γ-Cyclodextrin-Encapsulated Cinnamaldehyde for Citrus Preservation and Its Potential Mechanisms against Penicillium digitatum

In this study, a γ-cyclodextrin-cinnamaldehyde inclusion compound (γ-CDCL) was prepared to control green mold caused by Penicillium digitatum (P. digitatum) in citrus. The results showed that the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of γ-CDCL against the mycelial growth of P. digitatum were 2.0 g L(−1) and 4.0 g L(−1), respectively. Simultaneously, eight × MFC γ-CDCL could effectively reduce the incidence of green mold in citrus fruit without impairment of the fruit qualities, meanwhile, eight × MFC γ-CDCL was comparable to Prochloraz in controlling fruit under natural storage conditions. The structure of γ-CDCL was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) analyses. Results showed that the successful preparation of γ-CDCL was due to the spatial interaction between H-4,8 of cinnamaldehyde and H-5′ of γ-cyclodextrin. Meanwhile, the cell membrane permeability of P. digitatum was impaired by γ-CDCL through massive accumulation of reactive oxygen species, whereas the cell wall integrity was barely affected. These results indicated that γ-CDCL might inhibit the growth of P. digitatum through a membrane damage mechanism and it is a promising alternative to chemical fungicides in controlling the post-harvest citrus decay.