Abstract
Since some of the phosphate esters derived by hydrolysis of Phosphatides have been found to show antioxidant activities in the dry unsaturated fatty acid esters, the authors examined whether they as well as some trialkyl esters of phosphoric acid show the activities in the water-unsaturated fatty acid ester system. Two techniques were employed : (1) Analytical grade filter paper was used for even distribution of the reactants, and increase in peroxide value (expressed as m mole of oxygen/100g substrate) with time was determined for examination of effects on pH. (2) The Warburg apparatus was employed for examination of optimum concentrations (in a range from 0.01 to 0.1%) for the phosphate esters at pH 7.8.
In the case of 0.0006mM solution all the esters examined showed prooxidant activities instead of antioxidant at pH 4.0. On the other hand, at pH 5.5, glycerylphosphorylserine showed the strongest activity, followed by phosphorylcholine (PC). Glycerylphosphorylcholine (GPC) showed the activity comparable to that of glycerylphosphoric acid (GP), which is generally active in various fatty acid esters, whereas phosphorylethanolamine (PE) and glycerylphosphorylethanolamine (GPE) exhibited no antioxidant activity. At pH 0.6 the GPC was found to be strongly active among others such as PE, PC and β-GP. Contrary to the findings in the dry fatty acid ester system (unpublished work), the trimethyl and triethyl phosphates showed an antioxidant activity at pH 5.5, while tributyl phosphate was less strongly active. These results as well as those obtained in the alkaline pH probably indicate that the P=O and P-O- groups in the phosphates are also related to the antioxidant activity in addition to the P-OH groups as was formerly suggested.
The following percentages may be taken as possible optimum concentrations in the water-methyl linoleate system; PG 0.03% or less in fresh or somewhat oxidized substrate, PE 0.03-0.04% in fresh, PC 0.03% in fresh, PGE 0.04% in fresh, and GPC 0.03-0.05% in either fresh or somewhat oxidized substrate.
