Microwave‐induced free radicals production in red wine and model wine by electron paramagnetic resonance spin trapping

Microwave can directly induce the production of 1‐hydroxyethyl free radical in red wine and model wine. Free radicals are considered as key intermediates in the wine aging processing by microwave, but their properties have not been determined. Electron paramagnetic resonance (EPR) spin trapping with 5,5‐dimethyl‐1‐pyrrolin N‐oxide (DMPO) was used to detect the type of free radicals. After microwave irradiation, spin adducts of hydroxyl free radical were detected in DMPO solution, whereas 1‐hydroxyethyl free radical spin adducts were captured in red wine and model wine, because 1‐hydroxyethyl free radicals arose from the oxidation of ethanol by hydroxyl free radical in red wine induced by microwave irradiation. Compared with the processing of natural oxidation, the intensity of free radicals induced by microwave in red wine became more strong, and the effects of microwave temperature, time, and power on the intensity of 1‐hydroxyethyl free radical spin adducts in model wines were also studied. The intensity of free radical spin adducts increased with the increasing of microwave power and time. The intensity of DMPO/1‐hydroxyethyl free radical spin adducts increases at low temperature, but decreased at higher temperatures. PRACTICAL APPLICATIONS: This study investigated the existence of free radical in the processing of wine aging, and the possible mechanism of microwave irradiation accelerated aging of red wine was studied with model wine. Results revealed that the intensity of 1‐hydroxyethyl free radical induced by microwave in red wine and model wine. Therefore, microwave irradiation was considered to be a promising aging technology, so microwave radiation technology can be used in many aging products that sped up the aging processing.