CS/N-CD composites enhance physical barriers, antioxidant activity and microbial modulation for improved chili pepper preservation

Abstract

Chili peppers (Capsicum annuum L.) have a high postharvest metabolism, causing moisture loss and microbial spoilage, which shortens their shelf life, thereby imposing environmental burdens through resource waste, greenhouse gas emissions, and secondary pollution. Carbon dots (CDs), zero-dimensional carbon-based nanomaterials with particle sizes below 10 nm, show promise in food packaging and postharvest preservation. In this study, a chitosan/N-CD (CS/N-CD) composite material was developed with superior barrier, antioxidant activity, and antibacterial properties. CS/N-CD films with different N-CD ratios showed good compatibility, enhanced UV absorption, improved barrier properties (0.5% film with 11.4% lower WVP), and higher antioxidant activity (2.5% film with 66.8% DPPH scavenging). The 0.5% films showed high antibacterial rates against Escherichia coli and Staphylococcus aureus (89.2–99.6% vs. 14.9–62.5% for pure CS). After being applied to chili pepper fruits via spraying, dipping, and film-coating, the material reduced weight loss and preserved fruit firmness (2.5-fold reduction by day 21 vs. 4.8-fold for the control). High-throughput 16S rRNA gene sequencing showed that CS/N-CDs altered the microbial structure; dipping increased Actinobacteria by 355.4% and suppressed Enterobacter by 98.2%, while spraying reduced Enterobacter by 82.9% and enriched Pseudomonas by 87.1%, thereby improving the microbial microenvironment during storage of the chili pepper fruit. These results show that the CS/N-CD composite exerts a synergistic preservation through a physical barrier and microbial modulation. Given the eco-friendly properties of CS/N-CDs, these findings offer insights into advancing sustainable nanocomposite-enabled postharvest preservation.