Electrospinning of polymer-free cyclodextrin/geraniol-inclusion complex nanofibers: enhanced shelf-life of geraniol with antibacterial and antioxidant properties
Free-standing nanofibrous webs of cyclodextrin/geraniol-inclusion complex (CD/geraniol-IC-NF) showing antibacterial, antioxidant activity and slow release of geraniol were developed as flavour/fragrance releasing materials via electrospinning. The electrospinning of CD/geraniol-IC-NFs with uniform and bead-free morphology was achieved without using a polymer matrix. Three types of CDs modified with hydroxypropyl and methyl groups (HPβCD, MβCD, and HPγCD) were used to obtain CD/geraniol-IC-NFs. The polymer-free CD/geraniol-IC-NFs allow us to attain much higher geraniol loading (∼11%, w/w) when compared to electrospun polymeric nanofibers containing CD/geraniol-IC (∼5%, w/w). Geraniol has a volatile nature, yet, a significant amount of geraniol (∼60-90%) was preserved in CD/geraniol-IC-NFs due to the complexation, whereas evaporation of geraniol was unavoidable for polymeric nanofibers incorporating geraniol without cyclodextrin. Short-term (3 h) temperature dependent release (37 °C, 50 °C, and 75 °C) and long-term open air (50 days, at RT) release tests revealed that MβCD/geraniol-IC-NF released less geraniol compared to HPβCD/geraniol-IC-NF and HPγCD/geraniol-IC-NF, indicating that much stronger inclusion complexation was formed between MβCD and geraniol. The release of geraniol from CD/geraniol-IC-NFs prevented the colonization of Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria to a great extent, as observed in the antibacterial activity results. It was observed that CD/geraniol-IC-NFs had higher antioxidant activity compared to pure geraniol due to the solubility increase. In brief, the results reported here may open a new door to enhance the performance of essential oils and flavour/fragrances, to preserve volatile compounds from evaporation and to better understand the potential of CD/IC-NFs as carrier systems for guest compounds in the food, cosmetic and household cleaning industries.