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Coconut oil body membrane materials and storage proteins as emulsifiers : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand. EMBARGOED until 7 July 2027.
(Massey University, 2025) Şen, Aylin
As consumer preferences shift towards natural and sustainable food ingredients, plant emulsifiers are emerging as feasible alternatives to synthetic and animal-based options. This PhD thesis aimed to investigate the emulsifying potential of two coconut-derived components: oil body membrane materials (OBMMs) and press cake proteins. The study began with the extraction and characterisation of coconut oil bodies (OBs) from fresh and frozen coconuts (Chapter 4). The objective was to establish an extraction protocol that maximises the OB yield. The interactions between OB membranes and non-OB proteins were also examined through various washing techniques. Findings indicated that OB yield from frozen coconuts exhibited less variability than that from fresh coconuts and revealed considerable amounts of exogenous proteins within the OBM protein fraction. Next, the research focused on optimising the extraction and functionality of OBMMs obtained through churning or freeze–thawing (Chapter 5). The main goal was to identify OBMM composition and improve its emulsification properties via extraction method optimisation. Results showed that freeze–thawing proved more effective than churning for OBMM extraction yield, with an additional freeze–thawing step further improving the functionality of the resulting OBMMs. This project then investigated the extraction and fractionation of coconut oil press cake proteins with the goal of obtaining a fraction with emulsification properties (Chapter 6). Three protein fractions were produced for this purpose: those soluble at pH 7, soluble at pH 4.5, and insoluble at pH 4.5. Findings highlighted that variable costs, particularly raw material expenses, greatly impacted the production cost of pH 4.5 insoluble proteins. Finally, the emulsification properties of coconut press cake protein fractions (obtained in Chapter 6) were evaluated in oil-in-water emulsions (Chapter 7). Results show that pH 4.5 insoluble fraction exhibited the highest emulsification ability and emulsion stability. Additionally, the emulsions with excess proteins (> 1.5% w/w) showed a time-dependent flocculation, which was attributed the slow bridging interactions between adsorbed and unadsorbed proteins. Overall, this study characterises coconut-derived materials (OBMMs and press cake proteins) and determines their emulsifying capabilities to indicate their suitability for emulsion-based food systems. It also highlights that minimally purified plant materials can maintain functional properties, offering natural and sustainable emulsifier alternatives.
Biophysical insights into modulating lipid digestion in food emulsions
(Elsevier Ltd, 2022-01) Acevedo-Fani A; Singh H
During the last decade, major scientific advances on understanding the mechanisms of lipid digestion and metabolism have been made, with a view to addressing health issues (such as obesity) associated with overconsumption of lipid-rich and sucrose-rich foods. As lipids in common foods exist in the form of emulsions, the structuring of emulsions has been one the main strategies for controlling the rate of lipid digestion and absorption, at least from a colloid science viewpoint. Modulating the kinetics of lipid digestion and absorption offers interesting possibilities for developing foods that can provide control of postprandial lipaemia and control the release of lipophilic compounds. Food emulsions can be designed to achieve considerable differences in the kinetics of lipid digestion but most research has been applied to relatively simple model systems and in in vitro digestion models. Further research to translate this knowledge into more complex food systems and to validate the results in human studies is required. One promising approach to delay/control lipid digestion is to alter the stomach emptying rate of lipids, which is largely affected by interactions of emulsion droplets with the food matrices. Food matrices with different responses to the gastric environment and with different interactions between oil droplets and the food matrix can be designed to influence lipid digestion. This review focuses on key scientific advances made during the last decade on understanding the physicochemical and structural modifications of emulsified lipids, mainly from a biophysical science perspective. The review specifically explores different approaches by which the structure and stability of emulsions may be altered to achieve specific lipid digestion kinetics.
