Glycation is regulated by isoflavones
The effect of soy isoflavones on the Maillard reaction (MR) was investigated. Model systems composed of the soy protein glycinin (10 mg mL−1) and fructose (40 mg mL−1) under basic pH (∼12) conditions were employed for testing the anti-glycative effect of the major antioxidant soy isoflavones (genistin and genistein at 10 μg mL−1) and a soy isoflavone-rich extract. The contents of total phenols (TPCs) and total flavonoids (TFCs) of the isoflavone-rich extract were determined. Glycinin was pre-incubated with isoflavones for 1 h and 16 h at 60 °C prior to MR. The progress of MR was estimated by analysis of free amino groups by OPA assay; carbohydrate covalently bound to the protein backbone using phenol-sulfuric acid assay, protein-bound Nε-(carboxymethyl)lysine (CML) by UPLC-MS and spectral analysis of fluorescent protein-bound AGEs. Genistin (10 μg mL−1, 23 μM) and its aglycone genistein (10 μg mL−1, 37 μM) did not prevent protein glycation (p > 0.05). The soy isoflavone-rich extract containing 2.5 mg mL−1 of TFC efficiently decreased the amount of carbohydrate bound to the protein skeleton (20%) (p < 0.05) and formation of advanced glycation end products (AGEs) (>80%) (p < 0.05). The anti-glycative mechanism of isoflavones may be related to its conjugation to glycation sites of the protein structure (free amino groups), their antioxidant character and trapping of dicarbonyl intermediates. Extracts based on mixtures of isoflavones may be useful for producing glycated conjugates avoiding the substantial formation of AGEs bound to protein.