Phenolic, flavonoid, and amino acid compositions reveal that selected tropical seaweeds have the potential to be functional food ingredients

Seaweeds are a rich source of metabolites, including polyphenols, flavonoid, and amino acids, and have been used as food or food supplements in Asian countries since ancient times. Different metabolites are being reported from seaweeds worldwide, but there has been little reported, so far, on tropical seaweeds of the Arabian Sea coast. Eighteen abundant tropical seaweeds (7 green, 4 brown, and 7 red) were collected from the Saurashtra Coast of the Arabian Sea (Gujarat, India), and their phenolic, flavonoid, and amino acid compositions were studied. Liquid chromatography/mass spectroscopy revealed the presence of important polyphenols and flavonoids. High-performance liquid chromatography detected ascorbic acid and 19 natural flavonoids, including gallic acid, catechins, myricetin, proanthocyanin, kaempferol, quercetin, apigenin, and lutein. The highest amount of ascorbic acid (26.3 mg/g DW) was detected in Ulva fasciata, followed by Ulva lactuca (20 mg/g DW) and Grateloupia indica (11.5 mg/g DW). All green and red seaweeds contained gallic acid, with the highest amount (9 mg/g DW) in Amphiroa anceps, followed by Caulerpa racemosa var. macrophysa (8.5 mg/g DW) and Caulerpa corynephora (4 mg/g DW). The highest catechin content was found in A. anceps (14 mg/g DW), followed by C. racemosa var. macrophysa and Spatoglossum asperum (11 mg/g DW). Amino acids are primary metabolites that are important in the human diet. Among the green seaweeds, the highest amounts of leucine (0.2 mg/g protein), lysine (0.5 mg/g protein), methionine (0.4 mg/g protein), phenylalanine (0.2 mg/g protein), valine (1.3 mg/g protein), proline (48 mg/g protein), and tyrosine (28 mg/g protein) were detected in Caulerpa spp. The highest amounts of the sulfur-rich amino acids, methionine (1 mg/g protein), and cysteine (9 mg/g protein), were found in the red seaweed Gracilaria corticata. This study reveals that tropical seaweeds, including Caulerpa spp., Spatoglossum asperum, Stoechospermum polypodioides, Gracilaria corticata, and Grateloupia indica, are promising as functional food ingredients or dietary supplements for daily intake. Practical applications The present study demonstrates that tropical seaweeds, especially Caulerpa species (corynephora, racemosa and chemnitzia), S. asperum, S. polypodioides, G. corticata, and G. indica are rich source of phenolic and flavonoid compounds, including ascorbic acid, gallic acid, catechins, myricetin, proanthocyanin, and essential amino acids. These metabolites are natural antioxidants and own high bioactivity. The article reveals the functional food or nutraceutical potential of tropical seaweeds. As practical perspective, tropical seaweeds such as Caulerpa has potential to be processed further as a functional food or may be explored for the extraction of nutraceuticals.