Scale-Up of the Spray-Drying Process for Bioactive Fruit Extracts

Abstract

Spray drying is a rapid drying technique used in the food industries to convert heat-sensitive materials into powders. However, spray drying sugar-rich materials, such as fruit juices and extracts, is very challenging due to the stickiness of these products. Moreover, scaling up the spray-drying process cannot be performed by using simple dimensional analysis due to the complexity of the process. In this study, first the best operating conditions for spray drying orange-peel extracts have been determined. Also the best method to overcome the stickiness of the powders and enhance the process yield has been determined. Then the process has been scaled up from a small-scale spray dryer to a pilot-scale spray dryer. Two methods have been used to predict the key results from spray drying after scale up; a mass and energy balance approach and a plug-flow model approach. Based on the results found in this study, it has been suggested that the plug-flow model is a useful method in the scale-up process as a rapid estimation method for predicting the outlet gas temperature, the absolute humidity and the final moisture content with acceptable accuracy, in order to keep the quality of the products within the required range. Finally, a new spray dryer was designed and built in this study, based on the previous findings in the drying technology group and available reports in the literature, in the workshops of the School of Chemical and Biomolecular Engineering at the University of Sydney. The new design has many advantages compared with conventional designs such as different plenum chamber that contributes to decreasing the wall deposition. The new spray dryer has a different geometry at its inlet that causes different and more complicated air flow patterns that may affect the drying rate of the droplets, significantly. Spray drying orange-peel extracts was successfully scaled up to this new design, too.