Fabrication and characterisation of vegetable chitosan derived microcapsules

Baiocco, Daniele (2022). Fabrication and characterisation of vegetable chitosan derived microcapsules. University of Birmingham. Ph.D.

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Abstract

Microencapsulation is a highly effective technology to deliver value-added actives at end-use applications, such as in food, personal care, and detergent products. The goal of the present research was to develop a novel microencapsulation system to encapsulate perfume/flavour oils by complex coacervation using plant-based biopolymers. Complex coacervation entails the electrostatic interplay between pairs of polymers carrying opposite charges. Specifically, this research was aimed towards: (i) investigating the feasibility and the experimental conditions required to induce complex coacervation between fungal chitosan (fCh) and gum Arabic (GA); (ii) determining the optimum fabrication conditions of fCh-GA complexes including pH and the weight ratio of GA-to-fCh based on their electrokinetic charge and turbidimetric analysis; (iii) developing methodologies for encapsulating perfumes (i.e. hexylsalicylate) and food flavour (i.e. L-carvone) oils within a safe fCh-GA shell via complex coacervation; (iv) understanding the physico-chemical, structural, surface topographic, mechanical, and barrier properties of the resulting plant-based microcapsules using several analytical techniques, such as scanning (SEM) and transmission electron microscopy (TEM), micromanipulation, UV-Visible spectrometer, and Fourier-transform infrared spectroscopy (FT-IR).

The electrokinetic analysis of fCh and GA revealed that complex coacervation was optimised at a GA-to-fCh weight ratio approximately equal to 7:1. The interactions of the biopolymer pair was examined as a function of pH (1.0~8.0), which enabled to identify their complex coacervation comfort zone (CCCZ) as well as critical turbidity zone (CTZ). The optimised pH was 3.4, which triggered the strongest electrostatic attraction between fCh and GA. The stability of oil-in-water emulsions was investigated via interfacial tension analysis, which included the use of sorbitan esters (Spans), polysorbates (Tweens), and their combined adducts as the stabilising agents. Under the above conditions, microcapsules with a plant-based shell and a core of value-added oil were produced. Elongated as well as spherically shaped microcapsules could be fabricated conditionally upon the stirring rate during coacervation. Surface topography by SEM revealed well sealed microcapsules with a core of oil. The mechanical properties of microcapsules were determined via a micromanipulation technique.

The rupture force and nominal rupture stress of perfume oil microcapsules were 2.0±0.1 mN and 3.6±0.3 MPa, respectively, which are comparable to those of commercially available melamine formaldehyde (MF) based microcapsules. In-depth shell thickness analysis on the resulting microcapsules was performed by TEM. The results were used to validate the predicted shell thickness of microcapsules using experimental micromanipulation data combined with the simulation results of finite element analysis (FEA), which also enabled to quantify the intrinsic material property parameter (i.e. Young’s modulus of the shell material). The oil leakage tests were carried out to assess the barrier properties of the microcapsules. Furthermore, the oil leakage data were fitted to a solute-diffusion model, which allowed to estimate the shell permeability.

As a further step towards developing highly versatile cutting-edge microencapsulation systems with a potential application in food industry as well, several formulation modifications were made to encapsulate L-carvone. The introduction of a two-stage microencapsulation process (i.e. complex coacervation followed by spray drying) allowed to achieve food grade free-flowing powders with a load of L-carvone, which proved stable for over a month.

Overall, the results evidenced that perfume/flavour oil microcapsules within a safe plant-based shell could be fabricated via complex coacervation. Moreover, the fCh-GA system has shown to be a promising carrier for the encapsulation of fragrance/flavour ingredients, which presents a new opportunity to globally overcome cultural and religious concerns associated with animal sourced products.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):