (Laurencia spp.)
seaweeds collected from the coastal area of Delft Island in the Northern region of
Sri Lanka. Collected samples were dried under shade until they reached a
constant moisture content. These dried samples were powdered and analyzed
for proximate composition (crude protein, crude fat, crude fiber, ash, moisture,
and carbohydrate contents) by AOAC methods. Among the three selected species,
Laurencia spp contained the highest (p<0.05) amount of crude protein
(42±2.31%), and ash content (38.99±1.02%), whereas Enteromorpha spp had
the highest (p<0.05) carbohydrate content (47.92±2.07%) and Turbinaria spp
contained the highest (p<0.0.5) amount of fat content (2.34±0.02%). The crude
fiber content of the selected seaweeds ranged from 8.96±0.15 to 9.73±1.10%.
The selected dried samples were extracted by 70 % v/v methanol for different
durations (2, 4, and 6 hours) at 200 rpm using a mechanical shaker for the
antioxidant analysis. Extracts were analyzed for antioxidant properties such as
total phenolic content (TPC) [expressed as Gallic Acid Equivalent/ g dry matter
(GAE/g DM)], total antioxidant capacity (TAC) [expressed as Ascorbic Acid
Equivalent/ g DM (AAE/g DM)], and 2,2-diphenyl-1-picrylhydrazyl (DPPH)
radical scavenging activity (expressed as IC50 value which is inversely related to
antioxidant activity). The highest TPC and antioxidant activity were obtained in
the extract obtained after 6 hours of extraction compared to 2 and 4 hours.
Among the species analyzed, Turbinaria spp exhibited the highest (p<0.05)
content of TPC (8.10 ± 0.72 mg GAE/g DM), TAC (4.49 ± 0.43mg AAE/g DM) and
antioxidant activity (IC50 value- 0.08 ± 0.05 mg/ mL). Gas chromatography
analysis identified the different types of fatty acids present in three seaweed
species (C8:0, C10:0, C11:0, C11:1, C12:0, C16:0, C16:1, C17:1 and C18:1). This
study concluded that the tested seaweeds showed the beneficial health
properties and could be effectively used to prepare value-added food products.
