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Item 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 SewueseThis 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.Item The oxidation stability of extra virgin avocado oil : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Science at Massey University(Massey University, 2002) Sherpa, NimmaExtra virgin avocado oil (EVAO) is extracted from avocado fruit with minimal processing. It contains a wide range of non-lipid compounds that have a profound affect on oil stability. The deterioration of oil quality is due to autoxidation and photooxidation reactions that occur during oil storage. The objectives of this research were to determine the effect of prooxidant factors (light, temperature, oxygen level) on oil oxidation and quality; make recommendations for oil processing and packaging procedures to minimise oxidation; predict the shelf life of the oil and to determine the effect of commercial antioxidants on oil oxidation. An accelerated oxidation reactor was developed to test the effects of fluorescent light, elevated temperature and varying oxygen levels on the peroxide value (PV) (initially 0.96 ± 0.03 meq/kg oil) and chlorophyll content (initially 16.2 ± 0.1 ppm) of EVAO. The production and packaging processes of Olivado NZ. were analysed for exposure to oxidation promoting factors. EVAO was exposed to dark storage at 50°C and 60°C in order to determine Q10 values for oil oxidation. Several commercial antioxidants were evaluated by examining their affect on EVAO using the Rancimat oil stability index analysis and hot air oven testing. It was found that fluorescent light at 4500 lux and aeration with dry air strongly accelerated the oxidation (determined by PV) and reduced the chlorophyll content of EVAO. The average effect of 4500 lux fluorescent light compared to 0 lux over seven hours was a PV increase of 4.5 ± 1.4 meq/kg oil and decrease in chlorophyll content by 0.9 ± 0.3 ppm. The average effect of aerated EVAO compared to EVAO stored at ambient oxygen levels over seven hours was a PV increase of 3.5 ± 1.7 meq/kg oil and a chlorophyll content decrease of 0.3 ± 0.2 ppm. Exposure to an elevated temperature of 60°C for seven hours did not cause a significant increase in PV. Recommendations were made to minimise the exposure of the oil to light, aeration, water and fruit sediment during production and packaging in order to minimise oxidation of the oil. Due to the breakdown of natural antioxidants and alternative side reactions that occurred at elevated test temperatures but not at ambient temperatures, the shelf life of the oil could not be defined. EVAO containing ascorbyl palmitate at a level of 100 ppm had a peroxide value 80 % less than control EVAO with no antioxidants after 500 hours storage at 60°C. Ascorbyl palmitate has GRAS status and was concluded to be the most effective antioxidant of those tested in EVAO.Item Shelf life of goat infant formula powder : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Chemical and Bioprocess Engineering at Massey University, Palmerston North, New Zealand(Massey University, 2015) Lai, Po-HanOxidative rancidity was found to be a problem in goat milk infant formula powder. Oxidative rancidity results from the lipid oxidation processes, where oxygen reacts with unsaturated fatty acids from milk powder to produce lipid hydroperoxides and radicals, the primary oxidation products. These primary oxidation products are odourless; however, they are very reactive to breakdown into hydrocarbons, aldehydes and ketones. Aldehydes have low flavour threshold limits and are responsible for causing the rancid flavour in the milk powder. Peroxide value (PV) is one of the most widely used tests for oxidative rancidity as it is a measure of the concentration of lipid hydroperoxides; however, it is difficult to provide a specific guideline relating PV to rancidity. A reliable test is needed to determine whether the goat milk infant formula powder is unacceptable due to oxidative rancidity to the consumer. It was found that oxygen was a useful parameter to monitor lipid oxidation. Oxygen is the main reactant in lipid oxidation, and the rate of oxygen consumption is a useful tool to track lipid oxidation. Hexanal was determined to be the main secondary oxidation product responsible for the off flavour of milk powder. An experiment of accelerated storage trials for two infant formula products (Powder A and Powder B) was conducted by using a range of higher temperatures from 37°C to 57°C over a period of 12 to 24 weeks. Headspace oxygen and headspace hexanal of the milk powder in the glass vials were measured over the storage period. Sensory analysis was also conducted in parallel with the storage trial to provide a relationship between the sensory score and hexanal concentration, ultimately determining the unacceptable flavour threshold limit for hexanal concentration. The chemical kinetic constants were estimated by fitting a general nth order reaction with an Arrhenius law model with the concentration of oxygen obtained experimentally. The model followed half order reaction for both products. The Arrhenius rate constant, k0, and activation energy, E, were found to be 7.8×109 % 0.5 week-1 and 62.0 kJ mol-1 for Powder A and 1.34×107 % 0.5 week-1 and 45.60 kJ mol-1 for Powder B. It was discovered