SCALDING, PRECOOKING, AND CHILLING 9 
Both the physical and the chemical changes undergone by the 
chlorophyll of green leaves under various treatments have been 
thoroughly investigated by Willstatter and Stoll (56) , and the work 
of these writers throws much light upon the matter of retention or 
loss of the green color during canning operations. According to 
these authorities (55, p. 61), when the green leaves are heated in 
water, the chloroplasts become swollen and distorted, or may even 
burst, and the green color becomes more or less diffused throughout 
the cell. The spectrum analysis at this time shows only small 
differences from the pure chlorophyll extracted from the untreated 
leaves. In the fresh green leaves the chlorophyll is in a colloidal 
state, but when the temperature is raised by the scalding in hot 
water the chlorophyll passes into a true solution in the waxes within 
the cells. In any case, the changes which occur in the chlorophyll 
during the scalding occur also during the first few minutes of the 
processing, even in the material which has not been scalded. 
Chlorophyll is insoluble in water, and therefore does not leave 
the cells unless the cell walls are ruptured or destroyed. It is seen, 
therefore, that scalding does not bring the color to the surface of the 
green vegetables; and, since cooling merely hardens the cell waxes, 
plunging the freshly scalded vegetable into cold water does not 
bring about any changes in the chlorophyll which make it more 
resistant to chemical transformation by the heat of the subsequent 
sterilization process. This is in complete accord with the findings 
of the writers during the numerous experiments of the last four 
years, in which in no instance has it been possible to tell from the 
appearance and color of the finished product which material had 
been chilled in cold water and which had not. 
Willstatter and Stoll (55) have likewise shown that when chloro- 
phyll is heated in the presence of acids it is changed to phseophytin, 
a brownish compound. Vegetable tissues and juices are normally 
acid in reaction; and Masters and Garbutt (1^1), in their studies 
upon the losses incurred in the cooking of vegetables, noted that the 
water in which the vegetables were cooked, unless sodium bicarbonate 
had been added, was acid in reaction at the end of the experiment. 
As the above-named writers have already pointed out, the presence 
of these acids with their reaction upon the chlorophyll seems to ex- 
plain why the material which is bright green at the start becomes 
less attractive in color at the end of the cooking period. It also 
explains why the spinach or other vegetable which is bright green 
when it is put into the can or jar comes out of it at the end of the 
sterilization period with an olive-green or brownish green color. 
Copper salts form with chlorophyll a comparatively stable com- 
pound which gives to vegetables a deep-green color when these sub- 
stances are used in the scalding water. In some European countries 
copper salts have been quite commonly used to artificially color cer- 
tain canned vegetables, but owing to the poisonous nature of copper 
salts, their use for this purpose has been forbidden in this country. 
Several investigators (e. g., 41) have used sodium bicarbonate to 
preserve the green color of vegetables in cooking. The soda tends to 
hasten the cooking and to neutralize the acids which cause the de- 
composition of the chlorophyll. Experiments were performed to 
determine whether this could not be used to preserve the green color 
91941°— 24 2 
