Synergistic reinforcement of chitosan coating films by Haematococcus pluvialis residue-derived protein and carbon dots for active food packaging.

Haematococcus pluvialis defatted residue (HPR), an underutilized byproduct of astaxanthin extraction, was valorized into dual-functional components, HPR-derived protein (HPRP) and carbon dots (CDs). These were synergistically incorporated into a chitosan (CS) matrix to develop active coating films. The CDs (2.45 nm) exhibited abundant oxygen/nitrogen functional groups, imparting potent antioxidant and antibacterial activities. Co-incorporation of HPRP and CDs induced a dense, cooperative polymer network through intensive hydrogen bonding and electrostatic interactions. Notably, the CS/HPRP/2%CDs film displayed optimal physicochemical performance with maximum tensile strength (10.84 MPa), reduced water vapor permeability, and improved CO₂/O₂ selectivity compared to CS alone. Furthermore, the composite film showed outstanding UV-blocking and antibacterial efficacy (>95% against E. coli and S. aureus). Practically, the coating effectively reduced weight loss and microbial growth, maintaining the firmness and quality of Red Globe grapes. This provides a sustainable route for utilizing microalgal waste in advanced active food packaging.