³¹P NMR assessment of the phosvitin‐iron complex in mayonnaise

Abstract

Lipid oxidation is the main reason for the limited shelf life of mayonnaise. One of the main catalysts of this process is iron, which is introduced in its ferric (Fe(III)) form via phosvitin, an egg yolk phosphoprotein rich in phosphoserines. The binding of Fe(III) to phosvitin and its ability to establish a redox couple with Fe(II) is believed to determine the oxidation rate of unsaturated lipids. In this work, a 31P NMR based method was developed to quantify loading of phosvitin with Fe(III) and its reductive release. Both features could be quantified in model phosvitin solutions by exploiting the paramagnetic broadening of 31P NMR signal of phosphoserine residues by Fe(III). This method was then successfully applied to quantify the phosvitin‐Fe(III) loading in mayonnaise water phase by liquid NMR, whereas 31P NMR MAS could only provide a qualitative measure. The 31P NMR method showed a direct relation between loading of the Fe(III)‐phosvitin complex and lipid oxidation.

Evaluation of PBN spin-trapped radicals as early markers of lipid oxidation in mayonnaise

“…Here, EDTA worked as expected as a secondary antioxidant through the chelation of iron to inhibit the catalysing effect of this transition metal. The redox Fe 2+ /Fe 3+ cycling catalytic action is reported to go primarily via existing LOOHs (Laguerre et al, 2020;Merkx, Delić, Wierenga, Hennebelle, & van Duynhoven, 2019;Mozuraityte, Rustad, & Storro, 2008). These LOOHs could decompose to form LOO% and LO% radicals, which will respectively fuel the propagation of LOOH generation and form aldehydes via beta-scission of LO% (Fig.…”

Quantitative Spatiotemporal Mapping of Lipid and Protein Oxidation in Mayonnaise

“…In the non-stripped sample II (SO + aa), the antioxidant role of ascorbic acid for lipids is dominant over a pro-oxidant effect via redox cycling of transition metals, likely ferric (Fe 3+ ) to ferrous (Fe 2+ ) ions, at the lipid droplet interface (Figure 4A). We note that all mayonnaises in this study were prepared at low pH, where reduced binding strength to phosvitin allows for effective ferric-ferrous redox cycling [22,34]. In the stripped sample IV (SSO + aa), the ascorbic acid can no longer work in synergy with tocopherol and its pro-oxidant role becomes dominant (Figure 4B).…”

Multi-scale imaging of protein oxidation in mayonnaise

“…Reactions between alkyl radicals (L•) and molecular oxygen generate peroxyl radicals (LOO•), which 28 further accelerate lipid peroxidation by reacting with unsat-29 urated lipids. Whereas at neutral pH pro-oxidant iron ions 30 are strongly bound to the negatively charged phosvitin, a 31 weaker binding at the acidic pH of mayonnaise makes them 32 available as catalysts for lipid oxidation (Merkx et al, 2019). 33 Therefore, ethylenediaminetetraacetic acid (EDTA) is often 34 added to mayonnaise to bind free metal ions via chelation 35 and thus reduces the formation of lipid peroxidation (LPO) 36 products (Lee and Decker, 2011;Nielsen et al, 2004).…”

“…To validate that the accumulation of CAMPO-AFDye 647 at droplet interfaces is due to protein free radical formation induced by nearby lipid radicals, the pH of the mayonnaise was varied. Under the usual acidic environment of mayonnaise, phosvitin has weak affinity for ferric ions which allows them to act as a catalysts for lipid oxidation at oil/water droplet interfaces (Merkx et al, 2019). At neutral pH, phosvitin has a stronger binding affinity for ferric ions than acidic pH thus preventing ferric ions to be released at the interface (Castellani et al, 2004).…”