4-Hydroxy-2-nonenal (4-HNE) and Its Lipation Product 2-Pentylpyrrole Lysine (2-PPL) in Peanuts

Abstract

After synthesis of a deuterated 4-hydroxy-2-nonenal (4-HNE) standard, the formation of 4-HNE during heating of peanut oil and whole peanuts, respectively, was measured by GC-MS. Whereas a significant increase in 4-HNE levels was observed for peanut oil, the amount of 4-HNE decreased when whole peanuts were roasted due to lipation reactions with amino acid side chains of the proteins. The ε-amino group of lysine was identified as the favored reaction partner of 4-HNE. After heating N(α)-acetyl-l-lysine and 4-HNE, a Schiff base, a novel pyridinium derivative, a 2-pentylpyrrol derivative and, following reduction and hydrolysis, a reduced, cyclized Michael adduct were identified. 2-Amino-6-(2-pentyl-1H-pyrrol-1-yl)hexanoic acid (2-PPL) was synthesized and quantitated in peanut proteins, which had been incubated with various amounts of 4-HNE by HPLC-ESI-MS/MS after enzymatic hydrolysis. At low 4-HNE concentrations the modification of lysine could be entirely explained by the formation of 2-PPL. Additionally, 2-PPL was quantified for the first time in peanut samples, and an increase depending on the roasting time was observed. 2-PPL represents a suitable marker to evaluate the extent of food protein lipation by 4-HNE.

Amounts of malondialdehyde do not accurately represent the real oxidative level of all vegetable oils: a kinetic study of malondialdehyde formation

“…The total difference of matrix, that is, vegetable oil and chicken meat seems to accounts for the discrepancy of results. It is well known that PUFA content is relatively low in animal fat and MDA can react with protein, amino acids and phospholipids, existing in chicken meat (Globisch et al ., ), which leads to the reduction in MDA content after a certain reaction time. In contrast, few protein and amino acids but the relatively high amount of PUFA was contained in vegetable oil.…”

The Chemistry of Protein Oxidation in Food

“…Additionally, lipids and lipid peroxidation products react with proteins without changing the oxidative status. Such reactions cannot be subsumed under “protein oxidation” but represent “lipation” reactions . This means, that the protein can be carbonylated but, at the same time, not oxidized (Figure ).…”

“…Moreover, other reactions of importance in food can lead to the formation of protein‐bound carbonyl compounds, for example glycation, lipation, and protein‐polyphenol reactions. Sugar degradation reactions provoke the formation of low molecular weight carbonyl compounds . Differently to enzyme‐catalyzed biochemical reactions with defined reaction products, protein oxidation is rather a random process leading to a multitude of reaction products; hence, the choice of a reliable marker for quantitative assessment is challenging.…”

Die Chemie der Proteinoxidation in Lebensmitteln

“…Auch Lipide und Lipidperoxidationsprodukte reagieren mit Proteinen ohne Änderung ihres oxidativen Status. Solche Reaktionen können nicht unter “Proteinoxidation” subsummiert werden, sondern stellen “Lipierungsreaktionen” dar . Dies bedeutet, dass Proteine zwar carbonyliert werden können, zugleich jedoch nicht oxidiert werden (Abbildung ).…”

“… Positionierung der “Proteincarbonylierung” zwischen definierten Proteinschädigungsreaktionen in Lebensmitteln . 4‐HNE: 4‐Hydroxynonenal, CML: N ‐ϵ‐Carboxymethyllysin, His: Histidin, Lys: Lysin, MDA: Malondialdehyd, MG‐H1: Methylglyoxal‐Derived Hydroimidazolone 1.…”