Effects of "antifreeze" oligopeptides and electric fields on unidirectional ice growth in thin water layers

The suppression of ice crystal growth is an important issue in several fields, such as food preservation in the food industry and the preservation of cells, tissues, and organs in medicine. The use of non-toxic additives, such as antifreeze proteins, is effective for this suppression. Oligopeptides, which are antifreeze protein segments, have recently shown unsatisfactory suppression of ice growth in solution. This study aimed to examine whether the suppressive effect of oligopeptides could be augmented by applying direct- and alternating-current electric fields. We conducted experiments by freezing an aqueous solution of oligopeptides. Successive images of the ice/solution interface were captured using a video camera. The interface velocities were calculated from the images. In the case of water, the interface velocities around the electrodes were lower than those between the electrodes. The latter interface velocities depended on the electric fields. These findings indicate that changes in the orientation of water molecules may contribute to these variations in interface velocities. In the case of the oligopeptide solution, the dependence of the interface velocities in the middle between the electrodes on the strength of the electric field applied was inconsistent with that for water. The interface velocities around the electrodes were different when an alternating-current electric field was applied. This resulted in the migration of oligopeptides caused by the electric fields. We predicted the lateral migration of oligopeptide aggregates in cases with intermittent direct-current and alternating-current electric fields, in which the electrostatic and induced forces varied in space and time. The changes in the lateral positions of the aggregates over time were more noticeable near the electrodes than between the electrodes. This noticeable migration may disturb the local growth of crystalline ice adjacent to the aggregates.