The Mechanism And Study Of Droplet Surface Formation Of The Emulsion Particles During Drying

Spray drying is widely used in the food industry as a rapid dehydration technology to produce powdered products, such as milk powders, DHA powders, protein powders, etc. The optimization of powder quality is usually achieved by adjusting the operation conditions of the spray dryer, or by adjusting the composition of feed liquid. However, the transition process from droplets generated by the nozzle at the top of a spray dryer to the particles collected at the bottom outlet can be regarded as a black box process. The structure of a spray drying tower makes it difficult to take samples of the droplet being dried and to conduct real-time analysis of samples. The optimization of powders quality often relies on empirical experimentation. There still lacks understandings about the mechanisms of particle drying process and the particle formation behavior.The present project utilized a single droplet drying(SDD) apparatus to analyze the drying behavior of emulsion droplets with different compositions under conditions simulating spray drying processes. Emulsion containing different types of fat/oil was prepared and dried under identical conditions to study the different surface formation behavior during drying. The effects of emulsion composition on the particle functionality development during drying were investigated. Furthermore, kinetics parameters(temperature, diameter, weight) of emulsion droplet during drying were experimentally determined for three types of emulsion made of different fat/oil. The study provides in-depth understanding for the drying behavior of emulsion droplets as affected by different fat/oil components.The development of particle surface wettability during droplet drying of whole milk with food-grade surfactant was firstly investigated. Three types of whole milk were prepared, i.e., original milk, original milk with 0.1 wt.% Tween 80 addition and original milk with 0.1 wt.% Lecithin addition. For each type of milk, the drying processes of milk droplets were stopped at different stages; then a single water droplet was attached to the semi-dried milk droplet as in-situ rehydration test to observe its surface wettability. The effects of surfactant addition on the surface wettability were investigated for both original whole milk and high solids whole milk. It was found that during drying of high solids milk, the wettability improvement due to surfactant addition was not as prominent as the drying directed towards the development of powder surface wettability, one of the most important powder quality criteria, as drying progressed. The study explored the main factors affecting the emulsion drying and the underlying scientific mechanism. The findings would contribute new insights towards the production of formula milk powders in diary industries. of original milk. The difference observed between high solids and original milk drying was attributed to the different shell formation behavior. High solids milk contained less water, leading to a comparatively rapid drying process with early surface shell formation, which likely limited the possible migration of surfactant molecules to the surface.Secondly, the present study investigated the drying behavior of artificial milk emulsion and the improvement of particle surface wettability due to surfactant addition. The major components of whole milk are lactose, protein and fat. Three types of artificial milk emulsion were prepared following the proportion of original whole milk with different fat/oil components, i.e., Liquid oil, butter and lard. The surface wettability of emulsion droplets with varied initial solids content at different drying stages were experimentally investigated with and without surfactant addition. The results of SDD experiments showed that the drying behavior of artificial emulsion was of large difference to original whole milk, irrespective of the type of fat/oil used. According to in-situ rehydration test, emulsions with and without surfactant addition did not show significant difference in the development of particle surface wettability during drying, which was also different to the results of whole milk experiments.To further understand the effects of different fat/oil components on the drying behavior of artificial milk emulsions, the present study also quantitatively investigated the drying kinetics of the three samples during drying. There drying air temperatures were used i.e., 70, 90, and 110°C. At each temperature, the droplet temperature change,volume change and mass change were measured using the SDD apparatus for each emulsion; based on the changes in droplet diameter and moisture content were calculated. The results showed that the drying kinetics of the three types of emulsions were also relatively similar. Though the particle distribution analysis showed that the oil droplet sizes in the three samples(artificial emulsion prepared with liquid oil, butter and lard) were of great difference, the drying behavior of the emulsion was minimally affected by the different size distributions. The similar drying kinetics between the three types of emulsions was in accordance with the similar shell formation behavior reported above, indicating that the use of three types of fat did not show remarkable influence on the drying behavior of artificial milk emulsions.In summary, the present study provides a large number of scientific data on the drying behavior and shell formation process of dairy emulsions. Significant attention has been...