Evaluation of strawberries dried by radio frequency energy

Dielectric processing has recently attracted attention in both agriculture research and industry as an efficient heating/drying method. Dielectric processing includes drying by radio frequency (RF) and microwave drying (MW). The characteristics of RF dried strawberries were evaluated and compared to hot air drying (AD), freeze-drying (FD) and MW drying. Our results showed that dielectric drying was superior in terms of drying rate. The total drying time of MW and RF were 40 and 55 min, respectively, compared to 100 and 1,320 min for AD and FD, respectively. Compared to MW drying, RF drying offered better uniformity of temperature distribution and energy transformation. RF dried strawberries also had superior color compared to AD and MW, as well as greater retention of carotenoid, anthocyanins and total phenolics, the quality of RF dried samples was close to FD samples. SEM photos indicated RF dried samples showed better quality (smoother surface) than MW. Flavor analysis showed that all drying methods reduced aromatic substances.