Carbon dots from tuna stick water doped with phenolic acids: Structural, optical, and physicochemical properties with enhanced antioxidant and antimicrobial activities.

Tuna stick water, a major effluent from canned tuna processing, has not been fully valorized, especially as functional carbon dots (CDs). This study addresses the conversion of this effluent into CDs doped with food-grade phenolic acids (gallic acid, GA; tannic acid, TA) at concentrations of 0.1-0.5% (w/v) via hydrothermal synthesis. Structural analysis confirmed integration of carbonized phenolic moieties, enriching surface functional groups. Spherical and quantum-sized (2.5-12.5 nm) CDs exhibited enhanced physicochemical and functional properties, particularly upon TA-doping. Crucially, 0.5% TA-doped CDs exhibited broad-spectrum antimicrobial activity against foodborne pathogens (Staphylococcus aureus and Vibrio parahaemolyticus; minimum inhibitory concentration (MIC): 1.7 mg/mL) and spore-producing fungi (Aspergillus flavus MIC: 13.2 mg/mL), demonstrating lower MIC than undoped CDs. Antioxidant capacity was significantly enhanced, especially ABTS-radical scavenging (65.87 mmol Trolox-equivalent/mg) and metal-chelation (2.37 mmol EDTA-equivalent/mg). This approach transforms food waste into a functional nanomaterial for food preservation, contributing to waste valorization and food safety.