Trapping of Carbonyl Compounds by Epicatechin: Reaction Kinetics and Identification of Epicatechin-adducts in Stored UHT Milk.

The kinetics of the reaction between epicatechin and various carbonyl compounds typically formed in cooked and stored foods were evaluated in model systems at pH 7.4 and 37 °C, and the corresponding reaction products in stored UHT milk added epicatechin were identified by HPLC-MS/MS. The rate constants for the reactions of carbonyl compounds with epicatechin decreased in the following the order: methylglyoxal; 1.6 ± 0.2 M-1 s-1 > glyoxal; (5.9 ± 0.3) × 10-2 M-1 s-1 ≥ 5-(hydroxymethyl)furfural; (4.0 ± 0.2) × 10-2 M-1 s-1 ≥ acetaldehyde; (2.6 ± 0.3) ×10-2 M-1 s-1 ≥ phenylacetaldehyde; (2.1 ± 0.2) ×10-2 M-1 s-1 ≥ furfural; (4.3 ± 0.1) × 10-3 M-1 s-1 > 2-methylbutanal and 3-methylbutanal; ~ 0 M-1 s-1. Reaction products generated by epicatechin and methylglyoxal, glyoxal, 5-(hydroxymethyl)furfural and acetaldehyde were detected in UHT milk samples by incubating milk samples with epicatechin at 37 °C for 24 h. The lack of reaction between epicatechin and phenylacetaldehyde, furfural, 2-methylbutanal and 3-methylbutanal in stored UHT milk may be due to their slow reaction rates or low concentration in stored UHT milk. It is demonstrated that epicatechin traps 5-(hydroxymethyl)furfural, acetaldehyde, glyoxal and methylglyoxal, and may thereby reduce off-flavour formation in UHT milk during storage both by trapping of precursors (methylglyoxal and glyoxal) for off-flavour formation and by direct trapping of off-flavours.