Evaluation of mechanical properties, heating rate and radio frequency explosive puffing (RFEP) quality of purple sweet potato under different moisture contents and moisture equilibrium process

Abstract

The effects of different initial moisture contents (15–55%) and moisture equilibrium process (MEP) on the mechanical properties of the gas-blocking surface layer of purple sweet potato chips and the radio frequency (RF) heating rate, uniformity, and radio frequency explosion puffing (RFEP) quality were discussed in this article. Low-field nuclear magnetic resonance indicated that hot-air pre-drying reduced the amount of free water and caused the transfer of immovable water to bound water. This process was accompanied by an increase in the thickness and elastic modulus of the gas-blocking surface layer, resulting in a significant increase in the RF heating rate and uniformity. Prolonged RF heating time led to a decrease in anthocyanin content. The results demonstrated that the puffing rate initially increased and then decreased with increasing initial moisture content. The puffed sample with an initial moisture content of 45% exhibited the highest puffing rate, crispiness, and porosity. X-ray micro-tomography results reveal that MEP improved the morphology of puffed products, ensuring even distribution of small pores and reducing the presence of hard edges. In conclusion, considering the heating time and anthocyanin retention rate, the initial moisture content ranges from 35% to 45% after MEP was the best pre-treatment.