Formation of by high power ultrasound aggregated emulsions stabilised with milk protein concentrate (MPC70)
(Elsevier BV, 2021-12-03) Zhang R; Luo L; Yang Z; Ashokkumar M; Hemar Y
In this work, oil-in-water emulsions stabilised by milk protein concentrate (MPC70) were investigated. The MPC70 concentration was kept constant at 5% (close to the protein content found in skim milk) and the oil volume fraction was varied from 20 to 65%. Sonication was performed at 20 kHz and at a constant power of 14.4 W for a total emulsion volume of 10 mL. Under certain oil concentration (≥35%) and sonication times (≥3s) the emulsion aggregated and formed high-viscosity pseudo plastic materials. However, the viscosity behaviour of the emulsion made with 35% oil reverted to that of a liquid if sonicated for longer times (≥15 s). Confocal laser scanning microscopy showed clearly that the oil droplets are aggregated under the sonication conditions and oil concentrations indicated above. An attempt to explain this behaviour through a simple model based on the bridging of oil droplets by the MPC70 particles and, taking into account the oil droplet and MPC70 particle sizes as well as the oil volume fraction, was made. The model fails to describe in details the aggregation behaviour of these emulsions, likely due to the inhomogeneous protein layer, where both free caseins and casein micelles are adsorbed, and to the packing of the oil droplets at concentrations ≤55%. Nonetheless, this work demonstrates the potential of ultrasound processing for the formation of dairy emulsions with tailored textures.
Effect of Gel Structure on the In Vitro Gastrointestinal Digestion Behaviour of Whey Protein Emulsion Gels and the Bioaccessibility of Capsaicinoids
(MDPI (Basel, Switzerland), 2021-03-04) Luo N; Ye A; Wolber FM; Singh H; Kontominas MG
This study investigated the effect of gel structure on the digestion of heat-set whey protein emulsion gels containing capsaicinoids (CAP), including the bioaccessibility of CAP. Upon heat treatment at 90 °C, whey protein emulsion gels containing CAP (10 wt% whey protein isolate, 20 wt% soybean oil, 0.02 wt% CAP) with different structures and gel mechanical strengths were formed by varying ionic strength. The hard gel (i.e., oil droplet size d4,3 ~ 0.5 μm, 200 mM NaCl), with compact particulate gel structure, led to slower disintegration of the gel particles and slower hydrolysis of the whey proteins during gastric digestion compared with the soft gel (i.e., d4,3 ~ 0.5 μm, 10 mM NaCl). The oil droplets started to coalesce after 60 min of gastric digestion in the soft gel, whereas minor oil droplet coalescence was observed for the hard gel at the end of the gastric digestion. In general, during intestinal digestion, the gastric digesta from the hard gel was disintegrated more slowly than that from the soft gel. A power-law fit between the bioaccessibility of CAP (Y) and the extent of lipid digestion (X) was established: Y = 49.2 × (X - 305.3)0.104, with R2 = 0.84. A greater extent of lipid digestion would lead to greater release of CAP from the food matrix; also, more lipolytic products would be produced and would participate in micelle formation, which would help to solubilize the released CAP and therefore result in their higher bioaccessibility.
