Co-Encapsulation oF Fish Oil With Phytosterol Esters And Limonene

Abstract

Lipophilic bioactive components (LBCs) including fish oil, phytosterols, and limonene, have beneficial effect on human health. However, their hydrophobic nature and susceptibility to oxidation, light and heat limit their application in most food systems. The aim of this study was to develop a stable delivery system in microcapsule form for LBCs, especially fish oil, by coencapsulation with phytosterol esters (PE) and limonene using food-grade emulsifiers. As the first step, formation of the emulsion was studied to obtain a stable and submicron-size emulsion system. This was achieved by studying the effect of homogeniser conditions, types and composition of emulsifier, solid content and oil/emulsifier ratios on the physicochemical properties and stability of the fish oil emulsions. Milk proteins including whey protein isolate (WPI) and sodium caseinate (NaCA) were studied as they were reported to have surface active properties and excellent oxygen barrier. Results show that WPI was more suitable to be applied as the main emulsifier in current research than NaCA, since its solubility was not influenced by pH. WPI could also be applied at high concentration due to its low viscosity. Mixed WPI and NaCA in a ratio of 4:1 and WPI and soluble corn fiber (SCF) in a ratio of 1:1 produced submicron emulsions with high stability. The combination of emulsifiers including maltrodextrins DE 10, DE 18, and gum Arabic could not give stable and monomodal distribution emulsions. A physical blend of WPI with SCF or NaCA together in water was the best order of addition preparation of emulsion with high stability and good properties. The order of lecithin addition, either in an aqueous or oil phase, did not show any positive effect on the emulsion properties and stability. The oxidative stability of fish oil was promoted by emulsification and was further improved by the addition of phytosterol esters. Fishy odour was successfully masked by the incorporation of limonene in the formulation. Based on the results of emulsion properties, a composition of 75 % fish oil, 12.5 % phytosterol esters and 12.5 % limonene was chosen as the composition for the oil phase. The microstructure of selected emulsions was studied by small angle x-ray scattering (SAXS). Results revealed that the emulsions had a large polydisperse spherical structure at the droplet interface and dispersion of small polydisperse spheres in solution. The emulsions stabilized by different emulsifiers showed relatively different structures at the interface while various forms and size of free emulsifiers were presented in solution. To some extent, the different microstructures of the emulsions reflect differences in properties and stability. Secondly, the emulsion systems with optimum properties and stability were dried into powder form using spray drying and freeze drying methods. Physicochemical properties of microcapsules, including water activity, glass transition temperature, microencapsulation efficiency and microstructure were investigated after the drying processes. Storage stability and in vitro digestibility of microcapsules were also investigated. Results from the physicochemical properties of microcapsules show that spray drying was the more suitable method for drying the emulsions compared with freeze drying. The spray dried microcapsules also had higher retention of limonene and lower formation of limonene oxide during storage. Among the spray-dried samples, the samples containing mixed milk proteins as wall materials gave slightly higher protection against oil oxidation compared with samples containing WPI and SCF. The results could be explained by the thicker interfacial layer around the oil droplets and the lower oxygen permeability of milk proteins. The study of interaction between wall components using Fourier Transform Infrared Spectroscopy (FTIR) revealed that as there was a shift of the amide II band, conjugates from a Maillard reaction possibly occurred in the protein and carbohydrate system during processing. This could be the reason that wall materials containing WPI and SCF had antioxidant properties and a slower release of oil during in vitro digestion. On application to the real food systems, including juice, ice cream and yoghurt, WPI/SCFmicrocapsules (containing the amount of 50 mg EPA+DHA per serve) showed similar properties to those samples formulated with the commercial product, namely ROPUFA® during storage. The results suggest that these newly developed co-encapsulated microcapsules would be well suited to a commercial product. Overall, this research showed that co-encapsulation of fish oil with PE and limonene can be achieved through drying. The microcapsules were shown to have reasonably good properties and could be applied in new food products.