Enhanced water-barrier carboxymethyl cellulose coatings reinforced with grapeseed oil and cellulose nanofibers for blueberry preservation

The extreme perishability of blueberries accelerates the loss of key nutritional and flavor characteristics. Here, polysaccharide-based coatings of carboxymethyl cellulose (CMC), grapeseed oil (GSO) at varying concentrations (0-0.1w/w%), and cellulose nanofibers (CNF) of different sources were developed to enhance the water barrier of polysaccharide-based coatings for blueberry preservation. CNF formed strong interactions with CMC polymer chains, producing a dense matrix, functioning as nanofillers to increase water diffusion tortuosity and serving as oil carriers to enhance coating hydrophobicity. The different CNF characteristics were correlated with film properties and fruit preservation efficiency, comparing CNF with a lower aspect ratio, obtained from spent coffee grounds (SCG), to CNF with a higher aspect ratio and purity from a bacterial (BCNF) origin. BCNF-containing coatings, particularly CB-0.1 (CMC/BCNF/GSO-0.1w/w%), demonstrated optimal fruit preservation, revealing the slowest fruit deterioration, with up to 18% lower decay rate compared to uncoated, maintaining fruit quality for up to 12 days under accelerated storage conditions, showing a potential to reduce postharvest losses. The higher aspect ratio of BCNF provided more interaction sites and fiber entanglement, resulting in improved compatibility with the CMC matrix, enhanced oil droplet stability, a more cohesive coating structure, and superior barrier and mechanical performance compared with SCG-CNF-based films. Cryo-SEM analysis revealed compatibility of CB-0.1 coating on the blueberry surface, forming an additional protective layer while preserving the external bloom, contrary to SCG-CNF-coating, which penetrated and disrupted the bloom. This work presents a tunable blueberry preservation approach, whereby CNF properties can be adapted to suit different fruit physiologies.