Effects of extremely low frequency electromagnetic field on the freezing processes of two liquid systems

Freezing process assisted by electromagnetic field is one of the emerging novel food freezing technologies. The present study investigated the effects of extremely low frequency electromagnetic field (ELF-EMF) on the freezing process of two aqueous solutions with different solutes of 9 g/L sodium chloride (physiological saline) and 10 mmol/L PDADMAC (poly dimethyl diallyl ammonium chloride). Freezing parameters such as supercooling degree were determined in different frequency bands, and some parameters of thawed samples were also measured. Results showed that the supercooling degree of physiological saline was decreased and that of PDADMAC solution increased first and then decreased, while the images of ice crystals showed more and deeper cracks created in some treated samples. The surface tension and contact angle indicated that the energy balance of samples was disturbed under ELF-EMF, and the infrared and Raman spectra of the treated PDADMAC solution showed that the polarized feature and dipole moments of macromolecular groups were enhanced, which might contribute to the change of the freezing process.