Spray Drying Engineered Milk Sugar and Protein Powders with High Porosity or Controlled-Release Properties for Food, Pharmaceutical and Energy Applications

Abstract

Australia is a major dairy exporter with multiple milk and dairy products at relatively low prices locally and high annual output, making it attractive to further engineer the products for more applications rather than just simple foods. Regular milk contains milk sugar (lactose), milk proteins (casein and whey), fats, minerals and a few other ingredients. In this thesis, lactose, casein and whey proteins have been used to develop novel materials for food, pharmaceutical and energy applications based on spray-drying technology. Starting with lactose, where a porous structure has been previously developed and used as drug carrier, a micro-meso-macroporous lactose with a unique and uniform shape (flower-like) has been engineered in this work by modifying the operating conditions of spray drying and templating technique. The synthesis of the flower-like lactose involves two steps, namely spray drying followed by ethanol washing. Porous flower-like lactose has been produced with a high surface area and a high pore volume, and these values, along with other characteristics, vary with different operating conditions and/or using different templating agents. The effects of some typical operating conditions have been studied for producing flower-like lactose and its capacity for drug loading. It has been found that, by altering the interior structure of the flower-like lactose particles, the position of loaded drug molecules can be controlled either at the core, the region between core and shell, or the shell. By tailoring the pore structure based on the differences, in the diffusion coefficients of the templating agents compared with the diffusion coefficient of lactose, the flower-like lactose particles with a porous-core-solid-shell or solid-core-porous-shell structure have been engineered, giving different dissolution profiles of drugs loaded in the particles. Casein, isolated from milk, is one of the widely used natural products in the food industry, and has been targeted as the second main material to be engineered for controlled release applications in this thesis. For the first time, casein has been acidified at a pH of 1.0, forming a shampoo/lotion-like gel, which has been further processed by spray drying and tableting for controlled-release applications. Typically, microencapsulation of ascorbic acid (vitamin C), coffee and acetaminophen (for pain relief) by the casein gel has been carried out using spray drying for controlled release. After tableting, the controlled release of the ingredients from the casein gel tablets has been achieved, with the release period lasting from a few minutes to over a few days by changing the operating conditions. Moreover, WPI (whey protein isolate) has been used along with the casein gel at different ratios as the shell materials in the spray-dried particles for the controlled release. The heat treatment has been applied to the milk protein tablets, showing that the overall release period may be further extended (over two days) as long as the protein has been denatured. To develop an energy application for milk products, raw whey powder, as a by-product of the cheese and casein production process from an Australian manufacturer, has been used as the source of porous carbons and engineered for capacitive energy storage. Spray drying has been used to produce uniform composite particles containing whey powder and KOH, in which KOH serves as an activation agent to create uniform pores during carbonization, and the proteins in the whey powders act as N dopants. The produced carbons have a large specific surface area and deliver a good specific capacitance. Electrochemical impedance spectroscopy analysis indicates that the carbon material has a good ionic conductivity at the electrode-electrolyte interface and efficient diffusion of electrolyte ions into its bulk. A two-electrode symmetric supercapacitor has been assembled, which is comparable with other carbon-material based supercapacitors. The findings from this thesis show that the milk sugar and proteins can be developed for novel food, pharmaceutical and energy applications, possibly benefiting a further growth and development of the current dairy industry. The achievements may have innovative contributions for making tailored particles, controlling release and producing porous carbons from benign ingredients and low risk processes. Future works based on these findings may be performed for advanced material analysis, scale up, drug formulation, in vivo and clinical tests, and assembly of real electrical devices, to analyse the practical feasibility of these fundamental concepts.