Fucoxanthin extracted and purified from Vietnamese Sargassum oligocystum Montagne, 1845 exhibits various biological activities. In this study, the ability of fucoxanthin to inhibit acetylcholinesterase (AChE), the antioxidant activities, and the expression of antioxidant enzymes were investigated. Fucoxanthin isolated from Vietnamese S. oligocystum showed no cytotoxic effects; moreover, it exhibited AChE inhibitory activity (with an IC₅₀ value of 130.12 ± 6.65 μg mL⁻¹) and antioxidant activity (with an IC₅₀ value of 3.42 ± 0.15 mg mL⁻¹). At concentrations of 50 and 100 µg mL⁻¹, fucoxanthin provided protection against amyloid β-protein fragment 25–35-induced neurotoxicity in a C6 neuronal cell line, and the survival of C6 cells was higher than 81.01% and 80.98%, respectively, compared to the control group (59%). Moreover, antioxidant enzyme activity and quantitative PCR analysis suggested that the neuroprotective effect of fucoxanthin resulted from regulation of the gene expression of antioxidant enzymes (CAT and GPx) and ER pathways (caspase-3 and Bax), as well as the promotion of expression of genes involved in PI3K/Akt signaling (GSK-3β), autophagy (p62 and ATG5), and the biosynthesis of ACh (VAChT and ChAT). Therefore, fucoxanthin extracted from the seaweed S. oligocystum in Vietnam is a potential feedstock source for the production of health foods that exert neuroprotective effects.

This study investigates seasonal biomass variations in Betaphycus gelatinus, a red alga cultivated in the field in Ninh Thuan, Vietnam, along with the chemical composition, structural properties, and bioactivity of its carrageenan. Monthly measurements over a one-year period revealed peak growth (2.02% per day) and carrageenan yield (59.61%) in June, identifying it as the optimal harvest period. FTIR and NMR analyses of carrageenan extracted from field-cultivated B. gelatinus showed hybrid κ- and β-carrageenan forms and a unique pyruvylated β-carrageenan structure not previously reported for this species. Bioactivity assays indicated high antioxidant potential, with a total antioxidant capacity equivalent to 48.30 mg ascorbic acid/g carrageenan and an ABTS radical scavenging IC50 of 3.64 µg/mL. Additionally, antibacterial tests demonstrated strong inhibition of Listeria monocytogenes (12.00 mm inhibition zone). These findings suggest that field cultivation is a sustainable approach for carrageenan production, yielding bioactive compounds with promising applications in pharmaceuticals, cosmetics, and food preservation as a viable alternative to wild harvesting.