Advancing flavour/fragrance oils microencapsulation: exploring the impact of core oil on microcapsule characteristics

Huang, Qun (2024). Advancing flavour/fragrance oils microencapsulation: exploring the impact of core oil on microcapsule characteristics. University of Birmingham. Ph.D.

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Abstract

The aim of the project is to develop simple, industrially scalable encapsulation methods to fabricate biodegradable microcapsules with desirable properties, using either natural waxes by melt dispersion or gelatine/gum arabic by complex coacervation.

L-carvone (LC) and hexyl salicylate (HS) were used as model core oils. Core oils are encapsulated based on the formation of wax microspheres, while addressing the influence of different types of waxes as well as different oil to wax ratios. HS encapsulation efficiency (EE) ranging from 75.7 ± 2.7 to 83.7 ± 1.2 % has been achieved for different types of waxes, which were comparable to those of commercially available melamine formaldehyde (MF) based microcapsules (EE, 75%), and higher than the recently developed microcapsules (EE, 47 ± 11%) using plant-based biopolymers (Chitosan and gum arabic). The Young’s modulus of each wax microspheres determined by the Hertz model had a wide range of values from 28.3 ± 1.4 to 390.7 ± 16.0 MPa, suggesting the availability of wax microspheres for various industrial applications. Moreover, the desirable properties of wax microspheres could be controlled by selecting a certain oil to wax ratio.

Also, gelatine/gum arabic coacervate based microcapsules have been fabricated to encapsulate L-carvone, limonene and hexyl salicylate via complex coacervation. The highest EE (89.0 ± 1.2%) was achieved for HS loaded microcapsules. Their mean apparent Young’s modulus of microcapsules was determined by the Hertz model (668 ± 165 MPa) and the intrinsic Young’s modulus of microcapsules shell was determined
by finite elements analysis (6.2 ± 1.0 GPa). Both the EE and mechanical properties were significantly higher than those of chitosan/gum arabic or commercially formaldehyde-based microcapsules, suggesting the feasibility of gelatine/gum arabic to be utilised in applications for household care, laundry and textile industries. However, LC was not encapsulated well by gelatine/gum arabic microcapsules (EE, 5.0 ± 0.4 %) compared to HS (EE, 89.0 ± 1.2%), evidencing the significant influence of core oil on microcapsule characteristics.

Finally, the physical properties of core oil (linalool, L-carvone, limonene, hexyl salicylate, carvacrol and cinnamaldehyde) were examined in order to evaluate their effects on the capsule morphology and encapsulation efficiency by combining the spreading coefficient and two component surface energy theories. It was found that the spreading coefficient configurations (based solely on thermodynamic considerations) for each oil did not give an accurate prediction of capsule morphology when high molecular weight biopolymers (gelatine/gum arabic) were involved in the system. However, the predicted structural morphology for different oil microcapsules were still holistically consistent with their encapsulation efficiency, which also was found to increase with the decreasing surface polarity of the core oil.

Overall, although wax microspheres and gelatine/gum arabic coacervated microcapsules did not give satisfactory EEs for the encapsulation of LC, the performances (high EE and strong mechanical strength) of these microspheres and microcapsules containing HS looked promising. The impact of both thermodynamic spreading coefficients and surface polarity of each core oil on the formed microcapsule structural morphology and encapsulation efficiency is crucial, providing a useful insight about the engulfing mechanism for oil encapsulation both for academic research and industrial applications.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):