Microencapsulation of lemongrass oil by spray drying: Role of emulsion size, oil loading, and inlet air temperature on flavor retention and release kinetics

Abstract

Microencapsulation of lemongrass oil using modified starch (Capsul®) was investigated via spray drying to interpret the process–structure–transport relationships governing flavor retention and release. The effects of oil loading, emulsion size, and inlet air temperature on emulsion characteristics, citral retention, powder morphology, and stability were evaluated. Increasing oil content resulted in larger emulsion droplets, reduced emulsification efficiency, and greater surface oil content, leading to lower citral retention. Capsul® demonstrated high encapsulation performance, retaining up to 40 wt% lemongrass oil with minimal losses. Emulsion droplet size emerged as a key structural determinant, with smaller droplets yielding superior retention and reduced surface oil. By integrating microstructural analysis with kinetic modeling, this study demonstrates that drying-induced particle architecture, rather than retention efficiency alone, governs long-term stability. Release profiles were well described by Avrami kinetics, confirming diffusion-controlled transport, with larger droplets and higher oil loading exhibiting increased effective diffusivity. Although inlet air temperature had minimal influence on immediate citral retention, it strongly affected powder microstructure: higher temperatures produced larger particles with thinner walls, whereas temperatures below 140 °C increased residual moisture, lowered glass transition temperature, and accelerated volatile release. These findings provide mechanistic guidance for the rational design and optimization of spray-drying processes to tailor the stability and release performance of encapsulated flavor systems.