Emulsion-based delivery systems to improve gut and brain bioaccessibility of curcumin in relation to Alzheimer’s disease prevention : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
(Massey University, 2023) Lunelli, Taciana
Medium chain triglycerides (MCT) from coconut oil, omega-3 polyunsaturated fatty acids from fish, phospholipids from dairy milk, and curcumin from turmeric all have been recognized for their anti-inflammatory and antioxidant properties. Curcumin is also a potential candidate for Alzheimer’s disease (AD) prevention; however, curcumin is poorly bioavailable unless emulsified. The milk fat globule membrane (MFGM) has natural emulsifying properties. I aimed to design an emulsion-based delivery system containing functional oils to encapsulate and deliver curcumin to the brain. I evaluated three commercial MFGM components with coconut and fish oils to produce emulsions with improved curcumin bioavailability. The emulsion structures were characterised by particle size, zeta-potential at the surface, microscopic structure, curcumin loading efficiency, and phospholipid distribution. All emulsions showed stable to particle size changes over 40 days at 4°C. Emulsion particle size decreased significantly with increasing concentrations of emulsifier, and presented negative zeta-potential varying from -50 to -20 mV, with the MFGM fractions creating significantly different charges and curcumin loading efficiency based on phospholipid and protein composition. All MFGM fractions efficiently created stable emulsions with small particle size and encapsulated curcumin. After simulated in vitro digestion, the emulsion with the highest phospholipid content had significantly higher curcumin bioaccessibility compared to the others. Fresh and digested emulsions and their components were assessed in the BE(2)-M17 neuroblastoma cell model for amyloid-β (Aβ) toxicity. Emulsions composed of both fish and coconut oils provided greater protection against Aβ toxicity compared to coconut oil alone. Curcumin was transported in vivo across the intestinal wall to the bloodstream and across the blood-brain barrier to the brain in rats fed all curcumin delivery formats. The kinetics of curcumin in blood and brain varied depending on the emulsion format. MFGM emulsions significantly reduced the curcumin and its metabolites peak time in blood and brain compared to the commercial curcumin preparation Meriva®, and all emulsions improved overall curcumin bioavailability and accumulation in the brain compared to free curcumin. A novel ex vivo approach using rat plasma samples directly in the neuroblastoma cell model requires further optimisation but demonstrated a significant interaction between gender and treatment on cell viability.
Physico-chemical properties and stability of lipid droplet-stabilised emulsions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand
(Massey University, 2022) Cheng, Lirong
It is known that the structure of the interfacial layer impacts the stability and the function of emulsions. Hierarchical emulsions, known as droplet-stabilized emulsions (DSEs), were made from nano-sized primary oil droplets that coated with protein particles for potentially advanced functionality. In this study, the primary droplets were made of either rigid (whey protein microgel, WPM) or soft protein (Ca²⁺-cross-linked caseinate, Ca-CAS) particles. The structure of the protein particles and primary droplets in solution and at the oil-water interface were characterised; the oil exchange process between the surface and core oil droplets were examined, using light scattering, microscopy, small angle scattering, ultra-small angle scattering techniques, etc. The emulsification capacity of the primary emulsion has been shown to be improved by using soft and flexible protein particles, resulting in small droplet sizes and smooth interfacial layers of the DSE. The droplet-stabilised interfacial layer has been shown to provide DSE a good stability against coalescence during gastric enzymatic hydrolysis, long-term storage, and heating, as well as improved functionalities in the rate of the lipolysis during simulated intestinal digestion and the rheological properties at high oil content. Overall, this research provided new information on DSE physical-chemical properties and stability as affected by the structure of emulsifiers (protein particles and the subsequent primary droplets), digestion destabilisation, pH, storage time and temperature. The outcomes have potential for designing functional foods with improved active compound delivery and mechanical strength.