that oxygen and hexanal were highly correlated with R2 of 0.905 for Powder A and R2 of 0.918 for Powder B when fitted exponentially. It was predicted that Powder A would be unacceptable after a storage time of 40 weeks, and 31 weeks for Powder B under 25°C storage temperature. Data tables were generated to outline the different maximum storage times allowed with different storage temperatures and different initial storage oxygen concentration.Item Advanced platform for shelf life extension in liquid foods : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Bioprocess Engineering at Massey University, Palmerston North, New Zealand(Massey University, 2012) Brown, ColinThe shelf life of lipid based foods is often determined by the development of rancid flavours attributed to lipid oxidation reactions. These reactions are highly complicated and readily change when the reaction system is altered. As a result, researchers have struggled to make significant advances in their understanding of the mechanisms and rates of lipid oxidation. This thesis focuses on the generalised three step mechanism of lipid oxidation and develops understanding, through mathematical modelling exercises, about the factors that influence the rates of lipid oxidation. More specifically, this thesis focuses on bulk oils, bulk oils with added antioxidants, oil-in-water emulsions and the effects of oxygen supply and consumption rates in real food systems. For this thesis, methods were developed to identify and validate findings that suggest that lipid hydroperoxides are the rate defining reactant in lipid oxidation reactions. These methods were then used to measure the solubility of oxygen in oil and to define the role oxygen plays in determining the rates of lipid oxidation in a range of systems. The use of a newly developed batch oxidation apparatus led to the development and validation of models to predict the rates of oxygen consumption during oxidation. The model showed that the rates of oxygen consumption were half order with respect to the lipid hydroperoxide concentration. Through further validation experiments, it was shown that, during the initial stages of lipid oxidation before rancidity, each mole of lipid hydroperoxides formed required 5.04 moles of oxygen to be consumed when there was oxygen present. The same model and methods were then used to predict the changes in rates of lipid oxidation triggered by changes in reaction temperature. From this work, it was found that the Arrhenius law was capable of predicting the rates of oxygen consumption. The addition of butylated hydroxyanisole (BHA) to mixed fish oil samples brought with it a reduction in the rates of lipid oxidation, the magnitude of which was proportional to the concentration of BHA added. It was found that the inclusion of a modifier into the half order model was capable of predicting the rates of lipid oxidation when antioxidants were added. Methods to quantify the modifier were supplied for future use. The dilution of bulk oils by the formation of oil-in-water emulsions was also studied. It was found that the rates of lipid oxidation were proportional to the concentration of lipids in the emulsion. It was shown that the extent of oxidation during a batch oxidation was inversely proportional to the concentration of lipids in the emulsions as the aqueous phase acted as sump of oxygen for reaction in the oil droplets. Through modelling and short validation exercises, it was shown that changes to the surface area to volume ratio of oil droplets in emulsions had no effect on the rates of oxygen supply/lipid oxidation and that any effects noted in literature are likely to be the result of other surface active compounds. Finally, a modelling exercise showed that the rates of oxygen consumption via reaction were likely to be significantly faster than the rates of oxygen supply in unmixed systems in polymer packaging and, to some extent, open to the atmosphere. The diffusion of lipid hydroperoxides was shown to be important in bulk oils stored in polymer packaging as it allowed for a greater proportion of the oil to react with the oxygen transferred, thus reducing the potential for the oxygen supplied to take part in secondary and tertiary product formation. It was suggested that it is better, for a given quantity of oxygen supplied, for the entire oil product to react as it would result in fewer tertiary products being formed than if the oxygen were to be consumed at the surface of the oil only. Following this, it was suggested that an oil-in-water emulsion should be less stable than a bulk oil. Short experimental work showed that storing bulk oils in the absence of oxygen brings with it a decrease in the rates of lipid oxidation caused by a decrease in the concentration of lipid hydroperoxides. This decrease, coupled with anecdotal evidence that products do become rancid over long periods of time, suggests that the radicals formed during lipid hydroperoxide breakdown can be used in two different sets of reactions. That is, the relative rates of reformation of lipid hydroperoxide via reaction with lipids and the formation of tertiary oxidation products will likely determine the rates of lipid hydroperoxide breakdown and rancidity in real food systems. An indepth analysis of lipid hydroperoxide breakdown rates in the absence of oxygen as well as a