Application of radiofrequency heating and low humidity air for sequential drying of apple slices: Process intensification and quality improvement.

The present study aims at developing a low-temperature energy-efficient sequential drying approach, using
radiofrequency (RF) waves and low humidity air (LHA) for heat-sensitive foods like apple. Efficacy of employing
RF at primary (RF + LHA) and secondary (LHA + RF) drying stage with LHA was studied in comparison with
LHA and HA (hot air) and RF (2 A) drying, individually at 40 ◦C. LHA + RF reduced the drying time by 37% and
energy consumption by 52% compared to LHA. Apple slices dried with sequential LHA + RF approach well
preserved the polyphenols (98%), flavonoids (87%), and ascorbic acid (77%) compared to FD. Sequential drying
did not affect the color (ΔE = 7.4 ± 0.7) and also improved the rehydration ratio (3.9 ± 0.1). The principal
component analysis demonstrated that LHA + RF had higher retention of volatile compounds (aldehydes, esters,
acids, alcohols) than other studied methods. The study suggests that the application of RF at the secondary drying
stage with LHA accelerates the drying process and reduces energy requirement with better retention of product
quality attributes.