Encapsulation of omega fatty acid-rich oils using plant protein-based matrices
Oils rich in omega fatty acids (e.g., omega-3, -6, and -9) are both economically and nutritionally important to human beings, as they are playing significant roles in the prevention of various diseases (e.g., coronary artery disease, hypertension, and diabetes) and maintenance of mental health. However, due to their unsaturated nature, susceptibility to oxidation, and immiscibility in aqueous products, microencapsulation was introduced to entrap the oils to circumvent these challenges. The overall goal of this thesis was to encapsulate omega fatty acid-rich oils (e.g., canola, fish, and flaxseed oils) using plant protein-based (e.g., pea, soy, lentil, and canola protein isolates) matrices, in order to enhance storage stability. In study one, the effect of pH (e.g., 3.0, 5.0, and 7.0) on the physicochemical (e.g., surface charge, hydrophobicity, and solubility), interfacial (e.g., interfacial tension and rheology), and emulsifying (e.g., droplet size and emulsion stability) properties of pea, soy, lentil, and canola protein isolates were determined to select one protein/pH to produce the most stable emulsion for encapsulation. Overall, proteins (at pH 7.0) with high surface charge, low hydrophobicity and high solubility showed a better ability to lower interfacial tension, whereas proteins (at pH 3.0) with high surface charge, hydrophobicity, and better solubility can form stronger viscoelastic films at the interface. All proteins could form stable emulsions away from their isoelectric point. Therefore, the selection of an effective plant protein emulsifier for encapsulation entails finding a balance between the properties needed to associate at the oil-water interface with those needed to develop a strong interfacial film. As such, lentil protein isolate (LPI) at pH 3.0 was selected as the most promising emulsifier to produce a stable emulsion, due to its high surface charge, solubility, and hydrophobicity. In study two, the LPI-based wall materials (e.g., maltodextrin, sodium alginate, and lecithin) were used to encapsulate canola oil (as a model oil) using spray drying, in order to design a microcapsule formulation, which offered good physical properties (e.g., moisture content, water activity, color, wettability, particle size, surface oil, and entrapment efficiency) and oxidative stability. Initially, mixtures of LPI (2-8%, w/w in initial emulsions) and maltodextrin (9.5-18%, w/w in initial emulsions) were used to entrap canola oil (20-30%, w/w in final microcapsules). Emulsion (e.g., emulsion stability, droplet size, viscosity) and microcapsule (e.g., surface oil and entrapment efficiency) properties were then characterized to determine a better capsule design. The microcapsules prepared with 20% oil, 2% LPI, and 18% maltodextrin were selected as a baseline to re-design better microcapsules using different preparation conditions and wall materials (e.g., sodium alginate and lecithin). Overall, the combination of LPI (2%), maltodextrin (17%), and sodium alginate (1%) presented the best capsule design to offer the highest entrapment efficiency (~88%) and oxidative stability, because of the formation of an electrostatic complex between negatively charged sodium alginate and positively charged LPI. In study three, different omega fatty acid rich-oils (e.g., canola, fish, and flaxseed oils) were encapsulated by spray drying using the combination of LPI, sodium alginate, and maltodextrin. Physical properties, storage stability (e.g., free fatty acid content, peroxide value, 2-thiobarbituric acid reactive substances, and oxidative stability index) and in vitro release characteristics of encapsulated oils were investigated. Overall, all microcapsules displayed similar physical properties (except color). The combination of LPI, sodium alginate, and maltodextrin exhibited improved protection to susceptible oils from hydrolysis and oxidation in comparison with other microcapsules to entrap omega fatty acid-rich oils, and offered great antioxidative capacity, especially on fish oil, but oil-type had a significant effect on the rates of hydrolysis and oxidation. Minor amounts of encapsulated oils (~3.2-8.9%) were released under simulated gastric fluid, whereas the addition of simulated intestinal fluid resulted in significant oil release (~62.6-73.4%). In summary, LPI with good physicochemical and functional properties represented as a promising emulsifier to alternate soy and animal-derived proteins and to produce a stable oil-in-water emulsion for the development of microcapsules. The combination of LPI, sodium alginate, and maltodextrin can be potentially used as a universal platform to encapsulate more omega fatty acid-rich oils to fortify omega fatty acids in commercial food and supplements.
DegreeDoctor of Philosophy (Ph.D.)
DepartmentFood and Bioproduct Sciences
CommitteeLow, Nicholas; Green, Rick; Bandy, Brian; Tanaka, Takuji
Copyright DateFebruary 2017
Microencapsulation, omega fatty acid-rich oil, plant protein