POSTHARVEST CALCIDM TBEATMEMTS: REDUCIHG THE RISK OF FRUIT DAMAGE 



William J. Bramlage, Sarah A. Weis, and Patricia A. Shesgreen 

 Department of Plant and Soil Sciences 

 University of Massachusetts 



Recently, we re-examined the potential benefits and risks from using 

 postharvest calcium (Ca) treatments ( Proc. Mass. Fruit Growers' Assn. 1986. 

 92:106-109). To summarize, if the harvested fruit are low in Ca, they have a 

 reduced storage potential. Postharvest dips or drenches with calcium chloride 

 (CaCl2) can significantly improve fruit Ca levels and storage potential. 

 However, CaCl2 dips or drenches can cause spotting of fruit, usually seen as 

 small, black, sunken areas on the cheeks of the fruit or bronzing at the calyx 

 end, which may be serious enough to downgrade the fruit. Our earlier 

 recommendation of 21 lbs of CaCl2 per 100 gallons of water [ Fruit Notes 

 48(4): 18-19] was excessive and led to an unacceptable amount of spotting. More 

 recently we have suggested 12 lbs of CaCl2 per 100 gallons of water. This 

 amount is sufficient to significantly improve fruit Ca levels and potential 

 storage life, yet greatly reduces the risk of fruit spotting. 



During the past several years we have conducted a series of tests to try 

 to identify factors contributing to the amount of fruit spotting resulting from 

 postharvest CaCl2 treatments. Here we report the results of these tests. 



Time in solution : Most Ca that enters fruit from a conventional 

 postharvest treatment is taken in slowly over time from a residue. Thus, time 

 in solution is not a factor for Ca uptake as long as fruit are covered by 

 solution and a residue is established. In our tests we routinely dip fruit for 

 20 seconds for uniformity, but a shorter time would be sufficient; there is no 

 benefit from a longer period. There is some direct entry of solution into the 

 fruit through openings in the skin surface. These include the calyx canal, 

 lenticels, and wounds, even ones not visibly apparent. All of these entry 

 sites are variable among cultivars, handling practices, and growing conditions. 



Relative temperatures of fruit and water . Dips and drenches normally 

 employ cold water. However, fruit temperature can vary greatly. Our early 

 tests showed that the wanner the apple was at time of dipping, the more Ca it 

 absorbed. To determine the role of fruit temperature in spotting, we dipped 

 70°F Mcintosh and compared them with fruit first cooled to 320F. The solu- 

 tion was initially 50°F, but it either warmed or cooled during treatments, 

 depending on temperature of the apples. The warm fruit developed much more 

 spotting than did the cold fruit. The reason for this is probably that when a 

 warm fruit is plunged into cold water, the air inside the fruit quickly cools 

 and occupies less volume. This situation creates a partial vacuum that draws 

 solution into the apple through any openings in the fruit surface. Cells 

 around these openings are suddenly in contact with a high CaCl2 concentration 

 and they can be damaged, eventually dying and producing spots. Therefore, if 

 warm fruit are treated with a CaCl2 solution, a lower rate of CaCl2 may be 

 needed to avoid spotting. The better approach probably is to cool the fruit at 

 least partially before treatment or to ensure that the treating solution is at 

 a temperature fairly near that of the fruit. 



