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Massachusetts
agricultural experiment station

Bulletin No. 379 July. 1941



Trace Metals and Total Nutrients
in Human and Cattle Foods

By E. B. Holland and W. S. Ritchie



This information concerning the composition of various plant materials is
p/ovided because of the very general interest in the nutritional function of certain
trace elements.



MASSACHUSETTS STATE COLLEGE
AMHERST, MASS.



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



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.



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Online LibraryMassachusetts Agricultural Experiment StationBulletin - Massachusetts Agricultural Experiment Station (Volume no.379-398) → online text (page 1 of 77)