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The role of iron in peroxidation of PUFA: Effect of pH and chelators
Author(s) -
Mozuraityte Revilija,
Kristinova Vera,
Rustad Turid,
Storrø Ivar
Publication year - 2016
Publication title -
european journal of lipid science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.614
H-Index - 94
eISSN - 1438-9312
pISSN - 1438-7697
DOI - 10.1002/ejlt.201400590
Subject(s) - chemistry , chelation , autoxidation , liposome , citric acid , oxalic acid , solubility , inorganic chemistry , oxygen , polyunsaturated fatty acid , lipid oxidation , ethylenediaminetetraacetic acid , nuclear chemistry , antioxidant , biochemistry , fatty acid , organic chemistry
The aim of this work was to understand the effect of pH and chelators on free iron (Fe 2+ /Fe 3+ )‐mediated oxidation in liposome dispersions made of marine phospholipids. Consumption of dissolved oxygen was used to follow lipid oxidation. The highest oxygen uptake rates were found at pH 4–5. The increase in pH (>5.7) enhanced autoxidation rate of Fe 2+ to Fe 3+ and lowered solubility of Fe 3+ causing decrease in oxygen uptake rates. Simultaneously, the negative charge on the liposome vesicles increased with increasing pH improving the attraction between iron and liposomes. The retention of Fe 3+ ions by phospholipids is suggested to prevent complete precipitation of Fe 3+ at pH > 5, which facilitates a pro‐oxidative activity of iron even at higher pH. The tested chelators reduced Fe 2+ (10 μM) mediated oxidation at pH 5.5 and at 2:1 chelator‐to‐iron ratio in the following order: EDTA ∼ casein > citric acid > oxalic acid. However, when pH was reduced below the pKa of the EDTA carboxylic groups, EDTA lost its chelating abilities. The stability constants for complexes between the chelators and iron followed the same sequence as efficacy of the chelators at pH 5.5, making it an additional factor determining the efficacy of chelators. This study shows that the final oxidation rate is dependent on the overall dissolved iron in the system and the degree of attraction between iron and the surface of liposome vesicles at a given pH. Practical applications For successful addition of marine polyunsaturated lipids into emulsified food, it is important to understand how physicochemical conditions affect the pro‐oxidative activity of iron and the antioxidant activity of metal chelators. This work addresses the role of pH in oxidation of marine liposomes, and the knowledge may help to characterise effective hurdles for lipid oxidation. This study shows that pH has an impact on iron solubility and attraction between iron and the liposome surface and also affects the efficacy of EDTA. This study also shows that by quantification of the dissolved oxygen consumption, it is possible to screen and evaluate the impact of surrounding conditions (pH, chelators) on iron‐mediated oxidation in a water‐based system. The study shows that oxidation rate is dependent on the overall dissolved iron in the system and the degree of attraction between iron and the surface of liposome vesicles at a given pH.