Antioxidant capacity of spray-dried plant extracts: Experiments and simulations

The effects of different inlet air temperatures (70–150 °C) have been studied on the antioxidant retention and yields of a spray-dried bioactive solution (Hibiscus sabdariffa L.) from a Buchi B-290 spray dryer and compared with plug-flow spray drying simulations. Antioxidant retention has been tested using the Oxygen Reducing Antioxidant Capacity assay (ORAC). Experimentally, a peak yield of between 65% and 70% of the solids fed to the dryer has been found at an outlet gas temperature of 60–65 °C and an inlet air temperature of 110 °C, regardless of the batch of material or the liquid feed rate. The varying outlet gas temperatures did not significantly affect the antioxidant retention of the sample, and the simulations demonstrate that this result is due to the competing effects of increasing air temperature and decreasing water activity (at higher inlet air temperatures) on the degradation kinetics. These results suggest that it is more important to obtain greater product yields rather than minimising the degradation amount in this spray-drying situation.