Structured emulsion gel systems for delivery of bioactive compounds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand
(Massey University, 2021) Luo, Nan
The structure of solid/semi-solid foods greatly impacts on how the food is broken down and digested in the human body, which affects its sensory perception, and the bioaccessibility of nutrients. In this project, heat-set whey protein emulsion gel was used as a model system for solid/semi-solid foods for the delivery of capsaicinoids (CAP); the capsaicinoids were dissolved in the emulsion droplets. The aim was to investigate the effect of emulsion gel structure on the breakdown properties and sensory perception of the gel in human mouth and to understand how gel structure affects its digestion behaviour as well as the release of capsaicinoids during in vitro gastrointestinal digestion. Small and large deformation properties as well as the microstructure of the emulsion gel were evaluated. Eighteen human subjects were used to investigate in vivo oral processing behaviour and sensory perception. The Human Gastric Simulator (HGS) was used for in vitro dynamic gastric digestion and pH-stat for simulated intestinal digestion. Human intestinal epithelial cells Caco-2 were used to evaluate the irritation effect of gastric digesta by the quantification of human interleukin-8 (IL-8) production using enzyme-linked immunosorbent assay (Elisa). Based on the rheological properties, the gels were classified into three groups: semi-solid gel (whey proteins as emulsifier, 10 mM NaCl with d4,3 of ~ 0.2 µm); soft and elastic gels (whey proteins as emulsifier, 10 mM NaCl with d4,3 of ~ 4, 1 and 0.5 µm); hard and brittle gels (whey proteins as emulsifier, 100 mM NaCl with d4,3 of ~ 4, 1, 0.5 and 0.2 µm). Results from in vivo study indicated that the degree of gel fragmentation during mastication was positively correlated with gel hardness (represented by Young’s modulus). A higher degree of fragmentation led to a greater surface exposure during mastication and, therefore, a greater release of capsaicinoid molecules, resulting in greater mouth burn perception. Results from in vitro gastrointestinal digestion of CAP-loaded soft gel and CAP-loaded hard gel showed that the hard gel was disintegrated and hydrolysed slower than the soft gel during gastric digestion. The rate and extent of lipid digestion during intestinal digestion were affected by several factors, such as fat content, gel structure, gel particle size and initial oil droplet size of the gastric digesta. Generally, the soft gel had higher degree of lipid digestion, mainly because of its soft gel structure and lower fat content. The bioaccessibility of CAP was found to be positively correlated with the extent of lipid digestion. The effect of active (whey proteins as emulsifier) versus inactive (Tween 80 as emulsifier) filler particles of CAP-loaded emulsion gels was also investigated. CAP-loaded Tween-80-coated oil droplets were not bound within the whey protein matrix (i.e. emulsion gels containing inactive filler particles) and appeared to be flocculated and heterogeneously distributed in the gel matrix; this led to drastically decreased gel strength. On the other hand, the whey-protein-coated oil droplets had strong interactions with surrounding whey protein matrix contributing to gel strength, and the oil droplets were relatively evenly distributed in gel matrix in CAP-loaded whey protein emulsion gels (i.e. emulsion gels containing active filler particles). During in vivo oral processing, CAP-loaded Tween 80 emulsion gels were readily broken down into small fragments in the mouth at small deformations with less chewing and released large amounts of oil droplets from the gel matrix. In general, the mouth burn perception was positively correlated with degree of gel fragmentation. The large amounts of oil droplets released from the gel matrix during mastication and the inhomogeneous distribution of the oil droplets of the CAP-loaded Tween 80 emulsion gels also contributed to their greater mouth burn perception. During in vitro gastric digestion, the gel with inactive filler particles was disintegrated and emptied out faster than gel with active filler particles, due to its significantly smaller masticated particle size entering the stomach. Large amounts of oil droplets were released during gastric digestion from the gel with inactive filler particles while gel with active filler particles had minor release of oil droplets at the end of digestion. During intestinal digestion, the presence of Tween 80 in gel with inactive filler particles has slowed down the rate and extent of lipolysis, because Tween 80 had certain resistance against replacement by bile salts from the interface. Moreover, the Tween 80 molecules, once displaced by bile salts from the interface, would also participate in the formation of mixed micelles and help solubilize the released CAP molecules, therefore, leading to improved bioaccessibility of CAP. An in vitro method was developed to quantify the gastric irritation of CAP-loaded food formulations during gastric digestion. Results suggest that Caco-2 cells had immune responses to CAP-loaded samples by secreting significant amounts of IL-8, confirming that CAP molecules are inflammatory to Caco-2 cells. The emulsion gel structure was modified using different emulsifiers: whey proteins versus Tween 80. The gastric digesta from CAP-loaded Tween 80 emulsion gel was able to stimulate more IL-8 production than CAP-loaded whey protein emulsion gel. Tween 80 was found to be a proinflammatory factor to Caco-2 cells and could stimulate IL-8 secretion. Overall, this research provided new information on the use of solid/semi-solid systems for delivery of capsaicinoids and how food structure affects disintegration and digestion behaviour and eventually the release of capsacinoids. The outcomes have potential for designing functional foods containing capsaicinoids, with increased incorporation of capsaicinoids in the foods / pharmaceuticals, reduced irritation in the mouth and stomach and increased bioaccessibility in the intestine.
