PROBING THE PARTICLE FORMING BEHAVIOUR OF DHA CONTAINING EMULSION DROPLETS USING A SINGLE DROPLET DRYING DEVICE

摘要

Spray drying is a primary method for manufacturing food powders today.Before subjecting a new formulation to this process, information about drying kinetics and shrinkage parameters, which are crucial to model the spray drying process, can be obtained through single-droplet drying experiments. The single droplet drying rig is specially designed to allow accurate measurement of droplet size, weight, and temperature during drying.In this study, the glass filament method (Lin and Chen, 2002; Lin and Chen, 2004) was implemented to measure the above-mentioned three parameters of emulsion liquid droplets (containing DHA oil) with different shell materials (protein-based and starch-based, respectively) at specific solid-liquid ratios under air convection.Even though there are many reported works on DHA microencapsulation, there has been a lack of fundamental information of the processes.It was found that the weight and size of the droplets decreased sharply due to water evaporation, while the droplets temperature remained at a wet-bulb like temperature.While the moisture content of the droplet continued to decrease as drying proceeded, the transfer of moisture within the droplet/particle became restricted by the solid matrix formed.In the meantime, the droplet temperature gradually approached the air temperature as drying continued while the diameter and weight each reached a plateau.Based on these data, the Reaction Engineering Approach (REA) (Chen and Xie, 1997; Patel & Chen, 2008; Chen, 2008) could be adopted to describe the drying behaviour of encapsulated DHA droplet. The shrinkage coefficients were obtained and correlated against the solids content.Discussion based on visual observations on the emulsion morphologies and droplet drying behaviours are presented. This study is a start of a series of fundamental investigations aiming to understand the drying behaviour in relation to particle functionality of encapsulated DHA particles.