Nat Prod Sci.  2017 Dec;23(4):247-252. 10.20307/nps.2017.23.4.247.

Rapid Identification of Methylglyoxal Trapping Constituents from Onion Peels by Pre-column Incubation Method

• Kim JH
• Kim MI
• Syed AS
• Jung K
• Kim CY

• KMID: 2401575
• DOI: http://doi.org/10.20307/nps.2017.23.4.247

Abstract

The methylglyoxal (MGO) trapping constituents from onion (Allium cepa L.) peels were investigated using pre-column incubation of MGO and crude extract followed by HPLC analysis. The peak areas of MGO trapping compounds decreased, and their chemical structures were identified by HPLC-ESI/MS. Among major constituents in outer scale of onion, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2) was more effective MGO scavenger than quercetin (6) and its 4"²-glucoside, spiraeoside (3). After 1 h incubation, compound 2 trapped over 90% MGO at a concentration of 0.5 mM under physiological conditions, but compounds 3 and 6 scavenged 45%, 16% MGO, respectively. HPLC-ESI/MS showed that compound 2 trapped two molecules of MGO to form a di-MGO adduct and compounds 3 and 6 captured one molecule of MGO to form mono-MGO adducts, and the positions 6 and 8 of the A ring of flavonoids were major active sites for trapping MGO.

Keyword

Allium cepa L.; Methylglyoxal trapping; Pre-column incubation; Flavonoids

MeSH Terms

Catalytic Domain
Chromatography, High Pressure Liquid
Flavonoids
Methods*
Onions*
Pyruvaldehyde*
Quercetin
Flavonoids
Pyruvaldehyde
Quercetin

Figure

• 

  Fig. 1. Scavenging of MGO by onion peel extracts (0.05, 0.25 and 0.5 mg/ml) under physiological conditions (pH 7.4, 37oC). Data are presented as the mean ± S.E. of three replications.

• 

  Fig. 2. Chemical structures of the identified components from onion peel extract. The compounds No. are the same as in Fig. 3. and Table 1.

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  Fig. 3. HPLC-DAD chromatograms of the onion peel extract. Onion peel extract dissolved in methanol (A), after incubation with PBS (100 mM, pH 7.4) for 12 h (B) and 10 mM MGO for 12 h, in PBS (C) at 37oC. The peaks designated as asterisk (∗) were potential MGO scavengers. Peaks 2-a, 3-a and 6-a appeared after reaction.

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  Fig. 4. MGO scavenging capacity of isolated compounds 2, 3 and 6 under physiological conditions (pH 7.4, 37oC). Purified compounds 2, 3 and 6 (0.25 or 0.5 mM) were incubated with MGO (0.33 mM) for up to 4 h. (A) 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2). (B) spiraeoside (3). (C) quercetin (6).

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  Fig. 5. MS spectra of MGO adducts and proposed structures mono- or di-MGO adducts of compounds 2 (A), 3 (B) and 6 (C) under physiological conditions (pH 7.4, 37oC).

Reference

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