Investigation of the effects of apple polyphenols on the chromatic values of weakly acidic lysine-fructose maillard system solutions

The effects of polyphenols on the chromatic characteristics of thermal processed apple slices during the Maillard reaction is unknown. Changes in the chromatic values (CIE L*, a*, b*) of the d -fructose/ l -lysine solution containing the apple polyphenol compounds chlorogenic acid, (+)-catechin, (−)-epicatechin and phlorizin on exposure to different temperatures, pH and incubation times were investigated. The results showed that (+)-catechin/(−)-epicatechin and phlorizin elevated the redness value (a*) and retarded 5-hydroxymethyl furfural (5-HMF) formation in d -fructose/ l -lysine solution at 90 °C and pH 4.0. Chlorogenic acid, on the other hand, boosted the yellowness (b*) value and accelerated 5-HMF formation. Browning was mainly observed in fructose/ l -lysine solutions after addition of catechin, the products of which were identified by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Five compounds (C21H23NO8, C21H28N2O8, C21H26O12, C27H37N3O10, and C27H40N2O14) were observed and their formation pathways were proposed. This demonstrates that catechin reacts with lysine, fructose or both at the para position of its B ring to form red-colored adducts, while simultaneously inhibiting 5-HMF formation. These results provide insights to explain and control browning in apple products.