Carbohydrate-based oil-in-water emulsions for delivery of short-chain fatty acids : Doctor of Philosophy in Food Technology at Riddet Institute, Massey University, Palmerston North, New Zealand
(Massey University, 2021) Le, Hoang Du
Short-chain fatty acids (SCFAs) are important functional metabolites. There is clinical evidence to show that they are useful in the prevention of the metabolic syndrome, bowel disorders and certain types of cancer. Therefore, supplementation of SCFAs to the daily diet brings benefits to human health. However, SCFAs are small and water-soluble molecules that are quickly absorbed in the upper gastrointestinal tract. This project aimed to develop carbohydrate-based systems to deliver tripropionin (TP, glycerol tripropionate) and tributyrin (TB, glycerol tributyrate) as sources of propionic and butyric acids into the colon. Two types of emulsion systems were employed, i.e. surfactant-stabilised oil-in-water (O/W) emulsions (single and double-layer systems) and particle-stabilised O/W emulsions (Pickering emulsions). The systems were characterised in terms of structural stability, surface charge, rheological properties, lipolysis degree and release of SCFAs under a static in vitro gastrointestinal digestion and an in vivo study with ileal-cannulated pigs. In the screening experiments, several potential carbohydrate materials were explored, i.e. three modified starches (GUM, N46 and N-LOK), four pectins (PEC) and hydrophobically modified inulin (M-IN), to produce single-layer O/W emulsions. A double-layer O/W emulsion was also produced by combining whey protein isolate (WPI) and chitosan (CS) as the first and second layers, respectively. The capacity of emulsion systems for colon-targeted delivery of SCFAs was then tested using a static in vitro gastrointestinal digestion. The results show that PEC displayed the poorest emulsifying capacity amongst all investigated carbohydrates, leading to an emulsion droplets size (d32) of around 7.3 µm. However, PEC-based formulation was the best system for protection against gastric and intestinal conditions. On the other hand, other single-layer systems and the double-layer system proved to be unstable in the intestinal phase with a significant SCFA release. Deeper investigation on the emulsifying capacity showed that PEC stabilised the O/W emulsion mainly through steric effects. In addition, PEC had the ability to form thick layer around the O/W interface, which was evidenced by confocal laser scanning microscopy and the quantification of adsorbed PEC on the interface. In addition to the above systems, a Pickering O/W emulsion stabilised by hydrophobically modified cellulose nanocrystals (CNCs) was also investigated. The hydrophobic modification of CNCs was carried out, resulting in an increase in static water contact angle from 56o (untreated CNCs) to 80.2o (MCNCs). As a result, the emulsifying capacity of MCNCs was significantly improved. The emulsions prepared from MCNCs ≥ 0.20 wt% were stable against droplet coalescence for up to 4-week storage. In addition, the Pickering emulsions were prone to droplet flocculation at ionic strength ≥ 20 mM NaCl (pH 7.0) or pH < 4.0 (without addition of NaCl), which was due to the charge screening associated with the cellulose molecules at the surface. Similar droplet flocculation was also observed under in vitro gastric conditions, where the emulsions were exposed to low pH and high ionic strength. This gastric-induced structural changes improved physical strength of the emulsions and that enhanced resistance to bile-salt displacement and consequently delayed lipid digestion in the intestinal conditions. In addition, high desorption energy of the MCNC particles at O/W interface of the Pickering emulsion contributed to low lipolysis degree (30–35%). High proportions of SCFAs remaining after the intestinal digestion observed in both PEC and MCNC-based emulsions show a strong promise their use in the colon-targeted delivery of SCFAs. However, CNCs are currently not considered as food-grade materials; therefore, PEC was chosen for the in vivo study using female ileal-cannulated pigs. The in vivo study demonstrated significant higher intestinal lipolysis (~ 51–53%) and lower SCFA release (~ 15%) as compared to the in vitro digestion (~ 40 and 35% respectively). The main reason for the difference between the two models was the absorption of the SCFAs in the pig’s small intestine. However, high proportions of unhydrolysed triglycerides (~ 47–49%) and presence of oil droplets in the ileal-digesta demonstrated successful delivery of SCFAs. Based on the findings in this research, we propose the use of PEC-based emulsion for human trials by incorporating the system into a daily diet or dessert liquid/gel products, such as drinking milk or yogurt. We also believe that the application of MCNC-based Pickering emulsions for colon-target delivery of could be of interest if the regulatory status could be confirmed. The study identifies promising directions for researchers who are interested in improving gut health through delivery of SCFAs to the colon.
