Glycerol-bound oxidized fatty acids: formation and occurrence in peanuts

Abstract

For peanuts, roasted at 170 °C, the formation of selected glycerol-bound oxidized fatty acids (GOFAs), namely 9-oxononanoic acid (9-ONA), azelaic acid (AZA) and octanoic acid, was observed by GC-MS (EI). The content of octanoic acid as well as AZA increased with continuous roasting time (from 59 mg/kg peanut oil to 101 mg/kg peanut oil and from not detectable to 8 mg/kg peanut oil, respectively), whereas the content of 9-ONA initially decreased from 25 mg/kg peanut oil to 8 mg/kg peanut oil (20 min) and increased again up to 37 mg/kg peanut oil following roasting for 40 min. Due to its aldehyde function, 9-ONA could contribute to amino acid side chain modifications as a result of lipation, which could directly influence the functional properties of peanut proteins. Both 9-ONA and octanoic acid are potential markers of thermal processes. Furthermore, in model experiments using methyl linoleate and methyl oleate, up to 18 oxidized fatty acids could be identified as methyl esters, 9-ONA as well as octanoic acid as major components and a faster formation of GOFAs under roasting conditions (170 °C, 20 min). In addition, 9-ONA contributes to the formation of AZA and octanoic acid in both free and bound form as a result of oxidative subsequent reactions in presence of iron (III).

9-Oxononanoic Acid and Its Lysine Schiff Base Adduct as a Novel Lipation Product in Peanuts

“…Furthermore, the sample was filtrated (Whatman 595.5) and the solvent was completely rotated off under vacuum at 40 °C and 600 mbar. 1 Sample Preparation for Quantitation of 9-ONA in Peanuts. Approximately 100 mg of cold extracted peanut oil was weighed into a 14 mL Greiner tube.…”

“…The peroxide value (POV) was determined as described elsewhere. 1 5.0 g of native peanut oil was used.…”

“…The results for native peanut oil ensure that the methyl ester of 9-ONA was not artificially reproduced in significant amounts during transmethylation and measurement by GC−MS (EI), which is also confirmed due to the results of our previous studies. 1 In raw peanuts, a content of free 9-ONA of 1010.3 μmol/kg protein or 247.5 μmol/kg peanut (174.0 mg/kg protein or 42.6 mg/kg peanut, respectively) was determined. The fact that substantial amounts of 9-ONA were present in the raw peanuts points to an induction of the LPO during drying and storage of the raw peanuts (Figure 2).…”

“…Due to its aldehydic function, 9-ONA is able to modify nucleophilic side chains of protein-bound amino acids and, therefore, possibly contributes to the observed modification of lysine during roasting peanuts. 1,7 Amino Acid Modifications in Methyl 9-ONA-Modified Peanut Proteins. To determine the reactivity of 9-ONA toward nucleophilic side chains of protein-bound amino acids, methyl 9-ONA was incubated with peanut proteins extracted from native peanuts for 24 h at 37 °C in phosphate buffer (0.1 M, pH 7.4) under a nitrogen atmosphere.…”

“…Its formation is possible, for example, from hydroperoxides of mono- (e.g., oleic acid) and polyunsaturated fatty acids (e.g., linoleic acid). Besides octanoic acid (non-reactive GOFAs), 9-ONA (reactive GOFAs) is a major component of GOFAs and a potential marker of thermal processes such as roasting. − Recently, Störmer et al were able to determine for the first time selected GOFAs, namely, 9-ONA, azelaic acid, and octanoic acid, as their corresponding methyl esters in peanuts roasted at 170 °C. 9-ONA was quantitated in roasted peanuts with contents ranging between 8 and 37 mg/kg in peanut oil by means of GC–MS (EI) .…”