Designing Delivery Systems Of Vitamin E To Enhance Its Stability And Bioaccessibility

There are a number of challenges that must be overcome before Vitamin E (VE) can be successfully incorporated into commercial foods due to its low water-solubility, poor chemical stability and variable bioaccessibility. Many of the challenges associated with using VE can be overcome by incorporating it into delivery systems that can be dispersed into food and beverage products. Although nanoemulsions (droplet diameter:20-200 nm) have got great potential for the delivery of VE, they are found to be prone to droplet aggregation against physicochemical stresses including unfavorable pH, high salt concentrations, thermal processing temperatures and excessive exposure to light. Moreover, the food industry would like to prepare nanoemulsions from commonly used and acceptable food grade ingredients (such as flavor oils, triglyceride oils, proteins and polysaccharides). Therefore, this work focused on formulation and successful encapsulation of VE using food biopolymers:Octenyl Succinic Anhydride (OSA) modified starches (MSs). High energy and low energy emulsification methods were used to encapsulate VE. The degradation kinetics, thermal and storage stability of VE nanoemulsions and VE nanocapsules obtained by spray drying technique and in vitro VE bioaccessibility were studied.Initially, to study the formation and stability of VE based nanoemulsions; high-energy emulsification method (High pressure homogenization) was used to design VE delivery systems. Influences of interfacial tension, VE viscosity, molecular weight distribution and surfactant type (MSs versus Tween 80) on stability and droplets’size were investigated. Results showed that MSs with high-dispersed molecular density (p) and Radius of Gyration (Rz) formed micelles with compact and larger dimensions, hence resulting in high critical micelles concentration (CMC). Both surfactants reduced interfacial tension and small droplet diameters (<350 nm) were produced at high VE content (80% oil phase, w/w) and low emulsifier (2.5%, w/w), which was attributed to their molecular distribution and interfacial characteristics and the magnitude of disruptive forces generated within homogenizer. MSs stabilized nanoemulsions were stable to droplet coalescence at high temperature short time exposure (30,55,80℃; 30 min). Results indicated that using High-Pressure homogenization, MSs could be used successfully to stabilize VE nanoemulsions at ambient temperatures.To gain more insights into the physicochemical stability and thermal degradation, VE nanoemulsions were also produced using low energy emulsification method known as Emulsion Phase Inversion (EPI) with different carrier oils (short-chain, medium-chain and long-chain triglycerides) and Tween 80. Although nanoemulsions made with VE and the 3 carrier oils showed physical stability to heat shock (30-90℃,30 min), ionic strength (0-500 mM), pH (2.0-8.5) and long term storage (60 days, under light and darkness,4,25 & 40 ℃), there was significant VE degradation in heat processed and long-term storage samples. The VE degradation in long-term storage fitted well with Weibull model, while heat degradation followed the first order kinetics, with medium-chain triglyceride (MCT) based nanoemulsions held at 90℃ showing the greatest degradation rate (k=0.1526×10-3/min) and lowest half-life of 4.54 min. The lack of droplets aggregation or coalescence was associated with absence of electrostatic screening and ion-binding effects. The nanoemulsions stored at 4℃ were more stable than those at 40℃. The short-chain triglyceride (SCT) based nanoemulsions did not physically withstand the high temperatures (>25℃) while long-chain triglyceride (LCT) showed good retention in all studied conditions. The VE retention was increased when nanoemulsions were stored in the dark.The comparison between low- and high-energy emulsification methods showed no appreciable difference in the behaviour of nanoemulsions produced using both methods in terms of their physical stability when they had similar initial compositions though the droplets produced by high-energy method were slightly larger than others. On the other hand, OSA modified starches were unable to form nanoemulsions using low energy emulsification method.To overcome those limitations associated with the aqueous delivery systems, spray-drying technique was used to fabricate VE loaded nanocapsules using MSs as emulsifiers and wall materials. Several physicochemical properties of MSs that are expected to influence emulsification capacity, retention and storage stability of VE in nanocapsules were investigated. High Degree of Substitution (DS), low Molecular Weight (Mw) and low interfacial tension improved emulsification properties while Oxygen Permeability (OP) and Water Vapor Permeability (WVP) affected the film forming properties. The degradation profile of Vitamin E fitted well with the Weibull model. Nanocapsules from MS-A and MS-B retained around 50% of VE after a period of 60 days at 4-35℃. Reduced retention and short half-life (35 days) in nanocapsules fabricated using MS-C at 35℃ were attributed to autoxidation reaction occurred due to poor film forming capacity. These results indicated that low molecular weights OSA modified starches were effective at forming stable VE nanocapsules that could be used in drug and beverage applications.Since some of the physicochemical properties of MSs were found to affect VE retention and storage stability in nanocapsules, further investigation was necessary to evaluate their effect on VE bioaccessibility. Therefore, in vitro model consisting of simulated mouth, stomach and small intestine was developed to access the influence of physicochemical properties, in vitro digestibility and molecular characteristics of MSs on VE bioaccessibility. It was revealed that MS-B with small droplet diameter yielded more FFAs while MS-C, which contained the highest Resistant Starch (RS) (19.14%) was less susceptible to the digestive lipase. Low molecular weight (Mw) and p increased the micellization of VE by forming less branched and less dense structures around the oil phase that was easily displaced by the bile salts and phospholipids in GIT. Results on in vitro FFA release and bioaccessibility were in agreement with those on the decrease in RS. The contents in rapid digestible starches (RDS), slowly digestible starches (SDS) and RS were found to be the main factors determining the extent of nutraceutical release during in vitro digestion when modified starches were used as stabilizers.