TRAcfE METALS AND TOTAL NUTRIENTS 



IN HUMAN AND CATTLE FOODS 



By E. B. Holland, Research Professor, and W. S. Ritchie, Professor of 



Chemistry 



Foods have been a subject for investigation by the Massachusetts Experiment 

 Station ever since its organization, and comprise a wide range of products. Re- 

 cently the determination of trace metals, supposed to have a functional activity 

 in assimilation and possibly some therapeutic value, has received major atten- 

 tion. As natural food products are in themselves responsive in assimilation and 

 growth to seasonal, cultural, and other environmental conditions, the problem 

 becomes somewhat involved. 



Collection and Preparation of Samples 



Numerous samples of fruits and vegetables were obtained from the State Col- 

 lege and vicinity and many vegetables from the Waltham Field Station and east- 

 ern market gardeners. Similar samples were secured from other sections and in 

 addition cereals, nuts, processed human foods, and cattle feeds. Duplicates in 

 succeeding years served to check variability in some measure. All samples were 

 expected to be mature, marketable products in prime condition for use, but some 

 failed to meet these requirements. Immature and overripe products vary appre- 

 ciably in proximate constituents but to a less extent in trace metals. The type 

 and rapidity of growth are also factors influencing composition. Respiratory 

 changes in some fruits and vegetables during transportation and storage affect 

 composition at the expense of the carbohydrates. 



The samples were culled as in household practice, washed if necessary, com- 

 minuted, and dried in an electrically heated oven in a strong current of warm air 

 (about 50° C). Under such treatment the tissue sets quickly with a minimum of 

 deterioration in fat and carbohydrates. Many of the early samples were pared 

 or scraped but the practice was largely discontinued later. The dried samples 

 were ground to a 1 mm. sieve and preserved in glass containers for subsequent 

 analysis. 



Basis of Analysis 



Most fruits and vegetables contain from 80 to 96 percent of water at maturity 

 but lose rapidly on exposure. These foods are frequently marketed fresh, frozen, 

 canned, or dried. On the other hand, most cereal products, navy beans, nuts, 

 oil meals, and other industrial by-products are substantially air-dry when market- 

 ed. With such a range in moisture content, dry matter offers the most equitable 

 basis for comparison. Pro.ximate constituents are reported in percentage and 

 trace metals in parts per million. 



As previously stated, most fruits and vegetables are high in moisture when 

 received by the consumer in fresh condition but lose water on exposure in harvest- 

 ing and in transportation and storage. The amount of loss will, of course, vary 

 with the character of the product and subsequent treatment. Generally the 

 dry matter will range from 5 to 20 percent. Comparatively few contain less than 

 5 percent, but others having a long ripening period or suffering undue e.xposure 

 will contain more than 20 percent of dry matter. Any arbitrary percentage 



