Crystallization Changes Of Grape Cells And Changes Of Phase Transformation During Freezing-Thawing Process

With the improvement of living standards, people are more concerned about the quality of fruits and vegetables, especially quality requirements of fruits and vegetables in refrigerated process. However, fruits and vegetables are also constantly engaged in the process of thawing during freezing. The crystallization and phase transformation of fruits and vegetables is worth to study. Red grape as experimental subjects is used to test the crystallization and phase transformation of fruits and vegetables during freezing- thawing process. Ⅰ.Changes in crystallization of grap cell were investigated during freezing- thawing process with the low temperature stage from the microscopic point.Grape slices are tested with different rates during freezing – thawing process by low temperature stage system including information collection-computer storage, temperature control systems, microscopes, the CCD(Charge Coupled Device) and BCS-196 cold station. Microscopic images are analyzed to find the law of ice growth and melting characteristics, as well as changes in grape cell volume, internal pressure, and permeability. Ⅱ.Changes in phase transformation of grap were investigated during freezing- thawing process with the DSC(Differential Scanning Calorimetry) system from the latent heat point.Grape pulp are tested with different rate, frequency, time interval, the rate of the gradient and the rate through maximum ice crystal generation zone during freezing – thawing process by DSC scanning calorimeter(including computer data collection system, and high-purity nitrogen used to purge the sample). Heat flow graph are analyzed to find the law of latent heat, the end point of the phase transition, transformation starting point, as well as changes in parameters such as phase transition peak.The law of crystallization and phase transformation during freezing- thawing process is found with low temperature stage system and DSC system: the lower the rate of freezing, the greater the corresponding freezing point temperature, During the process of thawing with an increase rate, the peak point of the phase transition temperature, the end point of the phase transition temperature and the latent heat value will increase.