Effect of dry-blanching pretreatment and drying using radio frequency energy on the dehydration performance, structural and quality properties of tiger nuts

Radio frequency (RF) heating as an innovative mean of blanching pretreatment has the ability to improve product quality and efficiency in the drying process of agricultural products. This study clarified the mechanism involved in the synergistic effect of RF dry-blanching (RFDB) pretreatment (0–8 min) combined with different drying methods (including hot-air drying (HD) and RF assisted hot-air drying (RFHD)) on the drying characteristics, microstructures, and chemical qualities of tiger nuts. The results demonstrated that compared to the unpretreated samples, the RFDB pretreatment not only caused a reduction in moisture and relative enzyme activity during a short period of time, but also altered the moisture distribution, diminished moisture mobility, and provided a more uniform moisture distribution within the tiger nuts. The RFDB pretreatment significantly shorted the drying time of HD and RFHD by 7.78–22.22 % and 7.14–18.10 % respectively ( p < 0.05), and reduced the energy consumption of RFHD and HD by 7.98–20.89 % and 6.58–17.65 %, respectively. Following RFDB pretreatment, the crystal structure and cellular structure integrity of tiger nuts were damaged, and the phenolic and flavonoid contents significantly increased. But the phenolic and flavonoid compounds were degraded due to temperatures of higher than 80 °C with 6–8 min of RFDB pretreatment times. These outcomes revealed the positive effects of proper RFDB pretreatment on the drying process of tiger nuts and may provide novel insights and technical support for improving the drying efficiency and product quality. • Radio frequency dry-blanching (RFDB) pretreatment effectively inactivated enzymes. • RFDB pretreatment changed the moisture status and distribution of tiger nuts. • RFDB and RF assisted hot-air drying reduced treatment time and energy consumption. • Quality characteristics of dried tiger nuts were enhanced by RFDB pretreatment.