VEGETABLE PROTEIDS. 155 



VEGETABLES, 



The green vegetables form a very important part of the food 

 of man. It is true that they contain a large amount of water, 

 varying from 75 to 95 per cent. ; still, they also contain carbo- 

 hydrates, and are one of the principal sources from which these 

 food-stuffs are derived. Thus in potatoes, while there is but 2 

 per cent, of proteids, and only 0.2 per cent, of fat, there is 20 per 

 cent, of starch. The pulses or leguminous plants, such as peas, 

 beans, and lentils, supply man in their seeds with food which is 

 rich in proteids as well as in carbohydrates ; thus in peas there are 



23.7 per cent, of proteid and 49.3 per cent, of starch ; in lentils, 



24.8 per cent, of proteid and 54.8 per cent, of starch. The pro- 

 teids of the pulses are of the nature of vitellin and globulin. In 

 the kidney-bean two globulins, phaseolin and phaselin, besides 

 proteose have been found. 



Vegetable Proteids. The proteids in vegetables may exist 

 in three forms: (1) In solution in the juices of the plant; (2) in 

 the protoplasm ; or (3) in aleurone grains. They are classified, as 

 are the animal proteids, into albumins, globulins, albuminates, pro- 

 teoses and peptones, and coagulated proteids. What was formerly 

 spoken of as legumin or vegetable casein, or simply vegetable 

 proteid, is now held to be an alkali-albumin produced by the 

 action of the alkali used in the extraction on the globulins which 

 exist normally in the plant. Proteoses have been found in the 

 various varieties of flour, as well as in the circulating fluids of 

 plants, and in the latter also occur hemi-albumose, leucin, tyrosin, 

 and asparagin. Enzymes also exist in plants, and to those of a 

 proteolytic character these proteoses are probably due. Some 

 of these proteolytic enzymes have been carefully investigated, 

 notably papain in the papaw plant, and bromelin in pineapple- 

 juice. In the juice of the papaw are a number of proteids : a 

 globulin resembling serum-globulin, an albumin, and two pro- 

 teoses, with one of which papain is associated. This enzyme is 

 very much like trypsin. 



Bromelin acts in neutral, acid, or alkaline media, acting particu- 

 larly well at 60 C. It produces proteoses and peptones, and 

 is used to prepare artificially digested foods. 



Enzymes are very abundant in the vegetable kingdom, and 

 have for their office the conversion of the insoluble proteid of the 

 seed into the soluble nitrogenous substances of the sap. They 

 are, however, not all of a proteolytic nature. There are also those 

 that are amylolytic, as the diastase in barley, and these enzymes 

 change the starch of seeds into sugar. Such a conversion we have 

 already referred to in the process of bread-making when the wheat- 

 starch first becomes sugar, and then undergoes alcoholic fermenta- 

 tion under the influence of yeast. 