Development of microemulsion delivery systems for bioactive compounds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Auckland, New Zealand
(Massey University, 2020) Yuan, Quan
Many bioactive compounds for health benefits are not readily stable against degradation and their solubility is also very low. As a result, a delivery system is required to encapsulate and protect bioactive compounds for their food applications. Emulsion is one of the delivery systems which has been studied by many researchers. But emulsion tends to destabilize during storage and its opaque optical properties makes it difficult for its use and incorporation into clear foods or beverages without affecting their original appearance. Therefore, microemulsion, which is known to be transparent, has been investigated to some extent to encapsulate and deliver bioactive compounds as a potential delivery system. The objective of this research was to fabricate oil-in-water (O/W) microemulsions which might be utilised as the delivery system for bioactive compounds. This thesis is mainly composed of two sections. The first section was to produce microemulsions via emulsion dilution method and water titration method as well as to study the characteristics of these microemulsions. Beta-carotene was a type of bioactive compound used in the second section to study the effect of beta-carotene on the formation and properties of microemulsion which was fabricated using the same methods described above. At first, emulsion dilution method was employed to fabricate microemulsions with different types and concentrations of oils, such as peanut oil, fractionated coconut oil, isopropyl myristate (IPM), lemon oil and Capmul 708G, and also with different surfactants (Tween 20, 40, 60 and 80). It was found that peanut oil and fractionated coconut oil could not be utilised to form microemulsions by this method, whereas IPM and lemon oil had the ability to fabricate microemulsions. When 1% Tween 80 was introduced as the surfactant and dilution medium, microemulsion could be formed when the concentration of IPM was less than 0.1% and that of lemon oil was less than 0.2%. Among the different types of Tween surfactants, Tween 80 was the most efficient when its solution containing Tween micelles was used as a dilution medium compared to the other Tween surfactants because more lemon oil could be incorporated into the Tween 80 micelles with an increase in Tween 80 concentration. In the following study, a water titration method was employed to create ternary or pseudo phase diagrams which indicated the ability to fabricate microemulsions of a mixture system. Various types of oils (Captex 100, Capmul PG-8, Capmul PG-12, Capmul PG-2L, lemon oil, Capmul MCM C8, Capmul 708G and Captex 355) and surfactants (Tween 80, Tween 20, Span 80 and Kolliphor EL) were used in this study. Absolute ethanol and propylene glycol (PG) were also incorporated as cosurfactant and cosolvent, respectively. It is concluded that all these oils and surfactants could be utilised by the water titration method to produce microemulsions, however, their ability to form microemulsions were different. Capmul 708G, which is a monoglyceride, was the most efficient in terms of producing microemulsions compared to diglyceride and triglyceride. Tween 20 and Kolliphor had the similar emulsifying properties compared to Tween 80 whereas Span 80 was not efficient. Both absolute ethanol and PG could assist the formation of microemulsions when they were introduced into the mixture system of oil, surfactant and water. In the following study, microemulsions containing 0.1% and 0.4% lemon oil and an emulsion containing 1.5% lemon oil (larger oil droplets), which were fabricated