Celery is a herb specie containing natural components such as flavonoids that are considered significant for human health. They can help reduce the risk of some diseases like cardiovascular infections and tumors. As such, the global consumption of celery has rapidly increased over the years. To ensure the availability and undisrupted supply chain of celery products, the development of specific and highly efficient preservation techniques is a prerequisite. Among the available preservation technologies, super chilling that involves storing food below their freezing temperature, has been identified as a promising technology for celery preservation. Relative to freezing and refrigeration methods, super-chilling can largely maintain the biological cells’ living state, extend food shelf life, and consume less energy. However, whether super-chilling can be used to preserve fresh-cut celery effectively remains unclear.
In super-chilling preservation, the ice crystals formed within the foods provide the desired cooling to maintain the temperature balance and enhance the mechanical properties of the tissues. However, the ice crystals also influence the quality and structure of the preserved foods. They are affected mainly by the cooling rate. Several technologies, including immersion freezing techniques, have been employed to increase the freezing rate and improve food quality. For preserving fresh-cut celery, however, it is imperative to understand the impact of accelerating the cooling rate of fresh-cut celery through low immersion temperatures during super-chilling processes.
To this note, a team of researchers from Qufu Normal University: Dr. Cong-Cong Xu, Master De-Kun Liu, Dr. Chun-Xiao Guo, and Yu-qing Wu (Undergraduate) recently investigated the influence of cooling rates and super-chilling temperatures on ice crystals characteristics, cell structures, and quality of super-chilled fresh-cut celery. In this approach, different cooling rates at different immersion temperatures of -35°C, -45°C, and -55°C, as well as different super-chilling temperatures of 1-2 °C below the freezing temperature, were taken into consideration. Their work is currently published in the journal, International Journal of Refrigeration.
Based on the results, the average freezing temperature of fresh-cut celery was -0.48 ±0.08 °C, with a super-chilling degree freezing as -1.5°C and -3.0°C. The ultralow immersion temperatures significantly shortened the super-chilling temperatures and increased the cooling rate of fresh-cut celery. Interestingly, super-chilling to -1.5°C at -55 °C was reported to be the best for maintaining the cell structure and physicochemical quality of tissues attributed to the improved size, morphology, and uniformly distributed tiny ice crystals inside and outside the numerous cells. Moreover, the tissues exhibited enhanced mechanical strength that ensured adequate resistance to kinetic damages associated with packages and transport. On the other hand, other treatments resulted in larger and irregular ice crystals leading to severe deterioration of the cell structures and decreased quality.
In a nutshell, Dr. Cong-Cong Xu and colleagues examined the effects of cooling rates and super-chilling temperatures on the general quality of fresh-cut celery preserved through the super-chilling method. The obtained results provided evidence that supper-chilling can be applied to fresh-cut celery preservation under a combination of a super-chilling temperature of -1.5°C and a cooling rate of -55 °C conditions. These optimal conditions would be significant for achieving the desired qualities of super-chilled fresh-cut celery products.
Xu, C., Liu, D., Guo, C., & Wu, Y. (2020). Effect of cooling rate and super-chilling temperature on ice crystal characteristic, cell structure, and physicochemical quality of super-chilled fresh-cut celery. International Journal of Refrigeration, 113, 249-255.