Are the major antioxidants derived from soy protein and fructo-oligosaccharides model systems colored aqueous soluble or insoluble compounds?

The present research aimed to determine the overall antioxidant capacity of solid model glycation systems based on either defatted soy flour or soy protein isolate as protein sources and fructo-oligosaccharides (FOS). In addition, we try to gain insight into the physicochemical characteristic of the major neo-antioxidants generated during heating of the model systems. These compounds may be formed in thermally processed foods containing as ingredients both components soy proteins and FOS. Samples constituted by protein source and FOS alone were employed as controls. The Maillard reaction was induced by heating at 150 °C for 1 h. Formation of colored compounds was detected by measuring the absorbance at 420 nm wavelength. The overall antioxidant capacity of the samples was either directly measured by the QUENCHER (quick, easy, new, cheap and reproducible) approach concept adapted to the ORAC_FL assay or indirectly by summing the ORAC values obtained by analysis under ORAC_FL standard conditions of aqueous and ethanol fractions of the samples. The sets of data were compared. The relationship between browning and antioxidant capacity was investigated. All samples excepting unheated FOS showed antioxidant capacity. Data seem to indicate that the QUENCHER approach allowed to determine in a single step, the overall antioxidant capacity of FOS caramels and thermally processed glycation mixtures leading to significant compositional changes as results of the simultaneous occurrence of reactions, such as Maillard, caramelization and thermoxidation. Our results also suggested a major formation of aqueous-soluble colored antioxidants from caramelization and Maillard reactions.