Role of the bases and phosphoryl bases of phospholipids in the autoxidation of methyl linoleate emulsions |
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Authors: | Lee-Shin Tsai Lloyd M Smith |
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Affiliation: | (1) Department of Food Science and Technology, University of California, 95616 Davis, California |
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Abstract: | Methyl linoleate, emulsified in borate buffer with sodium lauryl sulfate, was used to study the pro- or antioxidant effect
of 0-phosphocholine, 0-phosphoethanolamine, 0-phosphoserine, as well as the corresponding nonphosphoryl compounds. Oxygen
uptake was calculated from rate data obtained at 37 C with an oxygen electrode. The results were similar for the corresponding
phosphoryl and nonphosphoryl bases. 0-Phosphocholine and choline had little effect at either pH 7.9 or 10.2. 0-Phosphoethanolamine
and ethanolamine significantly increased oxygen uptake at pH 7.9, but significantly decreased uptake at pH 10.2. 0-Phosphoserine
and serine decreased oxygen uptake at both pH values. The catalytic activities of the bases investigated may be attributed
to their functional groups. The phosphoryl and β-hydroxy groups exhibited no catalytic activity in the autoxidation of methyl
linoleate emulsions at either pH 7.9 or 10.2. The α-carboxyl amino group of 0-phosphoserine and serine decelerated autoxidation
at both pH values. The amino group H3N+ of the primary amine accelerated autoxidation, but the H2N: group and the reverse effect. Since the quaternary amino group (CH3)3N+ did not affect autoxidation at either pH 7.9 or 10.2, we concluded that the presence of the N−H bond may be necessary for
the prooxidant activity of an amine, and that the presence of a pair of free electrons on the nitrogen of an amine is necessary
for its antioxidant activity. Kinetically, the autoxidation of methyl linoleate emulsion without added base was in agreement
with Farmer’s proposed mechanism involving a bimolecular dissociation of hydroperoxides. However, methyl linoleate emulsion
at pH 7.9 and 37 C in the presence of ethanolamine or 0-phosphoethanolamine was autoxidized by a mechanism involving a combined
mono- and bimolecular dissociation of hydroperoxides.
Submitted as partial requirement for a Ph.D. degree in Agricultural Chemistry. Presented in part at the AOCS Meeting, San
Francisco, April 1969. |
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