460 MICROBIOLOGY OF SPECIAL INDUSTRIES 



time, the object being, first, to remove the mucous substance from the 

 outside and a part of the green coloring matter so as to have a clear 

 liquor in the can, and second, to drive water into the vegetables so that 

 all will be tender. The blanching process also improves the color of 

 these vegetables. 



Mechanical Disinkgratton.-^ln the case of very soft fruits or vege- 

 tables, the high temperature essential for sterilization causes a slight 

 amount of mechanical disintegration, which is not objectionable, how- 

 ever, unless excessive, as there is Httle deterioration in appearance, and 

 none in food value. In the case of meats, practically the only physical 

 change is the shrinkage during the parboUing previous to placing in 

 the cans. 



Chemical Changes. — Appearance. — ^The chemical changes in foods 

 preserved by heat may be considered under two heads: first, those in 

 which the appearance is modified; and second, those in which the food 

 itself is altered. Some change of color sometimes occurs and results 

 from various causes. In colored vegetables, such as peas, string beans, 

 and asparagus, a part at least of the loss of color is due to the oxidation 

 of chlorophyll. With a few foods, iron sulphides are occasionally 

 formed by a combination of sulphur of the foods with the iron of the 

 container. This seldom occurs however, and is not of great impor- 

 tance. Some fruits packed in glass gradually lose their color by oxida- 

 tion on exposure to the light. 



Chemical Change. — So far as chemical alteration of the food itself 

 is concerned, there is little change and none other than would occur in 

 the ordinary preparation of the food for the table. The albumins are 

 coagulated. The fats probably remain unchanged. Of the carbo- 

 hydrates, the chief action is on the sugars. The cane sugar is wholly 

 or partly inverted by the combined action of the heat and the fruit or 

 vegetable acids. The starch undergoes little if any cleavage, inasmuch 

 as this change occurs only in the presence of acids, and in foods with a 

 high acid content, the proportion of starch is relatively low. The other 

 amyloses probably undergo little if any change. 



Palatability and Digestibility. — It is often contended that canned 

 foods are less palatable than fresh foods of the same kind. This lack 

 of agreeableness to the taste is, however, more seeming than real, and 

 arises largely from the prejudice of the consumer against food conserved 

 in tin cans, rather than from any actual change. When the preserving 



