Kinetic investigation into glucose-, fructose-, and sucrose-activated autoxidation of methyl linoleate emulsion |
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Authors: | Ahmed Fahmy Mabrouk L R Dugan Jr |
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Affiliation: | (1) American Meat Institute Foundation, The University of Chicago, Chicago, Illinois;(2) Present address: Northern Utilization Research and Development Division, Peoria, Illinois;(3) Present address: Department of Food Science, Michigan State University, East Lansing, Mich |
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Abstract: | Autoxidation of methyl linoleate emulsions in aqueous phosphate buffer solutions in the presence of glucose, fructose, and
sucrose has been studied by the rate of oxygen uptake. Oxidation rates increased with increasing concentration of sugars in
the system. At comparable molar ratios of sugar to methyl linoleate the rate of oxidation in the presence of fructose was
greater than with glucose which, in turn, was greater than with sucrose. Oxidation rates increased with pH until a maximum
rate was reached at pH 8.00. There was less conjugation and more CO2 with fructose than with glucose at a comparable level of oxygen uptake and pH value. This suggested concurrent oxidation
of methyl linoleate and sugars; fructose is the most readily oxidized of those studied.
Sugars seemed to be effective only in combination with the resulting methyl linoleate hydroperoxide. The effect of sugars
rests in an activation of the decomposition of the linoleate hydroperoxide, and on the acceleration of the autocatalysis.
The activation energy values for the autoxidation of methyl linoleate emulsions in the presence of sucrose, glucose, and fructose
are 14.9, 10.6, and 10.6 K. Cal./mol. at pH 5.50; 16.0, 10.8, and 10.4 K. Cal./mol. at pH 7.00; and 14.4, 10.2, and 8.8 K.
Cal. at pH 8.00, respectively.
Addition of ascorbic acid to the system at zero time or after 2 hrs. increased oxygen absorption. It appeared that oxidized
methyl linoleate caused co-oxidation of the ascorbic acid. Additions of nordihydroguaiaretic acid, propyl gallate, and hydroquinone
to the system were ineffective in stopping oxidation when they were added after oxidation had commenced. They reduced effectively
the rate of oxidation when added at zero time.
Presented at the 52nd annual meeting, American Oil Chemists' Society, St. Louis, Mo., May 1–3, 1961.
American Meat Institute Foundation Journal Paper No. 215. |
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