Carbon Dots from Seaweed Biomass: Characteristics, Bioactivities and Retardation of Lipid Oxidation in Pacific White Shrimp During Refrigerated Storage

Seaweeds are valuable marine resources rich in polysaccharides and polyphenols. Carbon dots (CDs) from Gracilaria salicornia (GS-CDs), Halymenia dilatata (HD-CDs), Sargasum polycystum (SP-CDs), Spatoglossum asperum (SA-CDs), Ulva lactuca (UL-CDs), and Caulerpa peltata (CP-CDs) were synthesized by a hydrothermal process and characterized by FTIR, XPS, and SEM-EDX. All the CDs had sizes less than 10 nm with spherical morphology and various functional groups. UL-CDs showed the strongest UV-A blocking efficacy via the measurement of light transmission (p < 0.05). HD-CDs exhibited the highest DPPH-RS-A (148.32 ± 1.51 μmol TE/L) and FRA-P (717.24 ± 7.87 μmol TE/L), whereas SA-CDs had the highest ABTS-RS-A (1043.40 ± 3.00 μmol TE/L). HD-CDs had antifungal activity against both Aspergillus flavus and Aspergillus parasiticus. All CDs suppressed the proliferation of both pathogenic and spoilage bacteria; however, high MIC values indicated the limited antibacterial effectiveness. CDs up to 500 mg/L maintained cell viability greater than 80% towards normal BJ cells. When SA-CDs (500 ppm) were incorporated into peeled and deveined Pacific white shrimp (Litopenaeus vannamei), lipid peroxidation during 10 days of refrigerated storage was retarded, as evidenced by lower PV, TBARS, and greater PUFA retention than the control and ascorbic acid-treated samples. Heat map and PCA analyses revealed that lipid oxidation was governed by CD type and storage time.