The use of a plug-flow model for scaling-up of spray drying bioactive orange peel extracts

• Spray drying of orange peel extracts was scaled up to a pilot-scale spray dryer.
• The plug-flow model was determined to be a useful method in the scale-up process.
• The plug-flow model predicted the moisture content for powders with < 15% error.
• The quality of the powders was kept in an acceptable range after scale-up.
• The retention of TPC and the SC50 of the powders were 88 ± 7% and 95 ± 8%, respectively.

The spray drying of orange peel extracts was scaled up from a laboratory-scale spray dryer to a pilot-scale spray dryer using two methods to predict the parameters of the spray-drying process. The mass and energy balance model predicted the outlet gas temperature, absolute humidity and the final moisture content of the particles with 5%, 2% and 74% errors, respectively whereas, the plug-flow model successfully predicted these parameters with < 1.5%, 1% and 15% error, respectively. The total phenolic content and the antioxidant capacity of the powders were retained to the extent of 88 ± 7% and 95 ± 8%, respectively, after the scale-up process. Therefore the plug-flow model was found to be a useful method in the scale-up process as a rapid estimation method for predicting the key parameters in spray drying with good accuracy, in order to keep the quality of the products within the required range.Industrial relevancePeels and seeds of citrus fruits, such as oranges, contain bioactive phenolic compounds that have demonstrated cancer-inhibition properties. However, due to their bitterness, they are not consumed and are considered to be waste material. The compounds can be extracted and turned into concentrated powder supplements. In powder form, these compounds can be easily incorporated in controlled and concentrated dosages into food formulae in order to create functional foods while masking the unpleasant taste. However, due to the heat sensitivity of these compounds, the minimum amount of heat treatment is required in the process. Spray drying, which is one of the fastest drying techniques available, can be used to convert these extracts into powders. However, spray drying these extracts is very challenging due to the presence of large amounts of sugars that cause stickiness and product loss during the process. In general, adding significant amounts of carriers to sugar-rich foods to overcome their stickiness during spray drying has been used in industry, compromising the purity of the final products. Moreover, in order to mass produce the powders, the process needs to be scaled-up. However, spray drying is extremely difficult to scale up using dimensional analysis (Oakley, 1994; Zlokarnik, 2003b). Computational fluid dynamic (CFD) simulations have been suggested as a powerful tool in this scale up of spray drying, but they are very time consuming. Therefore, if simpler models that do not require CFD simulations can adequately predict the process parameters, they can be used as fast estimation techniques for scale up. The results from this study guide the use of a plug-flow model for scaling up the process of spray drying orange-peel extracts while keeping an acceptable quality for the final product.