Influence of temperature fluctuations on the state/phase, ice crystal morphology, cell structure, and quality of celery during frozen storage

The state diagram of celery and the influence of temperature fluctuations on its state/phase, ice crystal morphology, cell structure, and quality during frozen storage were explored. Temperature fluctuations changed the state/phase of frozen celery. The state diagram showed that frozen celery at glassy state (- 70 degrees C) changed into viscous flow state (T > -35.8 degrees C) and rubbery state (- 43.5 degrees C < T < -35.8 degrees C), and remained glassy state (T < -43.5 degrees C) at higher temperatures. Among frozen samples, those exposed to the viscous flow state (- 30 degrees C) and rubbery state ( - 38 degrees C) once every two days for a month showed the largest leakage of intracellular ions and losses of texture attributes and color. In contrast, those at the glassy state (-55 degrees C) and without temperature fluctuations (- 70 degrees C) showed the least losses. Smaller ice crystals and better maintained cell structures observed in the glassy tissues could account for these results. Hence, storing frozen celery below -49.3 degrees C appears optimal for retaining its quality and structure, whereas temperatures above -43.5 degrees C were potentially adverse conditions.