Induction period. There is a period before the uptake of oxygen by a fat
becomes appreciable which is known as the induction period. During this
period the fat is still fresh and "sweet." The induction period varies for
different fats and oils and for different samples of the same fat or oil. But
oxidation products act as catalysts so that oxygen uptake receives increased
momentum as these products are formed. Reports in the literature indicate
that the first compounds formed in oxidation of unsaturated fatty acids are
not oxides or peroxides. These compounds have never been isolated and
have been given the name "moloxides." Exclusion of air or oxygen from
a fat may retard but not inhibit its oxidation. It has been suggested that
the source of this oxygen is oxygen in loose combination with the fat. It is
sometimes suggested that loosely bound oxygen is the source of oxygen
for the moloxides.
Prooxidants and antioxidants. A prooxidant accelerates but an antioxi-
dant retards oxidation of a fat. Because of the economical importance of
prevention of rancidity many investigations have been conducted to find
physiologically harmless antioxidants. The literature on rancidity is volumi-
nous and many contradictions occur, particularly in regard to the activity
of different substances as accelerators or retarders of oxidation. The con-
tradictions can be attributed to the lack of suitable tests for minute quanti-
ties of some substances, the different conditions under which the tests are
made, and the differences in degree of purity or refinement of the fats and
oils. Fats and oils always contain at least traces of different substances in
varying proportions, some of which can act as prooxidants and others as
antioxidants. Patents have been granted for the use of many substances
as antioxidants.
Metals. Traces of certain metals (King, Roschem, and Irwin) may act
as catalysts, copper in particular being an active prooxidant. Tin had the
least effect of any metals used in the experiments, although the authors
state the results were not conclusive in that tests were not made under many
552 FATS AND OILS
conditions. The effect of metals is important, for in the manufacture, re-
fining, and storage of fats they come in contact with metals.
Lecithin. Lecithin, found in egg yolk, soybeans, and other substances
added to baked products, has been reported to be a powerful antioxidant
and inactive. Olcott and Mattill say that commercial "lecithin," which is
not a pure lecithin, has antioxidant action on refined cottonseed oil, little
effect on lard, and none at all on lard-cod liver oil mixtures. They
attribute the antioxidant properties to the cephalin found in the commercial
lecithin. It is well known that egg yolk has antioxidant properties in
cookies, cakes, and similar products in which both egg yolk and fat are
used.
Cereals. Soybean flour (Musher) is said to be strongly antioxidant. Oat,
corn, barley, or other cereal may be employed but oat flour is preferable
because of its bland flavor. Wheat flour is a weak retarder of oxidation
and oat flour is not as strong an antioxidant as soybean flour.
Page 438
Presented as published in 1932. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
A modernized reading is not available for this page yet. You are seeing the original text.
Induction period. There is a period before the uptake of oxygen by a fat
becomes appreciable which is known as the induction period. During this
period the fat is still fresh and "sweet." The induction period varies for
different fats and oils and for different samples of the same fat or oil. But
oxidation products act as catalysts so that oxygen uptake receives increased
momentum as these products are formed. Reports in the literature indicate
that the first compounds formed in oxidation of unsaturated fatty acids are
not oxides or peroxides. These compounds have never been isolated and
have been given the name "moloxides." Exclusion of air or oxygen from
a fat may retard but not inhibit its oxidation. It has been suggested that
the source of this oxygen is oxygen in loose combination with the fat. It is
sometimes suggested that loosely bound oxygen is the source of oxygen
for the moloxides.
Prooxidants and antioxidants. A prooxidant accelerates but an antioxi-
dant retards oxidation of a fat. Because of the economical importance of
prevention of rancidity many investigations have been conducted to find
physiologically harmless antioxidants. The literature on rancidity is volumi-
nous and many contradictions occur, particularly in regard to the activity
of different substances as accelerators or retarders of oxidation. The con-
tradictions can be attributed to the lack of suitable tests for minute quanti-
ties of some substances, the different conditions under which the tests are
made, and the differences in degree of purity or refinement of the fats and
oils. Fats and oils always contain at least traces of different substances in
varying proportions, some of which can act as prooxidants and others as
antioxidants. Patents have been granted for the use of many substances
as antioxidants.
Metals. Traces of certain metals (King, Roschem, and Irwin) may act
as catalysts, copper in particular being an active prooxidant. Tin had the
least effect of any metals used in the experiments, although the authors
state the results were not conclusive in that tests were not made under many
552 FATS AND OILS
conditions. The effect of metals is important, for in the manufacture, re-
fining, and storage of fats they come in contact with metals.
Lecithin. Lecithin, found in egg yolk, soybeans, and other substances
added to baked products, has been reported to be a powerful antioxidant
and inactive. Olcott and Mattill say that commercial "lecithin," which is
not a pure lecithin, has antioxidant action on refined cottonseed oil, little
effect on lard, and none at all on lard-cod liver oil mixtures. They
attribute the antioxidant properties to the cephalin found in the commercial
lecithin. It is well known that egg yolk has antioxidant properties in
cookies, cakes, and similar products in which both egg yolk and fat are
used.
Cereals. Soybean flour (Musher) is said to be strongly antioxidant. Oat,
corn, barley, or other cereal may be employed but oat flour is preferable
because of its bland flavor. Wheat flour is a weak retarder of oxidation
and oat flour is not as strong an antioxidant as soybean flour.