The present research aimed to assess how heating at 95 degrees C for 1 h followed by proteolysis affects the antioxidant properties of Maillard reaction mixtures constituted by soy protein isolate (SPI) and fructooligosaccharides (FOS) in 0.5 M phosphate buffer pH 7.4. Solutions of protein and sugars were also heated alone as controls. Glycation and cross-linking of protein was estimated by o-phaldialdehyde assay. Samples were hydrolyzed in vitro mimicking gastro-intestinal conditions and subsequently submitted to analysis. In vitro antioxidant properties were determined by LDL oxidation and oxygen radical absorbance capacity assays. Simultaneously, undigested reaction mixtures constituted by SPI and sugars were heated, fractioned by ultrafiltration and the fractions were characterized. Although Maillard reaction might give rise antioxidants, present data seem to indicate that neoantioxidants able to prevent LDL oxidation and to scavenge peroxyl-alkyl radicals were majority formed by thermal degradation of FOS (caramelization). Peptides derived from soy protein scavenged peroxyl radicals and did not protect LDL against cupper oxidation. (C) 2008 Elsevier Ltd. All rights reserved.