Citral encapsulation in plasmolyzed yeast cells increases loading and reduces initial burst release while extending...

Citral repels Haemaphysalis longicornis nymphs, but its volatility limits persistence. This study compared citral-loaded Saccharomyces cerevisiae formulations prepared with or without plasmolysis-associated pretreatment for recoverable citral-equivalent content, empirical release behavior, and repellency.

Yeast was incubated in 10% (w/v) NaCl at 50 °C for 48 h and heated at 80-85 °C for 20 min before citral loading. Plasmolyzed microcapsules (P-C) contained more UV-recoverable citral-equivalent material than non-plasmolyzed microcapsules (NP-C) (35.5 ± 3.3% versus 24.3 ± 2.4%; n = 3, P < 0.05). Confocal images and line scans showed stronger, more uniform cell-associated Nile red fluorescence in P-C, but localization was qualitative and did not distinguish intracellular from surface-associated material. Fourier transform infrared spectra retained citral-related bands, although matrix overlap precluded compound-specific confirmation and exclusion of minor oxidized species. In 30:70 v/v water/ethanol, NP-C was better fitted by a burst-adjusted first-order model, whereas P-C was better fitted by a modified Higuchi-type model; therefore, no common or diffusion-controlled mechanism was established. The modified Higuchi apparent burst parameter was lower for P-C than for NP-C (0.119 versus 0.324). In silicone membrane choice assays, pure citral was significantly repellent at 3 h but not at 4 or 5 h, whereas P-C remained significantly repellent at 5 h.

P-C showed higher recoverable citral-equivalent content, more uniform cell-associated fluorescence, lower apparent early release, and significant 5-h repellency. However, activity beyond 5 h, residual citral at 5 h, vapor-phase exposure, and compound-specific integrity were not determined. Interpretation was conservative because UV detection was not chromatographically validated for specificity. © 2026 Society of Chemical Industry.