Evaluation of the chemical, functional, antioxidant, and antidiabetic properties of Kappaphycus alvarezii (Red seaweed)

Abstract:

Kappaphycus alvarezii is one of the edible red seaweeds commercially cultivated in Sri Lanka and available in large quantities; however, people are unaware of their biochemical and bioactive importance. This study aimed to investigate the chemical and functional properties of K. alvarezii powder and the bioactivity of different solvent extracts of K. alvarezii. Compositional analysis on a dry-weight basis showed that it was rich in fiber (9.82%), ash (28.87%), and carbohydrates (58.41%), mainly carrageenan (37.70%), but low in fat (0.68%). It contained water-soluble red pigment phycobiliprotein (1.13 mg/g) and other health-promoting pigments such as chlorophylls and carotenoids. It showed good solubility (0.26 g/g), Swelling capacity (11.07 mL/g), water-holding capacity (8.87 g/g), and oil-holding capacity (3.04 g/g), with a significant correlation with increasing temperature. Extraction yield was significantly higher in the methanolic extract (22.16%). Water extract had significantly higher level of total phenolic (1.85 mg gallic acid equivalent/g extract) and flavonoid content (0.88 mg rutin equivalent/g extract), exhibited significantly higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity (IC₅₀: 6.36 mg/mL), total antioxidant (6.52 mg ascorbic acid equivalent (AAE)/g extract, reducing capacity (2.86 mg AAE/g extract), and H₂O₂ scavenging activity (IC₅₀: 1.62 mg/mL), compared to ethanol and methanol extracts, whereas alpha - amylase inhibition activity was significantly high in ethanolic extract (IC₅₀: 12.13 mg/mL). This study suggested that K. alvarezii might be potentially used as a functional food or ingredient in the food and pharmaceutical industries to improve human health.