Natamycin-loaded zein nanoparticles stabilized by carboxymethyl chitosan: Evaluation of colloidal/chemical performance and application in postharvest treatments

In this study, the natural fungicide natamycin (N) was encapsulated in zein/carboxymethyl chitosan core-shell nanoparticles (Z/CMCS NPs) to improve its aqueous dispersibility and photostability for application in postharvest fruit preservations. The N-Z/CMCS NPs were spherically shaped with a particle size of 223 ± 2 nm, a polydispersity index of 0.07 ± 0.01 and a surface charge of −50.7 ± 2.3 mV. The NPs were characterized by FTIR spectroscopy and scanning electron microscopy. The encapsulation efficiency of natamycin was improved from 68.3 ± 2.4% to 78.4 ± 1.7% by the addition of CMCS to the NPs. The optimized N-Z/CMCS NPs remained stable and were resistant to neutral pH (6.0–8.0), ion strength (0–100 mM) and long-term storage (30 days). The degradation of natamycin under UV light was reduced, with a half-life time (t1/2) of 47.2 min in the pure state to a t1/2 of 147.5 min in the N-Z/CMCS NPs. The stabilized N-Z/CMCS NPs retained the property of redispersibility after freeze-drying. The bacteriostatic properties of N-Z/CMCS NPs against Botrytis cinerea were tested in vitro and in vivo. The in vitro results demonstrated that the application of N-Z/CMCS NPs completely inhibited the spore germination rate, and 10 mg/L N-Z/CMCS NPs inhibited the mycelial growth by 64.4%. The in vivo results indicated that the NPs not only reduced the occurrence of rot and mildew in inoculated strawberries, with the lowest decay index of 30.3% after 3 days storage, but also inhibited the occurrence of gray mold disease in postharvest strawberries, with the lowest decay rate of 31.1% after 8 days of storage. This study will be beneficial for the development of colloidal delivery systems for postharvest fruit industries.