Drying kinetics and chemical profile of propolis extract from Heterotrigona itama

The present study investigated the effects of drying on the quality of propolis from Heterotrigona itama reared in a jaboticaba plantation. Raw propolis was extracted using 70% aqueous ethanol in an ultrasound assisted extraction system. Then the propolis extract was subjected to three drying techniques, namely sun drying, vacuum oven drying and infrared drying. The drying behavior of propolis was found to follow thin layer models. The page model was the most suitable drying model with the kinetic constants of 0.0014 g/hr (sun drying). 0.0794 g/hr (vacuum oven drying) and 0.0675 g/hr (infrared drying). A diffusion controlled process was the dominant drying mechanism of propolis in the vacuum oven and infrared dryers because only two falling rates were observed. However, sun drying of propolis extract occurred at a constant rate in an open air system. Although the vacuum oven and infrared drying accelerated the drying process, some phenolics and flavonoids were degraded to some extent, thus lowering the antioxidant capacity of propolis extract. The reduction was partly due to the degradation of flavanones, particularly for infrared dried propolis extract. Unsupervised principal component analysis also revealed that propolis extracts formed two distinct clusters, in which sun dried propolis extract was located far away from the other propolis extracts. Mass spectra indicated that higher levels of lignin based phenolics, coumarins, and their glycosylated derivatives in sun dried propolis extract were the main contributors to the variance. The findings concluded that the vacuum oven was the best drying technique for propolis with good quality.