Is Diphenylamine a Natural 

 Compound in Apples and Pears? 



William J. Bramlage and Zhigao Ju 



Department of Plant & Soil Sciences, University of Massachusetts 



Thomas L. Potter 



Mass Spectrometry Facility, University of Massachusetts 



For over 30 years, dipping fruit in diphenylamine 

 (DP A) before storage has been the standard commercial 

 procedure to control superficial scald (scald) develop- 

 ment on apples during and after long-term storage. 

 However, this procedure is controversial since it consti- 

 tutes a chemical treatment, and legally, DPA must be 

 considered as a food additive. Some countries have 

 banned treatment with DPA, and some prohibit impor- 

 tation of DPA- 



treated fruit. In the U.S. and Canada, DPA is permitted 

 and the maximum residue of 10 ppm should never be 

 exceeded if DPA is applied correctly. Nevertheless, 

 many American markets will not accept DPA-treated 

 fruit because they have been chemically treated. 



In 1984, a report was published (Karawya and 

 Wahab.y.Afamra/ProducW 47(5): 775-780) that DPA 

 was found in relatively high concentrations as a natural 

 product in mature onions, and that it was effective in 

 lowering blood sugar levels in diabetics. 

 The report also showed data that DPA was 

 a natural product in tea. In that same year, 

 a report of the Food and Agriculture Orga- 

 nization of the United Nations ("Pesticide 

 Residues in Food - 1984") stated that there 

 "...is reasonable evidence that dipheny- 

 lamine occurs naturally in apples though 

 the level appears to be at or below 1 mg/kg 

 (ppm)." No data to support this statement 

 were cited, but in studies of DPA residues 

 on apples, controls almost always contain 

 measurable amounts of DPA. 



We became interested in this question 

 when what appeared to be DPA was de- 

 tectable, even though no DPA had been 

 applied, during our measurements of ma- 

 terials in apple peel that might be associ- 



ated with scald development. In 1993, the Massachu- 

 setts Fruit Growers' Association provided us with a 

 grant to pursue this question, and results of our study are 

 reported here. 



In April, 1993 10-fruit samples were taken fiom 

 bins of apples stored at the University of Massachusetts 

 Horticulture Research Center (HRC), Belchertown. 

 Five cullivars were sampled, and fruit were extracted in 

 hexane. The extract was tested for presence of DPA 

 using gas chromatography and mass spectroscopy, 

 employing selected-ion-monitoring for maximum sen- 

 sitivity. Results are shown in Table 1. All samples gave 

 positive indication of DPA in their peel, ranging from 

 0.03 to 0.13 ppm, despite the fact that none had been 

 treated with DPA after harvest. 



DPA is somewhat volatile, so to test for the pres- 

 ence of DPA residues in the rooms at the HRC, one- 

 square-foot areas of walls and doors in three different 



12 



FruH Notes, Fall, 1994 



