Enzyms of Apples 105 



I 



in about four weeks were visibly overripe, the lower ones beginning to 

 collapse under the pressure of the weight of the upper layers. Those in 

 oxygen seemed to ripen a little more rapidly, but the difference was not 

 nearly so great as had been expected and was hardly enough to warrant 

 any conclusion that pure oxygen hastened the ripening process. Those 

 which were surrounded by nitrogen and hydrogen did not soften so 

 noticeably, but became discolored and unhealthy in appearance, a phe- 

 nomenon later observed and reported by Hill (8).^ After some 8 or 10 

 weeks, however, these apples also softened into a mushy mass. The 

 apples in carbon dioxid and in sulphur dioxid remained apparently firm 

 and unchanged for a long time, except that the latter gas completely 

 bleached the skins of the apples in its jar, leaving them a uniform creamy 

 white in color. After nearly six months had elapsed, these jars were 

 opened and the fruit examined. That which had been in an atmosphere 

 of sulphur dioxid was firm and soUd, but was, of course, so thoroughly 

 impregnated with the disagreeable gas that its quaHty could not be 

 judged. The apples which had been in carbon dioxid were firm in flesh, 

 possessed the characteristic apple odor, although the gas in the jar had a 

 slight odor of fermented apple juice, and were not noticeably injured in 

 flavor. 



It appeared, therefore, that the phenomena ordinarily associated with 

 ripening were greatly inhibited by an atmosphere of carbon dioxid, but 

 that the cause of this inhibition was not wholly a lack of oxygen. It 

 seemed that the changes taking place in the apple were not simple 

 respiratory changes, but probably in large part were internal enzymic 

 activities. 



The experiment was repeated the following summer, using raspberries, 

 blackberries, and loganberries instead of apples. It was found that 

 berries which softened in 3 days in air would remain firm for from 

 7 to 10 days in an atmosphere of carbon dioxid. At this point the 

 studies were interrupted by a change in professional engagements and 

 have not been resumed. 



Recently, Hill (8) reported a series of observations so similar in charac- 

 ter that interest in the matter was revived; and opportunity being pre- 

 sented for a systematic study of the enzyms of apples by a graduate 

 student^ working under the writer's direction, such a study was under- 

 taken, with the results reported below. 



CHANGES IN CHEMICAL COMPOSITION OF APPLES DURING RIPENING 



The changes in the chemical composition of apples during ripening 

 have been very thoroughly studied by Bigelow, Gore, and Howard (2). 

 The report of their investigations contains a careful review of the liter- 

 ature on the subject, together with significant contributions from the 



' Reference is made by number to " Literature cited." p. ii6. 



- The writer's thanks are due to Miss Inez Everett, the graduate student who assisted in the preparation 

 of the material for examination and the carrying out of the several tests. 



