POPULAR SCIENCE 617 



of preserves (e.g. jam), and here the questions of appearance 

 and consistency are unimportant, and it is rather properties 

 such as aroma and power of gelatinisation to which attention 

 must be principally directed. 



It must be strongly emphasised that the value of each 

 species or even variety of fruit depends upon something very 

 specific in the matter of aroma and flavour. On this account 

 each species will have to form the subject of a separate investi- 

 gation, largely biochemical, in order to determine the best 

 conditions of storage. 



We shall first consider the chemical changes undergone by 

 fruits in general during ripening. These changes relate to 

 two classes of substances : carbohydrates and organic acids. 

 As regards carbohydrates the unripe fruit contains starch, 

 disaccharides (chiefly cane sugar), and monosaccharides (glu- 

 cose, fructose), as well as the cellulose of the cell walls, and 

 degradation products of starch such as dextrin. In the first 

 stage of the ripening process the starch decreases in quantity, 

 and ultimately disappears, being hydrolysed to sugars, 1 which 

 thus correspondingly increase. This decrease in starch content 

 runs parallel with the softening of the fruit, but is not the 

 only cause of it. The second stage of ripening is marked by 

 the inversion of cane sugar into glucose and fructose, and this 

 diminution of cane sugar and increase in hexoses continues 

 until the fruit commences to rot. Throughout the whole of 

 the ripening period respiration is proceeding by which the 

 sugars are transformed to carbon dioxide. While the trans- 

 formation of starch to sugar is characteristic of one phase of 

 ripening, and the inversion of cane sugar of the second stage, 

 respiration takes place in the earliest stages of ripening and 

 continues over the whole period. It involves, of course, a loss 

 of valuable material. 



It was earlier assumed that the acid content of fruit did 

 not undergo any significant alteration during ripening, and it 

 was supposed that improvement in taste was due to increase 

 in sugar content. It is now realised, however, that the acid 

 content decreases continually during ripening, and that this 

 causes the fruit to taste sweeter. The acid content must not 

 sink too low as otherwise the taste deteriorates, the best flavour 



1 Bigelow, Gore, and Howard, " Studies on Apples," U.S. Department of 

 Agriculture, Bureau of Chemistry, Bull. 94, 1905. 



