Wood hemicelluloses as wall materials to produce bilberry microcapsules: Wall composition determined by microspectroscopy During spray-drying microencapsulation, the core materials (bioactive compounds) are surrounded or entrapped within the wall material matrix (usually carbohydrate or protein biopolymers) which results in the formation of microcapsules. The tailored wall will protect the core material from the impact of heat during production and from other environmental stressors. The use of heterogenic polymers to microencapsulate the bioactive compounds-rich foods, can generate a complex structure of the microcapsules which adjusts the physicochemical properties of the initial materials (wall and core materials) such as solubility, digestibility, organoleptic and thermal properties. Understanding the composition of the designed microcapsule wall will enable the control of their functional properties which orients their applications in various food products. However, most of the current available methods and techniques to study microcapsules (e.g., food powders) are restricted to their surfaces and bulk composition. This is in turn resulted in difficulties to predict the microcapsule’s behaviour during long-term storage and/or their possible chemical modifications and applications. Therefore, there is a need to further understand the distribution/localisation of the components of the microcapsules wall. To address this issue, a new approach of applying advanced analytical techniques by adapting and modifying existing methods previously used to study complex materials structure (e.g., plant cell walls) is required. In my PhD project, I have used wood hemicelluloses, a by-product of forest industries, as new wall materials to design the microcapsule wall of spray-dried bilberry powders to produce a healthy and sustainable food ingredient. Wood hemicelluloses are heterogenic polymers consisting of sugar units, O-acetyl groups, and lignin-derived phenolic residues. Thus, the composition of bilberry microcapsules and/or their wall will include hemicelluloses, lignin (residues in hemicelluloses), phenolics (from both bilberries and hemicelluloses). Therefore, I must understand the distribution/localization of these components to further improve the functional properties and orient the applications of the microcapsules. To achieve these goals, I have planned a 3-month research visit to the Biomass Science and Technology Research Group (University of Copenhagen, Denmark) led by Professor Lisbeth Garbrecht Thygesen, who has more than 25 years of experience with wood materials with the scope of structural characteristics by using a range of spectroscopic and microscopic techniques. Under the supervision and help of Prof. Lisbeth, I will adapt and modify the existing method that has been used study wood cell wall structure to study the microcapsules wall composition by using confocal Raman microscopy (CRM) and confocal laser scanning fluorescent microscopy (CLSM) coupled to multivariate curve resolution alternating least square. The unique advantage CRM and CLSM is that the operator is allowed to optically section the sample at any desired plane to be able to study the sample compositions. The success in adaptation and modification of the analytical method will enable the modification and incorporation of microcapsules into various food products by valorising Finnish wood-based hemicelluloses and wild berries. Following the same principle, there is a high possibility that the modified method could be applied to characterise different types of biopolymers in food formulations, pharmaceutical and cosmetic industries.

2023