Biomass-derived photoluminescent carbon quantum dots for preservation and smart quality monitoring of apple juice.

Anthocyanin (An)-derived carbon quantum dots (CQDs) with intrinsic biological activity and photoluminescence (PL) sensing capacity were employed for the first time in a sustainable multimodal approach for simultaneous biopreservation and real-time freshness monitoring of spoilage-associated changes of apple juice. An extracted from spent calyces of Hibiscus sabdariffa (roselle) served as a sustainable well-defined precursor for CQDs synthesized via a one-step hydrothermal method. AnQDs demonstrated enhanced antioxidant, antimicrobial activity against foodborne pathogens, and low to negligible cytotoxicity toward normal lung fibroblasts, maintaining cell viability between 83.0 and 94.60%. pH-resolved zeta potential reflected a correlation between surface ionization and pH, whereas excitation-dependent emissions of AnQDs, coupled with mathematical correlations of PL intensity with pHs (1-14) and temperatures (30-70 °C), offered valuable insights for their reliable sensing potential in food systems. Incorporation of AnQDs into chitosan (CS) optimized the hydration/barrier/thermal performance of the emerging smart film strips (SFSs), positioning them as viable candidates for active/smart food packaging. Addition of AnQDs (0.40 mg/mL) to artificially contaminated apple juice eradicated Rhodotorula mucilaginosa populations after 6 days of storage at 7 ± 2 °C and preserved key quality parameters, supporting their promising use as a natural "stand-alone" preservative that can reduce the reliance on conventional chemicals. The SFSs delivered immediate (1-2 min) PL response to spoilage progression upon excitation at 365 nm, with a limit of detection as low as 3.01 CFU/mL for Rhodotorula according to the experimental settings. The strong linear correlation between PL intensity of the SFSs and pH changes in artificially contaminated juice throughout storage, enabled a reliable estimation of the time at which the established spoilage threshold was reached. This proof-of-concept study provides preliminary evidence supporting the potential of smart AnQDs as a multifunctional platform for non-thermal biopreservation of apple juice, while the developed SFSs offer a rapid, cost-effective, and non-destructive means of freshness assessment under abusive refrigerated storage. The data warrants further validation of the SFSs in additional juice models to monitor quality changes induced by other foodborne pathogens associated with juice spoilage and outbreaks and encourages extending their application in food matrices susceptible to alkaline spoilage by leveraging the multifunctionality and tunable photoluminescence (PL) properties of AnQDs.