Microencapsulation of D-limonene through non-covalent coacervates of hemp protein isolate and gum Arabic

This study explores the impact of pH range and optimal pH (pH_opt) for complex coacervation on the properties of microcapsules containing D-limonene. An oil-in-water emulsion stabilized by coacervates formed from hemp protein isolate (HPI) and gum arabic (GA) was used. The total biopolymer concentration was fixed at 1.2 % (1 % HPI, 0.2 % GA), with core-to-wall ratios from 1:1 to 1:4. Coacervation occurred within pH 2.0–5.0, with pH 3.0–4.0 identified as optimal. Rheological analysis showed higher storage (G′) than loss (G″) moduli, indicating gel-like behavior. Formulation F₄ achieved the highest yield at 64.06 %, while F₉ had the lowest at 45.44 %, indicating variation in spray-drying efficiency across samples. The highest pay load of D-limonene (44.21 %) was observed for F₄, whereas F₉ had the lowest pay load of 12.51 %, and encapsulation efficiency also peaked for F₄ (88.05 %), with F₇ showing the lowest (62.03 %). Water activity remained low in all samples (0.14–0.20), with F₂ having the lowest (0.14) and median particle sizes ranged from 6.23 μm (F₃) to 7.39 μm (F₁), reflecting moderate variation in droplet size. Morphological differences among microcapsules formed at pH 3.0, 4.0, and 7.0 showed significant influence of pH on structure. Samples F₁–F₃ showed strong fluorescence due to higher oil content and more defined microcapsule structures while, the FTIR confirmed the involvement of non-covalent interactions during coacervation. The release of D-limonene followed diffusion-controlled kinetics (Weibull, b < 1). This work supports the development of natural, biodegradable systems for controlled release of volatile compounds in food, pharmaceutical, and cosmetic applications.