TRACE METALS IN FOODS 3 



derived from a single sample or a small group has little significance. For those 

 desiring comparable data on the fresh product, the factors .05, .10, .15, and .20 

 may be applied to the results published for materials containmg 95, 90, 85, and 

 80 percent of moisture. 



Classification of Food Products 



For comparative purposes the samples have been grouped according to the 

 nature of the product and its use as a food. The determination of the proximate 

 constituents was a secondary objective but serves to show to what extent sub- 

 stitution may be feasible. The following classification was employed. The 

 botanical classification used is that of Albert F. Hill.i 



Major Fruits — large fruits such as apples and peaches 



Minor Fruits— berries 



Vegetables 



Garden Fruits — pumpkins, squash, melons, etc. 

 String Beans 

 Peas and Shell Beans 



Leaf and Stem — spinach, lettuce, celery, cabbage, onions, etc. 

 Root — beet, turnip, radish, carrot, potato, etc. 

 Cereals, low fiber — without hulls or with hulls removed 

 Cereals, high fiber — with hulls, as oats 

 Nuts 



Processed Human Foods — breakfast foods 

 Cattle Feeds, low protein 

 Cattle Feeds, medium to high protein 

 Roughage 



Kitchen Waste — fruits and vegetables 

 Miscellaneous 

 With the elimination of water, most natural and processed foods contain 

 from 50 to 90 percent or more of soluble or easily digested carbohydrates (sugars 

 and starch). Exception will be noted later. Appreciable amounts of protein 

 occur in some members of most groups. Fat is a minor constituent except in 

 one group. Fiber is present in nearly all plant foods and tends to increase in 

 most instances with maturity and overripe stages of growth. 



The soluble ash constituents of natural foods vary with environmental condi- 

 tions and feeding ability of the plant. The insoluble ash (largely silica) is due 

 frequently to the retention of soil particles in the interstices of the leaves. When 

 the amount exceeds 0.50 percent, the determination of trace metals may be 

 vitiated. 



Metliods Employed 



The following analytical methods were employed: moisture was determined 

 by drying in a vacuum oven at 50° C to constant weight; protein (N x 6.25), 

 by the Kjeldahl-Gunning method with salicylic acid; fat, by extraction with 

 anhydrous ethyl ether; fiber, by the Official Method for Grain and Stock Feeds^; 

 and ash, by incineration in an electric mufifle below visible redness (about 500'^ C). 

 By acid extraction, the crude ash was resolved into two carbon-free portions, 

 soluble and insoluble. 



'Economic Botany. 1st Ed. 592 pp. McGraw-Hill Book Company. 1937. 

 'A. O. A. C. Methods of Analysis, 4th Ed. pp. 340-341. 1935. 



