Combined vacuum osmotic dehydration by pomegranate juice concentrate and hot-air assisted radiofrequency drying to produce fortified orange slices

In this study, vacuum osmotic dehydration (VOD) with pomegranate juice concentrate was applied to produce orange slices with high bioactive compounds. The optimum VOD process conditions were selected by response surface methodology (RSM) as 65° brix of pomegranate juice concentrate, 4:1 (g/g) pomegranate juice concentrate to orange slices, and 30 min of vacuum time to obtain a higher water loss of 40.52 ± 1.31%, solid gain of 21.57 ± 0.85%, and weight reduction of 18.60 ± 0.93%. After VOD, the osmotically dehydrated orange slices were dried by hot air-assisted radiofrequency drying (HA-RFD) and conventional hot air drying (HAD). The results demonstrated that HA-RFD increased the rate of drying with a 62% decrease in drying time compared to HAD. Bioactive compounds of dried samples were assessed and compared with the fresh orange slices. The osmotically dehydrated and HA-RF dried samples had higher TPC (1496 mg GAE/100 g dw), TFC (415 mg rutin/100 g dw), and antioxidant activity (90%) than the fresh samples (TPC of 948 mg GAE/100 g dw, TFC of 397 mg rutin/100 g dw and antioxidant activity of 77%) due to the high level of bioactive compounds that present in the pomegranate juice concentrate. Lower retention of bioactive compounds was obtained for the samples dried by HAD compared with the fresh and HA-RF dried samples. To the best of our knowledge, this is the first study to combine pomegranate juice concentrate with orange slices prior to HA-RFD, offering a novel strategy for the development of citrus-based functional snacks with improved nutritional quality and industrial drying efficiency.