by the emulsion dilution method, were chosen to incorporate beta-carotene as a lipophilic model bioactive compound into lemon oil in order to study its impact on the formation and properties of the resulting microemulsion and emulsion systems. The encapsulation of beta-carotene into 0.1% and 0.4% lemon oil caused a significant increase in the particle size of the O/W microemulsions, but the particle size was still within the size range of microemulsion. As a result, the beta-carotene-loaded microemulsions containing 0.1 and 0.4% lemon oil were visually clear in appearance. However, the incorporation of beta-carotene did not increase and alter the particle size of the emulsion containing 1.5% lemon oil. The microemulsion sample containing 0.1% lemon oil and the emulsion containing 1.5% lemon oil were stored at 25 °C without exposed to oxygen and light for one month. While, the microemulsion containing 0.4% lemon oil was selected and placed at three different temperatures (4, 25 and 37 °C) for 1 month: at 4 and 37 °C without exposure to both oxygen and light and at 25 °C, four different environmental conditions (i.e. with oxygen/light, with oxygen and without light, without oxygen and with light, without oxygen/light). The results showed that the rate of beta-carotene degradation was lower in all these three samples when compared to the beta-carotene present in a hexane solution without encapsulation. Higher temperature accelerated the degradation rate of beta-carotene. As a consequence, the 0.4% lemon oil microemulsion at 4 °C exhibited the slowest degradation rate of beta-carotene. Next, the microemulsions fabricated by the water titration method were selected to encapsulate beta-carotene to study the encapsulation capacity of these microemulsion systems as well as their ability to protect beta-carotene against oxidative degradation during storage. Capmul 708G, Tween 80, Milli-Q water and PG mixture system were chosen to fabricate microemulsions and two formulations (L910 and L990) were prepared to incorporate beta-carotene. L910 was comprised of 81% Capmul 708G, 9% Tween 80, 5% water and 5% PG, whereas L990 contained 9% Capmul 708G, 1% Tween 80, 45% water and 45% PG. It was able to see clearly from this experiment that the L910 system could incorporate more beta-carotene than L990. Both L910 and L990 could reduce the degradation rate of beta-carotene when loaded into them compared to their presence in hexane solutions without encapsulation. Similar to the previous experiment as described above, when the beta-carotene incorporated microemulsions were placed at 4 °C and away from oxygen and light, beta-carotene had the highest retention rate after storage for 1 month. Furthermore, beta-carotene degradation rate in L910 was slower than that in L990, indicating L910 was more effective than L990 in terms of incorporating and protecting beta-carotene. It is shown clearly from the present study that microemulsions could be formed via the water titration and emulsion dilution methods. The type and concentration of oil phase and surfactant had a significant influence on the determination of whether a mixture system could form a microemulsion as well as the properties of the formed microemulsion. The microemulsions produced by these two different methods could be utilised to encapsulate beta-carotene as the incorporation of beta-carotene did not have a significant influence on the properties of the original microemulsions. Moreover, microemulsions provided the stability and protection to beta-carotene against oxidative degradation that could be caused by oxygen, light and temperature during storage, which might be possible to be applied to some liquid foods and beverages.
