School of Agricultural Technology, King Mongkut’s Institute of Technology Ladkrabang, Bangkok, 10520, Thailand
Abstract
Plant essential oils have limited water solubility, for which problem oil-in-water emulsions provide a good solution. The aim of this work was to prepare a ginger essential oil (Zingiber officinale Rosc.; GEO) coarse emulsion, microemulsion, and nanoemulsion all with the same formula, determine their characteristics, and compare their antioxidant activities and utility as holding solutions for Davallia fronds. A coarse emulsion was firstly formed by a magnetic stirrer of GEO with a 1:2 by weight mixture of Tween 20 and Span 20 at weight ratio of 1:8, respectively. The coarse emulsion droplets (810.0 nm) were then broken by sonication and high-pressure homogenization to create the microemulsion (426.1 nm) and nanoemulsion (76.4 nm), respectively. The three emulsions exhibited V-potential values more negative than -30 mV, indicating them to be stable. All three emulsions demonstrated DPPH• and ABTS•+ free radical scavenging capacities significantly higher than those of GEO in ethanol. Meanwhile, the nanoemulsion significantly improved the Fe2+ chelating effect Finally, in a bioefficacy experiment with Davallia fronds, both the microemulsion at concentrations of 5 and 10 mg/mL and the coarse emulsion at 10 mg/mL were found to extend frond vase life. The nanoemulsion demonstrated superior frond longevity at low concentration (5 mg/mL), but at higher concentration (10 mg/mL), vase life and leaf chlorophyll were not improved and malondialdehyde formation increased. Based on the current investigation, emulsification significantly enhances the antioxidant activities of GEO. Vase solutions containing high concentrations of coarse emulsion (10 mg/mL), microemulsion (5 and 10 mg/mL), and low concentration of nanoemulsion (5 mg/mL) increased Davallia frond longevity from 6.3 days to up to 11.9 days. Our findings suggest that there is an optimal concentration range for using essential oil emulsions in different delivery systems as a preservation solution in cut fronds.
