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    Studying the relationship between emulsion structure and lipid digestibility for infant milk : a thesis was present 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, 2020) Deng, Le
    Milk, whether maternal or formulated, provides the sole source of nutrition to infants in the early stages of life, providing critical micronutrients, support for the immune function and primary dietary macronutrients including lipids. In healthy adults, lipids are primarily digested in the small intestine. However, for infants, the neonatal small intestine is not fully developed after birth, so the gastric environment plays a more significant role in milk fat digestion. Clinical studies have shown that maternal milk fat is digested more efficiently than lipids in infant formulae in infants under infant gastric conditions. Compositional differences, the structure of the oil droplets, and especially the interfacial composition may all play a crucial role in influencing lipid digestibility in the infant's stomach. In this thesis, the simulated gastric digestion of model emulsions and commercial infant formula was studied. The model emulsions comprised either a phospholipid or complexed protein-phospholipid interface while keeping all other facets of emulsion properties equivalent. Gastric digestion of these emulsions was carried out across variable pH conditions using an analogue gastric lipase, alone and in combination with pepsin with findings providing insights into the role of each enzyme and their combined effect on gastric lipolysis. The rate and extent of lipolysis were characterised, along with morphological changes to the structure of the oil droplets. Results showed that gastric lipolysis might be influenced by pH conditions in the gastric environment when lipase was present alone in the simulated gastric fluid. The inclusion of pepsin resulted in significant structural changes when emulsions were stabilised with protein, in terms of droplet aggregation, size and morphology. However, no significant differences in the extent of lipolysis were determined. Thus, while the protein interface of both model and formulated emulsions was not observed to be a barrier for gastric lipolysis. Proteolysis of protein stabilised emulsions may lead to very different structural outcomes during gastric digestion when compared to phospholipid stabilised emulsions. While the research within this thesis demonstrates how the gastric environment influences emulsion structure as a consequence of interfacial composition, any specific relationship between structure and relative rate of gastric lipolysis currently remains undetermined. This research also highlights some of the ongoing challenges in the use of in vitro models to provide mechanistic understanding and interpretation of findings from clinical studies.
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    Evaluation of dry blending for infant formula manufacture : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology at Massey University
    (Massey University, 1989) Zhao, Zheng
    Blending experiments and storage trials were carried out to assess the feasibility of manufacturing infant formula through dry blending of high fat whey powder (HFWP) with whole milk powder (WMP) or a base powder (BP) made from skim milk, sucrose and corn oil. An indication of cohesiveness of the components of the blends was obtained by measuring compressibility using an Instron testing machine. Compressibility decreased in the following order: BP, wmp, HFWP, lactose and ascorbic acid. Particle size determination using a laser sizer indicated that the particle size increased in the above sequence. Scanning electron microscopy revealed no evidence of an ordered mixture for either whey powder with milk powder or the powders mixed with ascorbic acid. The mixtures did not exhibit complete randomness and segregation. They are thus termed 'pseudorandom mixtures'. HFWP was blended with WMP or BP to achieve a target ratio 50:50 in both an experimental ribbon blender and a pilot ribbon blender. Using Response Surface Methodology, load ratio and mixing time but not rotation speed were found to have significant effects on the homogeneity with the experimental ribbon blender. At load ratio 0.4, the time for reaching a certain homogeneity was shorter than that at load ratio 0.8. The cohesiveness of BP impaired its mixing. A mixing index based on a satisfactory sample standard deviation has an acceptable value of 1. Both powder ratio scores and ascorbic acid level could be mixed below a MI of 1.5 but above 1. As to protein, fat, carbohydrate, the mixtures reached the acceptable MI. The secondary nutritional requirements such as the ratio of whey protein to casein and the ratio of unsaturated fatty acid to saturated fatty acid were above 1 when the powder ratio MIs were higher than 1. After mixing WMP and HFWP for 10 minutes differences of sensory quality could not be detected by the taste panelists even though the MI was still above 1. Unblended and blended samples of WMP and HFWP were tested through a 180 day storage trial at 20°C, 30°C and 40°C. There was no significant difference between unblended and blended samples on the criteria of TBA, PV, HMF, oxidised flavour and caramel flavour at the 5% probability level. Using the Arrhenius approach, at 20°C, the shelf lives of unblended and blended samples were estimated as 1628 days and 1090 days respectively, with an oxidised flavour limit of 3.5 out of 7 points. The shelf lives were 480 days and 466 days based on a PV limit of 2 milliequivalents O2 per kg fat. Dry blending is a feasible technique for manufacturing infant formula, with acceptable homogeneity of the main components of the blended samples and with normal storage stability. The cohesiveness of the components and the design of blender are important factors in improving homogeneity. Further trials are recommended in both experimental and commercial plants.
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    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-Han
    Oxidative 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.
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    A quantitative model for the design of a processed infant food product for Thailand : a thesis presented in partial fulfilment of the requirements for the degree of Ph. D. in Product Development at Massey University
    (Massey University, 1977) Chittaporn, Patchree
    A quantitative model was developed to design a processed infant food product for Thailand. Linear programming was used as a basis for the model. The model can select not only the raw materials but also the process, taking into consideration the nutritional requirements of infants and the product acceptability. Furthermore, any changes in the raw materials, process and product quality can be easily studied with the model. The model was developed in three consecutive steps. Firstly, the Thai infant's nutritional requirements, and the compositions and costs of suitable indigenous Thai raw materials were included in the linear programming model. Secondly, the effect of heat processing on the destruction of the required nutrients was considered for different processes and the nutritional constraints in the model were modified to allow for the losses during processing. A mixture of raw materials was chosen by the model for each process and the most suitable combination of process and raw materials was selected. Finally, eating qualities were included in the model which enabled the model to select the raw materials not only subject to the modified nutritional constraints but also to the required eating quality. To include the losses of nutrients during heat processing, data on the destruction of nutrients by heat processing were collected from the literature to predict the reaction rate constants at different temperatures. First order reaction kinetics were assumed. The Arrhenius relationship between the reaction rate constant and the reciprocal of the absolute temperature was found to be generally true for the destruction of all vitamins and essential amino acids. The losses of vitamins and amino acids during a process were thus calculated from the Arrhenius relationship using the time and temperature history of the process. By including these losses of nutrients into the nutritional constraints in the model, their effects on the nutritional composition and cost of the formulation were compared for different processes and a choice was made of the most suitable process. Several cooking and dehydration processes which could be used for infant food processing in Thailand were compared and batch cooking followed by drum drying was found to be best. Consumer evaluation of the drum dried product suggested a need for improvement in the taste and colour of the product. Constraints restricting the selection of sugar and of raw materials with strong colours were included in the model, and a more acceptable product was obtained. This model can be used not only to formulate an acceptable mixture of raw materials for any process but also to compare different processes for the production of an acceptable and cheap infant food.