Observation And Study On The Characteristics Of Simulated Freezing Injury Of Apple Fruit

During storage,apple fruit often occurs like watercore disease,tiger skin disease,cold injury,and freezing injury.Physiological diseases have severely affected the storage quality of apples.There are many researches on pre-harvest apple frost damage in China,and there are few studies on the occurrence of freezing injury during storage.In this paper,based on the problem of frozen storage of apple fruit,we selected Gala,Jonagold,Fuji apple as the test materials to study the critical time of simulated freezing injury at-4°C,and explored the thawing at room temperature,thawing at 4°C,and gradient temperature rising and thawing(first the frozen apples were reached at 0°C for 24 h,then with a temperature rise of 1°C per day until 4°C),and the following conclusions were obtained when the effects of the three thawing methods on the quality and physiological indexes of frozen apples:(1)Determination of critical time: At-4°C,the critical time for cold injury at the level 2 of Gala,Jonagold,Fuji apple was 60 h,72h,96 h respectively;the critical time for occurrence of 3rd frost injury was 168 h,192h,216 h respectively.From the critical time,it can be seen that the tolerance of three varieties of apple to freezing injury: Fuji> Jonagold> Gala.(2)The gradient thawing method and the 4°C thawing method can effectively reduce the fruit weight loss rate and the loss of nutrient components in fruits compared with the room temperature thawing method.The weight loss rate of fruits treated by gradient thawing method is slightly lower than that of the 4°C thawing method.Both of them can increase the activities of fruit protective enzymes but their characteristics are different.Gradient thawing method can increase significantly the activities of the three protective enzymes of three apple varieties,and the 4°C thawing method only increased the SOD activity of Jonagold and the POD activity of Fuji.Gradient thawing method and 4°C thawing method reduced the damage of the cell membrane system.Both the thawing method and the 4°C thawing method can reduce the shelf-life browning rate and rot rate compared with the thawing method at room temperature,but the browning index and rot rate of the apple fruits treated by the gradient thawing method are the lowest.Damage to the tissue structure of the fruit cannot be repaired by thawing.The thawing method has no effect on fruit firmness.In conclusion,gradient thawing method can reduce or even avoid the quality deterioration and quality reduction caused by freezing injury.The effect is significant and is better than the other two methods.The 4°C thawing method,although not as effective as the gradient thawing method,is easy to operate and easy to promote in production.