rooms were swabbed with dry cotton balls that had been 

 pre-rinsed in hexane. The swabs were then extracted in 

 hexane, which was monitored for DPA. All samplings 

 produced DPA residues on storage surfaces, ranging 

 from 0.4 to 13.1 ug/meter^ of surface. Thus, DPA in 

 apple peel could have been the result of contamination 

 from residues in the storage. 



To eliminate this possibility, 10-fruit samples of 

 fruit were taken direcdy from trees at the HRC in 

 August, 1993 while fruit were immature. The same four 

 cultivars tested out of storage were sampled from the 

 trees, and also fruit were taken from an organically- 

 grown treeof Rhode Island Greening. Fruit again were 

 sampled from these trees when they were mature. In 

 addition, Mcintosh were sampled again when they were 

 ovenmature, and Anjou pears were sampled at maturity. 

 All of these samples were extracted in hexane immedi- 

 ately after harvest, and the extracts were frozen until 

 analysis. All samples exhibited the presence of DPA 

 (Table 2), although the concentrations were about one- 

 tenth those found in stored fruit. It is interesting to note 

 the increase in fruit weight between the two harvests, 

 without a reduction in DPA concentration, which indi- 

 cates that the material continued to accumulate as the 

 fruit grew. 



These results strongly supported the suggestion 

 that DPA is a natural product in apples... and also in 

 pears. However, for additional confirmation, two more 

 tests were run. First, a Mcintosh extract was spiked 



with a minute amount of authentic DPA to make sure 

 the method was recovering and measuring DPA. Spik- 

 ing doubled the DPA measurement, with a 61% recov- 

 ery of added DPA, so the procedure is capable of 

 extracting and measuring DPA. 



A more rigorous evaluation of the procedure was 

 made by producing a derivative of DPA, i.e., attaching 

 another molecule to it, and separating and measuring 

 the deri vatized molecule. This procedure is a test to see 

 if it is truly DPA that was being measured. 

 Derivatization produced three different ions; DPA plus 

 the derivatizing substance, DPA plus part of the 

 derivatizing substance, and DPA with a single proton 

 removed from it. Using authentic DPA, these ions were 

 in a ratio of about 1.0:0.6:0.3. When fruit extracts were 

 derivatized, the three ions were not present in that ratio, 

 raising doubts that we truly were measuring DPA. 



To test this further, 10-fruit samples of Delicious 

 apples, from the same tree, that had and had not been 

 dipped in DPA before storage were taken from storage 

 in March, extracted, derivatized, and measured. The 

 DPA-treated fruit contained 10 times as much 

 derivatized DPA as did the non-u-eated fruit, and in the 

 treated fruit the ion ratio was 1 .0:0.6:0.3, indicating that 

 it was DPA that was being measured. In the non-treated 

 fruit, the ratio was about 1.0:0.3:0.2, just as we found in 

 the freshly harvested fruit. 



That result reaffirmed that at least part of what we 

 were measuring as "DPA" in apple extracts probably 



Fru'n Notes, Fall, 1994 



13 



