Designing and Characterization of Emulsion-Based Matrices for the Encapsulation of Bioactive Oils using Polysaccharides

Abstract

Flaxseed oil has abundant polyunsaturated fatty acids that are important to health but are oxidized easily during storage. These bioactive lipids are susceptible to chemical deterioration causing nutrient loss and development of undesirable off-flavors. Oil-in-water emulsions could be used as an effective tool to protect these functional active lipids from degradation by engineering the emulsion droplet interfacial layer. Engineering oil/water interfaces of emulsions has been studied extensively, but practical technologies are still demanded by the food industry. Emulsions are a category of encapsulation systems applicable to various bioactive compounds in food formulations. Emulsions have a fluidic oil phase which facilitates the mobility and release of bioactive compounds. Emulsion based encapsulation systems has been exhibited to have potential applications in functional food formulation. They have been used to inhibit lipid oxidation, triggered or controlled release during different processing and storage conditions. Biopolymer characteristics (e.g., molecular weight, charge density, and conformation) and droplets characteristics (e.g., size, charge, and concentration) are most significant aspects in the formulation of stable emulsions.
In this study natural biopolymer pectin and chitosan has been used to produce oil-in-water emulsions. In first part of study, primary emulsion was produced from pectin and influence of sonication time, pH, NaCl, surfactant to oil ratio was studied. It was found that pectin emulsion at a pH primarily had less charge density and then changing the pH conditions to where they had more charge density (4.0 to 8.0) led to the development of less stable primary emulsion. The pectin layered droplets in the primary emulsions were stable to creaming and droplet aggregation at temperatures at 100 ºC and NaCl concentrations up to 120 mM. However, droplets were more prone to instability due to coalescence at less pectin concentration.
In the next part of the thesis, bi-layered emulsions were created using layer-by-layer approach. Pectin was used to stabilize a primary emulsion with less droplet size, then, a cationic chitosan biopolymer was coated to the primary emulsion to produce secondary emulsions with cationic charge around the droplet. The interface of pectin and chitosan as a function of pH, NaCl and biopolymer concentration was studied with the anticipation of drawing conclusion for their interaction at droplets surfaces. Chitosan and pectin interaction to form insoluble or soluble polyelectrolyte complex at the droplet interface was dependent on the pH. At pH conditions where chitosan and pectin have opposite droplet charges (pH 3.5, 4.0 and 5.0) they interact intensely to form polyelectrolyte complexes. Stable and tailored pectin-chitosan secondary emulsions however could be formulated. But, confined range of chitosan concentration (between depletion concentrations and saturation) and protonation of chitosan are important factors in preparation of pectin-chitosan bi-layered emulsion.
The objective of this research was therefore to understand how emulsion interface properties and interactions among emulsion droplets influence lipid oxidation in food emulsions. In addition, this study delivers valuable evidence on practice of the layer-by-layer approach for production of bi-layered food grade emulsions with an emphasis on the effects of formulation conditions and biopolymer properties on long term emulsion stability.