TOTAL ACIDITY 



In ml. N/10 NaOH 



T r 



- yZ£ 



Rome Beauty^ ,, *V 



Golden Delicious 



1 - I 



40 

 20 



- 



' ?: 



*»•... rjr.nr. 



U.S. DEPARTMENT OF AGRICULTURE 



6 3 6 



MONTHS 



* 'STORAGE e TESTED IN FIRST YEAR ONLY 



NEG 5578-58(10) AGRICULTURAL RESEARCH SERVICE 



Figure 3. — Total acidity of six varieties of mature apples before and after 

 storage at 32° and 40° F., mean values for 2 crop years combined. 



PH 



Among the mature apples, freshly harvested Stayman apples were 

 the most acid with a pH of 3.3 and Delicious apples were the least 

 acid with a pH of 4.1. These two varieties also were highest and 

 lowest, respectively, in total acidity. The other varieties did not 

 differ greatly in pH, although in total acidity they varied considerably. 

 For example, Rome Beauty and Jonathan had about the same pH, 

 3.5 and 3.4, although Jonathan had a much higher total acidity than 

 Rome Beauty. 



Immature apples when freshly harvested had approximately the 

 same pH values as the corresponding varieties of mature apples and 

 increased in pH during storage to about the same extent as mature 

 apples. It was shown previously that changes in total acidity of 

 immature apples in this study were similar to those in mature apples. 



After storage for 7 months at 32° or 40° F., pH values increased 

 in all varieties, but increased less in those with high total acidity. 

 Delicious, Golden Delicious, and Rome Beauty varieties in the group 

 low in total acidity, after storage had the highest pH values and were 

 the only mature varieties with values above pH 4.0. The changes 

 in pH were similar for apples stored at either temperature. Wright 

 and Whiteman (54) reported comparable increases in pH from 3.86 to 

 4.17 in Delicious apples during 7 months of storage, and from 3.46 to 

 3.55 in Stayman apples during 6 months of storage. 



The coefficient of correlation between pH and total acidity of mature 

 apples in this experiment was —0.85. This correlation is highly 

 significant and indicates that 72 percent of the variation in pH is 

 associated with the total acidity of the apples. Barnes (8), in a 

 study on 33 varieties of Minnesota apples, reported a coefficient of 

 correlation of —0.93 between pH and titratable acidity. 



498308 O— 59- 



29 