Studies on formation, oxidative stability and plausible applications of food-grade 'droplet-stabilised' oil-in-water emulsions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Riddet Institute, Massey University, Palmerston North, New Zealand
(Massey University, 2019) Okubanjo, Samantha Sewuese
This research was aimed at studying the structural characteristics, chemical stability and plausible functional applications of droplet-stabilised oil-in-water emulsions (DSEs). DSEs consist of oil-in-water droplets (the core) stabilised by submicron protein-stabilised oil droplets (the shell). The first objective was to increase our understanding of their structural properties and processing factors that contribute to DSE formation using food grade ingredients. To achieve this objective, milk protein concentrate (MPC) was chosen as the emulsifier. Four MPCs with different levels of calcium were used. The surface lipid (20 %) consisted of either a low (olive oil), medium (palmolein oil) or high (trimyristin) melting surface lipid. The core lipid (20 %) consisted of either a triglyceride (soybean oil) or pure fatty acid (linoleic acid). Protein-stabilised shell emulsions were processed either via the microfluidizer (170 MPa) or two-stage homogeniser (1st stage-20 MPa; 2nd stage-4 MPa). Results of the study showed that aggregated structure of protein emulsifier, shell droplet concentration, surface and core lipid types influenced the formation and structural properties of DSEs. The second objective focused on investigating the chemical stability of DSEs by evaluating their stability to oxidation and ability of its interfacial structure to protect polyunsaturated lipids incorporated within from oxidation. To achieve this objective, oxidative stability of high linoleic acid oil (safflower oil) stabilised by protein-coated low (olive oil), medium (palmolein oil) and high (trimyristin) melting lipid droplets was evaluated and compared with composition-matched conventional protein-stabilised safflower oil-in-water emulsion as well as a conventional protein-stabilised safflower oil-in-water emulsion (reference emulsions). Influence of physical state of high melting lipid droplets on oxidative stability of droplet-stabilised safflower oil emulsion was also evaluated. High linoleic acid (72.54% of total fatty acids) safflower oil (20%) was used because of its high susceptibility to oxidation. Olive oil (low acidity), palmolein oil and trimyristin were chosen because of their low susceptibility to oxidation. The study showed that safflower oil oxidation in DSEs was reduced by about 40-55% in comparison to conventional emulsions. High melting surface lipid DSEs provided better protection for safflower oil than low and medium melting surface lipid DSEs. The third objective aimed at improving our understanding of the influence of antioxidant’s location in emulsions on antioxidant performance. The study was also focused on exploring a plausible functional application of DSEs by incorporating a hydrophobic antioxidant in shell droplets (at the interface) of DSEs rather than in the interior of the core unsaturated lipid. To achieve this objective, butylated hydroxyanisole (BHA) a common commercially used synthetic hydrophobic antioxidant was chosen. BHA was incorporated either in shell droplets or core droplets of DSEs. The ability of BHA to counteract oxidation when incorporated in low (olive oil) and high melting (trimyristin) shell droplets of DSEs was evaluated and compared with BHA’s anti-oxidation performance when incorporated directly in core droplets (safflower oil) stabilised by low (olive oil) and high melting (trimyristin) shell droplets without BHA. Results of the study indicate that ability of BHA-in-shell DSEs to counteract oxidation of core safflower oil better than BHA-in-core DSEs is influenced by BHA’s concentration and transfer mechanism to reaction sites. The fourth and final objective was aimed at investigating mobility of a hydrophobic antioxidant incorporated at the interface of DSEs to establish their location after emulsification. The study focused on determining if a hydrophobic antioxidant incorporated in shell droplets remained localised within or migrated overtime to core droplets. The study also investigated the use of two techniques (saturated transfer difference (STD)-nuclear magnetic resonance and confocal Raman microscopy) to determine partitioning of antioxidants in DSE. To achieve this objective, confocal Raman spectroscopy technique was employed to probe antioxidant location without phase separation or destruction of DSE structure. Beta-carotene was chosen for the study for its excellent Raman scattering property. Beta-carotene was incorporated either in shell droplets (olive oil and trimyristin) or core droplets (safflower oil) of DSEs. Location and mobility of beta-carotene was evaluated after three days production. Beta-carotene migration from low (olive) and high melting shell droplets to core safflower oil was minimal. The present study provides processing conditions and structural characteristics required to form food-grade DSEs. The study confirms and establishes the potential of DSEs to effectively protect oxidation-sensitive lipophilic bioactives incorporated within from degradation and confirms the viability of concurrent incorporation of two different bioactives in DSEs emulsions by locating one bioactive in shell droplets and the second within the core.

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