Effect of water activity on secondary products formation in autoxidizing methyl linoleate |
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Authors: | A G Gopala Krishna J V Prabhakar |
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Affiliation: | (1) Discipline of Confectionery & Convenience Foods, Central Food Technological Research Institute, 570013 Mysore, India |
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Abstract: | The role of water activity on the formation of peroxides and carbonyl compounds during lipid oxidation is important to know
because there could be either beneficial or detrimental effects of water activity on lipid oxidation in stored foods. Therefore,
methyl linoleate was chosen as a model lipid and was autoxidized to 1% at water activity ranging from 0.02 to 0.79 at 37°C.
Oxygen uptake was monitored manometrically. The peroxide and carbonyl contents were determined upon termination of the autoxidation
studies. Methyl linoleate autoxidation was characterized by three phases: i) an initial induction period of no oxygen absorption;
ii) a slow rate of oxygen absorption, up to 0.15% oxidation; and iii) a relatively faster rate of oxygen absorption beyond
0.15% up to 1% oxidation. Water activity had considerable influence during the first phase. There was no induction period
at or below water activity 0.22. The induction period begins at water activity 0.32 and could be extended to a limit with
increase in water activity. Once the induction period was passed water activity had no influence on the rate of oxidation.
However, during the second and third phases water activity becomes important in the stabilization of peroxides/hydroperoxides
and decides the course of secondary reactions that follow peroxide decomposition. Higher water activity values, particularly
water activity 0.67, tended to stabilize peroxides. Water activity had considerable influence on the formation of secondary
products of autoxidation as evidenced by the variation in the type and quantity of carbonyl compounds at different water activity
values. |
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Keywords: | Autoxidation carbonyl compounds methyl linoleate peroxides secondary products of autoxidation water activity |
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