British Journal of Nutrition

Papers on General Nutrition

Reactions of proteins with oxidizing lipids

1. Analytical measurements of lipid oxidation and of amino acid losses in a whey protein-methyl linolenate model system

Henrik K. Nlelsena1 p1, J. Löligera1 and R. F. Hurrella1

a1 Research Department, Nestlé Products Technical Assistance Co. Ltd, CH-1814 La Tour-de-Peilz, Switzerland

Abstract

1. The reactions between protein-bound amino acids and oxidizing lipid were investigated in a whey protein-methyl linolenate (C18.3)–water model system. The extent of fat oxidation was followed by measuring oxygen uptake, hydroperoxide formation and hydrocarbon (ethane and pentane) formation.

2. Significant losses occurred with lysine (up to 71 %), tryptophan (up to 31 %) and histidine (up to 57%). Methionine was extensively oxidized to its sulphoxide but less than 2% was further oxidized to the sulphone. No other amino acids were affected.

3. Increasing storage temperature (20°, 37°, 55°) resulted in an enhancement of fat oxidation reactions and amino acid degradation.

4. Increasing water activity (0.28, 0.65, 0.90) increased losses of lysine and tryptophan but had no influence on the oxidation of methionine, the level of remaining hydroperoxides or 02 uptake. Hydrocarbons were decreased.

5. Limitation of 02 uptake to 1 mol/mol lipid instead of excess 02 (02 uptake about 2.5 mol/mol lipid in 4 weeks) significantly reduced the degradation of lysine and tryptophan but had less influence on the oxidation of methionine. The level of remaining hydroperoxides was increased but hydrocarbons were unaffected.

(Received May 08 1984)

(Accepted July 18 1984)

Correspondence:

p1 Building 1K40, Novo Industri A/S, Novo AIlé, DK-2880 Bagsvaerd, Denmark.

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