Emerging pulsed electric field and oscillating magnetic field combination technologies on food freezing

M.S. University of Hawaii at Manoa 2013.Includes bibliographical references.Recently, new emerging freezing technologies have been developed to alternate traditional and inefficient freezers. However, due to water crystallization, the consequence of freezing and thawing that can impact on quality of food composition and microstructure remains as critical issues. In present study, combination of pulsed electric field (PEF) and two different types of magnetic fields were applied to resolve the outstanding freezing problems. The concept was that when a polar liquid (i.e. water) is exposed to an external electric field, it would undergo polarization that re-orientates and vibrates water molecules. Also, water is diamagnetic which may develop a magnetic dipole moment in quick response to an applied magnetic field, leading to rearrangement of water molecules. Thus, combination of these two field strengths was hypothesized to effectively interrupt critical ice nucleation in food matrices and extend the supercooling status of foods even at subzero temperatures. As a result, the growth pattern of ice crystals and phase transition time of 0.9% NaCl solution were investigated and compared under individual and combination of PEF (1.78 V/cm, duty cycle: 0.5) and static magnetic field (SMF). The combination effect of PEF at 20 kHz and repulsive SMF treatments at a freezer temperature of-20°C showed an increased number of the finest and round ice crystals (equivalent diameter: 97 ± 12 μm; roundness: 0.90 ± 04; elongation: 1.24 ± 0.33) during the shortest phase transition time (1004 ± 3 sec). The second approach included an innovative maintenance of fresh food qualities (i.e. chicken breasts) by establishing a stable supercooling state by combination of PEF and oscillating magnetic field (OMF). Supercooled chicken breasts preserved at-7°C for 12 hours showed little apparent food tissue damages and the overall degrees of qualities deterioration (i.e. drip loss, color, texture, pH and lipid oxidation) were significantly lower than control samples in refrigeration and freezing storage. The developed technology will have the potential to ensure food quality and freshness during storage, which would have an enormous impact on food industries