Individual and synergistic effect of multi-frequency ultrasound and electro-infrared pretreatments on polyphenol accumulation and drying characteristics of edible roses

The freeze-dried (FD) edible roses with high content of bioactive substances and superior flavor have been favored by consumers. Nevertheless, the development of freeze-dried rose industry has been plagued by a long drying time and low efficiency. This study investigated the effects of ultrasonic pretreatment (UP) in multi-frequency modes and electro-infrared pretreatment (EIP) prior to FD on polyphenol accumulation and drying characteristics of roses. The mechanism was explored by the changes in microstructure, equivalent circuit pa-rameters, and phenol identifications of rose. The results showed that the FD time of roses decreased by 26 % after ultrasonic-infrared sequential synergistic pretreatment (UP + EIP) due to the damage of cell membrane permeability from UP. The quality attributes of UP + EIP products including color, phenols, and antioxidant activity (DPPH and ABTS radical scavenging rates) remarkably improved. UP + EIP significantly (p < 0.05) increased the content of polyphenols, namely quercetin-3 beta-D-glucoside, phlorizin, procyanidin B2, gallicacid, and rutin in the FD roses quantified by ultra-high performance liquid chromatography-quadrupole time of flight mass spectrometry (UPLC-qTOF-MS/MS). Therefore, UP + EIP is an effective pretreatment method for shortening FD time and producing high-quality FD rose products with enhanced polyphenol content.