Abstract
Essential oils have been widely used as an active ingredient in mosquito repellent products. However, essential oils are highly unstable and prone to degradation when exposed to the environment during storage. Microencapsulation techniques help to maintain the stability of molecules in essential oils that are sensitive to environmental stress, and therefore improve shelf life. In this study, the physical stability and efficacy of a repellent formulation consisting of encapsulated Citrus grandis essential oil (CGEO) were evaluated under different storage conditions over a 12-month period by comparing the formulation with a non-encapsulated formulation. The formulations were both stored under two different storage conditions, i.e., 25 ± 2 °C/60% ± 5% relative humidity (RH) and 40 ± 2 °C/75% RH ± 5%, for 12 months. Droplet size, zeta potential, and pH value were measured after 1, 6, and 12 months of storage to determine their stability. For the study of efficacy, each formulation was tested against Aedes aegypti under laboratory conditions. We found that the microencapsulated formulation’s physical characteristics showed insignificant changes as compared with the non-encapsulated formulation during storage. The microencapsulated formulation demonstrated better repellent effects, sustaining high protection (>80%) for 4 more hours of exposure after 12 months of storage as compared with the non-encapsulated formulation that demonstrated high protection for only an hour post application. Microencapsulation helped to preserve the stability of the formulation, which resulted in high protection being maintained for over 12 months of storage.
Highlights
Essential oils are the secondary metabolites produced and stored in the secretory glands of aromatic plants [1,2]
The suspension of semisolid microencapsulated Citrus grandis essential oil (CGEO) presented as a milky white liquid with no essential oil observed either on the surface of the suspension or after centrifugation of the discarded aqueous supernatant
Marked encapsulation application in plant-based repellent product development helped to improve the stability and efficacy of the formulation, which were successfully observed in this study
Summary
Essential oils are the secondary metabolites produced and stored in the secretory glands of aromatic plants [1,2]. They play an important role in a plant’s defensive mechanisms against fungi, pathogenic microorganisms, herbivores, and insects [3]. Due to these functions, essential oils are widely used in the medicinal, pharmaceutical, cosmetics, as well as pesticide and insecticide industries [4]. In particular, plant extracts are extensively used as active ingredients in repellent products, which are receiving more attention from consumers than the synthetic repellents. Nowadays, customers are keen to choose plant-based repellents to protect themselves against mosquito bites [5]
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