Determination of triacylglycerol oxidation mechanisms in canola oil using liquid chromatography\u2013tandem mass spectrometry

Shunji Kato,Susumu Takekoshi,Teruo Miyazawa,Takahiro Eitsuka,Yasuhiko Hanzawa,Yurika Otoki,Masayoshi Sakaino,Fumiko Kimura,Junya Ito,Takashi Sano,Naoki Shimizu,Kiyotaka Nakagawa

doi:10.1038/s41538-017-0009-x

Shunji Kato, Susumu Takekoshi + Show 10 more

Open Access

https://doi.org/10.1038/s41538-017-0009-x

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Abstract

Triacylglycerol (TG), the main component of edible oil, is oxidized by thermal- or photo- oxidation to form TG hydroperoxide (TGOOH) as the primary oxidation product. Since TGOOH and its subsequent oxidation products cause not only the deterioration of oil quality but also various toxicities, preventing the oxidation of edible oils is essential. Therefore understanding oxidation mechanisms that cause the formation of TGOOH is necessary. Since isomeric information of lipid hydroperoxide provides insights about oil oxidation mechanisms, we focused on dioleoyl-(hydroperoxy octadecadienoyl)-TG (OO-HpODE-TG) isomers, which are the primary oxidation products of the most abundant TG molecular species (dioleoyl-linoleoyl-TG) in canola oil. To secure highly selective and sensitive analysis, authentic OO-HpODE-TG isomer references (i.e., hydroperoxide positional/geometrical isomers) were synthesized and analyzed with HPLC-MS/MS. With the use of the method, photo- or thermal- oxidized edible oils were analyzed. While dioleoyl-(10-hydroperoxy-8E,12Z-octadecadienoyl)-TG (OO-(10-HpODE)-TG) and dioleoyl-(12-hydroperoxy-9Z,13E-octadecadienoyl)-TG (OO-(12-HpODE)-TG) were characteristically detected in photo-oxidized oils, dioleoyl-(9-hydroperoxy-10E,12E-octadecadienoyl)-TG and dioleoyl-(13-hydroperoxy-9E,11E-octadecadienoyl)-TG were found to increase depending on temperature in thermal-oxidized oils. These results prove that our methods not only evaluate oil oxidation in levels that are unquantifiable with peroxide value, but also allows for the determination of oil oxidation mechanisms. From the analysis of marketed canola oils, photo-oxidized products (i.e., OO-(10-HpODE)-TG and OO-(12-HpODE)-TG) were characteristically accumulated compared to the oil analyzed immediately after production. The method described in this paper is valuable in the understanding of oil and food oxidation mechanisms, and may be applied to the development of preventive methods against food deterioration.

Highlights

Edible oil is an essential food ingredient that is mainly composed of triacylglycerol (TG), and is widely used in various food products
During industrial or culinary processes, TG oxidizes to TG hydroperoxide (TGOOH) as the primary oxidation product by radical oxidation or singlet-oxygen oxidation (Fig. 1a),[1,2] and subsequently oxidized to various secondary oxidation products.[1,2,3]
We found that the use of alkali metals on ESI tandem mass spectrometry (MS/ MS) enables analysis of lipid hydroperoxide positional isomers,[31,32,33,34,35,36,37] and with the use of this technique, it was identified that the oxidation of phospholipids in mayonnaise was predominantly initiated by auto-oxidation.[37]

Summary

INTRODUCTION

Edible oil is an essential food ingredient that is mainly composed of triacylglycerol (TG), and is widely used in various food products. During industrial or culinary processes, TG oxidizes to TG hydroperoxide (TGOOH) as the primary oxidation product by radical (e.g., auto-, thermal-) oxidation or singlet-oxygen (e.g., photo-) oxidation (Fig. 1a),[1,2] and subsequently oxidized to various secondary oxidation products (e.g., aldehydes and carboxylates).[1,2,3] The sequential formation of these oxidative products deteriorate the oil quality such as nutritional value, flavor and taste, and exhibit various toxicities.[4,5,6,7,8] Staprans et al reported that dietary oxidized lipids are absorbed by the small intestine and distributed to lipoproteins and the liver.[9,10,11] The circulating (and/ or accumulated) oxidized lipids are presumed to play an important role in the development of various disorders such as cardiovascular disease,[12,13,14] Alzheimer’s disease,[15] and aging.[16,17] the prevention of TGOOH generation in oil is beneficial to our health and key to maintain the quality of edible oils Based on these facts, considerable attention has been paid on how to analyze TGOOH and to determine the cause of TGOOH generation.[18,19,20,21]. Because there are six types of HpODE isomers (i.e., 9-hydroperoxy10E,12Z-octadecadienoic acid: 9-EZ-HpODE, 9-hydroperoxy10E,12E-octadecadienoic acid: 9-EE-HpODE, 10-hydroperoxy8E,12Z-octadecadienoic acid: 10-HpODE, 12-hydroperoxy-9Z,13Eoctadecadienoic acid: 12-HpODE, 13-hydroperoxy-9Z,11E-octadecadienoic acid: 13-ZE-HpODE and 13-hydroperoxy-9E,11E-octadecadienoic acid: 13-EE-HpODE),[33] in this study, we analyzed each OO-HpODE-TG isomer including their sn-isomers (i.e., OO-HpODETG bearing HpODE isomers at sn-1 and sn-2 positions)

AND DISCUSSION

Findings

MATERIALS AND METHODS