Reducing atmosphere drying as a novel drying technique for preserving the sensorial and nutritional notes of foods

Reducing atmosphere drying (RAD) was assayed as a novel technique for preserving the color and the nutritional fresh notes of apricot. A freeze, hot air and vacuum drying techniques were applied for a comparison purpose. The results showed that the apricot samples dried by both RAD_MIX and RAD_NITROGEN preserved better the fresh color notes while the freeze-drying was characterized by light and dully notes compared to a fresh sample. The total phenolic content significantly differed between fresh, RAD_MIX, RAD_AIR, hot air and vacuum with the highest value observed for both vacuum and hot air with 284.8 and 259.5 mg GAE 100 g^-1 dm, respectively. DPPH inhibition activity was significantly similar for both fresh (or freeze drying) and each RAD_MIX, hot air and vacuum dried samples with 83.52, 76.3, 70.31, 67.86%, respectively, with the highest value attributed to RAD_MIX sample. The RAD-type dried samples (RAD_MIX, RAD_NITROGEN, RAD_AIR) possessed ABTS scavenging activity range of 68.74, 64.49 and 61.61 μmol TE g^-1 dm respectively, which were close to that of the fresh sample (63.36 μmol TE g^-1 dm) with the highest value attributed to RAD_MIX sample. The total flavonoid content was significantly similar between fresh (or freeze drying), vacuum, hot air and RAD_MIX samples with a range of 27.38, 24.25, 19.41 and 18.81 mg QE 100 g^-1 dm, respectively, which exhibited an advantageous role of hydrogen in RAD_MIX system over both RAD_NITROGEN and RAD_AIR. For the first time, a technique based on the use of hydrogen in the drying atmosphere of a closed system was successfully proved for drying foods. This novel technique exhibits an opportunity for the food drying processors to produce dried foodstuffs with fresh color and nutritional notes.