MARKET DISEASES OF FRUITS AND VEGETABLES 27 



FREEZING INJURY 



Investigations by the Bureau of Plant Industry indicate that Wash- 

 ington Navel oranges freeze at 26° to 28° F., Thomson Navel at a 

 little higher temperature, Valencia at 26.5° to 28.9°, and lemons at 

 27.9° to 28.5°. 



THAN SIT FBEEZES'G 



Freezing injury in transit is likely to occur in the fruit next to the 

 side walls and along the floor of the car. rather than in fruit in the 

 body of the load. It seldom shows in the form of drying out so char- 

 acteristic of fruit frozen on the tree. Oranges are often bitter in 

 flavor for a time after thawing, but this is not a consistent factor. 

 If the freezing has been severe, the rind may show effects ranging in 

 severity from almost typical brown stain to leaden-gray discolored 

 areas of varying size, which greatly resemble watery break-down. 

 The affected rind tissues may or may not be sunken, but when severely 

 frozen they usually become soft and mushy and are underlain by 

 mushy pulp tissue (see Grapefruit, Watery Break-down, p. 10). 



Freezing damage is best seen by cutting off both ends of an orange, 

 then cutting through the rind of the central portion remaining, and 

 pulling the segments apart. If the fruit has been frozen the mem- 

 brane between the segments will show a soaked condition and usually 

 a number of white specks, which are hesperidin crystals (maringin 

 in grapefruit) resulting from the freezing (pi. 16, C). However, 

 the presence of hesperidin crystals in oranges is not necessarily an 

 indication that the fruit has been frozen. They may also result from 

 the application of heat to the fruit or from rapid drying out of the 

 tissues. In tangerines the hesperidin crystals occur in the pulp as 

 well as on the segment walls and are seen even more readily than in 

 oranges when a cross-section cut is made. Freezing damage may be 

 confined to a part of the fruit, in which case the signs suggested will 

 be found in the affected part. The method of examination just de- 

 scribed is particularly useful for California oranges. Florida oranges 

 are not so easily examined in this way but are more likely to show the 

 mushy condition in cross section. 



Lemons and grapefruit show the damage in cross section much more 

 plainly than oranges, although it is desirable at times to pull grape- 

 fruit sections apart as recommended for oranges. If lemons have been 

 seriously damaged the pulp becomes mushy at once after thawing. 



Grapefruit shows, in addition to the symptoms just described, a 

 milky appearance of the pulp, which is in marked contrast to the very 

 light amber color and the almost transparent condition of unfrozen 

 pulp. The contrast is especially noticeable in fruits that have been 

 frozen in small spots or only on one side. The milky appearance of 

 the pulp is also found in grapefruit that has been in storage for 8 to 

 10 weeks and may be accompanied by a bitter taste. However, such 

 fruit is not mushy and watery unless affected by watery break-down ; 

 in such a case, a positive diagnosis must depend on a consideration 

 of the history of the fruit and the conditions under which the injury 

 is found. 



FRETT FROZEN OX THE TREE 



Citrus fruit frozen on the tree shows a number of symptoms de- 

 scribed under transit freezing, if examined soon after the freezing 



