CHFlalCAL AND PHYSICAL CHANGES IN APPLES DURING STORAGE 



The function of cold storages is well kno-vm to the fruit grower. It 

 is knaun that apples must be stored if the fruit is to be kept in good 

 sa^ble condition during the winter and spring months which is to the mutual 

 benefit of both the grower and consumer, Viihat is less well known to the 

 fruit grower is the chemical and physical changes in the apples during 

 storage. 



First it must be realized that the apple is alive even though it has 

 been picked from the tree. Apples continually carry on respiration iirhich 

 consists of the intake of oxygen and the giving - off of carbon dioxide 

 through the skin, other words they breathe. In addition to the carbon 

 dioxide, water vapor, volatile substances and heat also are given off as 

 products. The rate the breathing or respiration depends on the temperature 

 at which they are stored ••-■At ordinary room temperatures, apple respire 

 much more rapidly than at storage temperatures of 31° to 32° F, The 

 faster an apple respires, the faster it ripens, 



1/Yhat else takes place in the ripening process of apples during storage? 

 Infhen an apple is harvested its tissue consists largely of water and such 

 carbohydrates as sugars in the form of sucrose and reducing sugars, fruit 

 acids, and i' betvreen the cell walls, cellulose like substances (proto- 

 pectin and pectates) from which pectins are produced, Pectiia is found 

 only in low concentrations at the tiiiie the apple is picked. 



After the apple is removed from the tree a series of complex chemical 

 changes take place. Starch is converted to sugar j rate of respiration 

 increases] ethylene and other gases are evolved^ changes take place in 

 fruit color; svigars change formj acids decrease; and protopectin is 

 converted to pectin. 



During storage there is a continued change from green color to yellow 

 color on the unblushed side of the fruit, "while the red color of apples 

 may increase at room temperature after picking, there is no increase after 

 the fruit has been placed in storage. 



At the time the apple is at commercial maturity, it contains alot of 

 protopectin and pectin and an appreciable amount of pectate. These pectic 

 substances cement the cells together and this adhesion is responsible for 

 the firmness and crispness of the apple flesh. As the fruit continues to 

 ripen, the pectic substances are lost at a progressively increasing rate, 

 liYith the dissolution of the pectate between the cell walls, the cells of the 

 overripe fruit become loosened or even completely freed from one another, 

 and the fruit becomes soft and mealy, Siniiar changes take place during 

 the ripening of the pear and peach. 



In a recent Technical Bulletin published by the Unites States Depart- 

 ment of Agriculture, it was found that reducing sugars tended to increase 

 during storage while sucrose increased only during the first 1 or 2 months 

 in the apple varieties tested. Total sugar increased while acidity decreased 

 during storage. 