set of validation experiments for the storage of bulk oils and oil-in-water emulsions in polymer films was suggested as being the final piece of information needed to complete a comprehensive model capable of quantitatively predicting the rates of lipid oxidation reactions and the shelf life of lipid oxidation prone foods.Item The electrochemical oxidation of hydrogen peroxide on platinum electrodes at phosphate buffer solutions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Palmerston North, New Zealand(Massey University, 1999) Khudaish, Emad AldeenThe kinetics and mechanism for the electrochemical oxidation of H2O2 on platinum electrodes in phosphate buffers were studied. A mechanistic model for this reaction was developed that involves binding sites, on the surface of the electrode, that are thought to be based on some form of hydrous platinum oxide, initially identified as Pt(OH)2. Hydrogen peroxide adsorbs onto the binding sites to form the complex Pt(OH)2·H2O2. The complex then undergoes internal electron transfer to form a reduced platinum site, Pt, with the release of the products water and oxygen. The binding sites regenerate electrochemically to give rise to an amperometric signal together with the release of protons. Two side reactions were proposed, the first involved a competitive inhibition of the binding sites by oxygen to form the species Pt(OH)2·O2. The second involved a non-competitive inhibition of the complex Pt(OH)2·H2O2 by protons. A rate equation was derived to account for all electrode sites involved in the proposed mechanism, with kinetic parameters for electrode reactions, and was validated over a range of bulk [H2O2], rotation rates, potentials, temperatures, buffer concentrations and pH. The kinetic and equilibrium constants for the model were optimised using a SIMPLEX procedure. The equilibrium constants were found to be potential- and temperature-invariant (K1 = 6.38 x 10-3 m3 mol-1, K4 = 0.128 m3 mol-1 and K5 = 0.053 m3 mol-1). The diffusion coefficient for H2O2 was found to be in the range 0.55 - 0.66 x 10-9 m2 s-1. These values were lower than those reported in the literature. The rate constants, k2N and k3N, were found to vary with potential and temperature, and pseudo-activation energies for k2 were found to range from 70 - 40 kJ mol-1 (dependent on the potential). The model was further developed to account for the formation of the platinum binding sites (labelled as Pt BS) from precursor sites, Pt PS. A series of experiments employing phosphate buffers with a range of concentration and pH were performed. It was found that steady-state responses for the oxidation of H2O2 increased with increasing phosphate concentration. In the absence of phosphate, an alternative binding mechanism was evident. A maximum response was found at pH 6.8 and decreased markedly at more basic or acidic conditions. This pH-dependence suggested that H2PO4- was the species involved in the formation of the binding sites. The decrease in response at pH > 6.8 being caused by the decrease in [H2PO4-], whilst an inhibition of the precursor site by protons was proposed to account for the depression in electrode response at pH < 6.8. The influence of chloride upon the kinetics of H2O2 oxidation was examined and described qualitatively in terms of the new model. It was found that the rate of oxidation was decreased markedly in the presence of chloride. Two possible inhibition modes for chloride were identified and it was established that a non-competitive inhibition of the precursor sites was likely to be the dominant cause for the chloride inhibition. The work described in this thesis has not only identified a new and comprehensive mechanism for the oxidation of H2O2 at platinum electrodes, but also provides information that may prove useful when designing sensors that rely upon this reaction. In particular the important role of hydrodynamic conditions, buffer composition and concentration are clearly identified. Publications arising from this work i) Electrochemical oxidation of hydrogen peroxide at platinum electrodes. An adsorption-controlled mechanism. S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim. Acta, 1998 (43) 579. ii) Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Effect of potential. S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim. Acta, 1998 (43) 2015. iii) Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Effect of temperature. S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim. Acta, 1999 (44) 2455. iv) Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Phosphate buffer dependence. S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim. Acta, 1999 (44) 4573. v) Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Inhibitory effect by chloride ions. S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim. Acta, submitted for publication.Item Recent advances in technologies for vitamin A protection in foods.(Elsevier, 2008) Loveday, SM; Singh, HarjinderVitamin A deficiency affects many children in the developing world, and is preventable via food or pharmaceutical supplementation. The main technical barrier to the fortification of food with vitamin A is its susceptibility to oxidation and isomerization, which result in loss of nutritional efficacy. This review discusses recent technological avenues for stabilizing vitamin A in foods.