Comparative structure-function analysis of two defatted microalgae proteins and application in chitosan-based active packaging films for Red Globe grape preservation

To promote the utilization of defatted microalgae residues, Haematococcus pluvialis and Nannochloropsis oculate, which widely cultivated for commercial extraction of high-value functional lipids, were selected in this study. The physicochemical and structural properties of proteins extracted from defatted residues were comprehensively compared, and their potential in constructing chitosan (CS)-based active packaging films was explored. Compared to NORP, HPRP possessed higher total amino acid content of 84.75 g/100 g protein, smaller particle size, stronger electrostatic repulsion, and highly flexible molecular chains, which conferred favorable compatibility with CS. Conversely, due to its higher structural rigidity characterized by elevated β-sheet content and surface hydrophobicity, NORP induced severe phase separation and macroscopic precipitation upon blending with CS. Based on this discrepancy, HPRP was selected to fabricate the CS/HPRP films, revealing that an appropriate amount of HPRP constructed a dense cross-linked network within the films through strong hydrogen bonding and electrostatic interactions, significantly enhancing the mechanical properties of films. Specifically, the tensile strength and elongation at break of CS/HPRP-1 reached 4.02 MPa and 87.57%, respectively, which also demonstrated superior UV-shielding properties with a UVA blocking rate of 95.89%, strong antioxidant activity, and superior CO₂/O₂ selectivity. In practical application, the CS/HPRP-1 coating effectively reduced water loss and non-enzymatic browning in Red Globe grapes, while maintaining fruit firmness and ascorbic acid content over 12 days of storage, thereby significantly delaying quality deterioration. This study elucidates the structure-function relationships of microalgae proteins and provides a sustainable strategy for developing high-performance food preservation materials from microalgae waste.