Active sweetpotato peel nanomaterial/sodium alginate coatings containing carnauba wax and propolis extract for preserving strawberry quality.

Abstract

This study presents multifunctional edible nanocoatings from sweetpotato peel nanomaterial (SPPnm) and sodium alginate (SA) incorporating carnauba wax and ethanolic propolis extract (EPE) to improve strawberry postharvest preservation. Carnauba wax was incorporated at 0, 0.5, 1.0, and 3.0% (w/v), while glycerol, Tween 80, and EPE were used as a plasticizer, emulsifier, and natural antimicrobial agent, respectively. The SPPnm showed irregular fibrillar and particulate morphology, supporting its function as a lignocellulosic reinforcing phase in the alginate matrix. Structural, morphological, rheological, wettability, mechanical, oxygen-barrier, and antimicrobial analyses confirmed the physical integration of wax and EPE within the SPPnm/SA network. All coating suspensions exhibited shear-thinning behavior suitable for dip coating. Wax incorporation increased film hydrophobicity, with the initial water contact angle increasing from 40.7° for the wax-free film to 80.5° for the 1.0% wax film. In contrast, 3.0% wax caused phase separation, cracking, and poor film continuity. The EPE-loaded films showed concentration-dependent antibacterial activity against Listeria monocytogenes and Salmonella enterica. For the strawberry coating application, the formulation reduced the weight loss and respiration rate. It also improved firmness retention and maintained titratable acidity, total soluble solids, pH, and ripening index compared with the uncoated one. The 1.0% wax formulation provided the best balance between film integrity, hydrophobicity, antimicrobial functionality, and postharvest quality preservation, demonstrating the potential of SPPnm-based coatings as sustainable active coating materials for highly perishable berries.