Abstract Agar, a phycocolloid naturally extracted from Gracilariopsis heteroclada is strongly influenced by salinity. Wild stocks of G. heteroclada were exposed to varying salinities (20, 30, 40, 50, 60) for 6 days, and subsequently processed for agar extraction using 5 % NaOH. The extracted agar was evaluated regarding yield, gel rheology, colour composition, chemical properties, and infrared spectra. Results highlighted that hypersaline conditions (salinity 50) could produce high agar yield (4.77 %) and viscosity (10.67 mPa s), while agar samples at salinity 40 exhibited gels with high cohesiveness (6.35 mm), gel breaking strength (3.01 N), and gel strength (390.61 g cm−2) while having a rather high 3,6-anhydrogalactose content (7.49 %). All samples exhibited FTIR signature peaks at 930 cm−1, confirming the identity of extracted agar from G. heteroclada. Exposure at increasing hypersalinity increased the sulphate levels of agar from G. heteroclada, which implies synthesis of sulphated polysaccharides. Moreover, high 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities were obtained in acid hydrolysed agars at salinities of 40 (74.09 %) and 50 (75.57 %), suggesting that G. heteroclada agars from hypersaline conditions potentially offer antioxidative roles beyond its traditional food use.
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