Influence of aggregation on the antioxidative capacity of milk peptides

This study investigated the effects of pH and addition of genistein prior to freeze-drying on the aggregation of reconstituted antioxidative milk peptides. The peptides having molecular masses below 6.5 kDa aggregated into higher mass aggregates of 16.9 kDa after tryptic hydrolysis for 30 min. Subsequent freeze-drying at pH 2.0 further promoted the aggregation of peptides to aggregates of 26.6 kDa, both in the absence and presence of genistein. The reconstituted peptides clustered into macroaggregates of 6 μm, having oxygen radical absorbance capacity (ORACFL) between 0.07 and 0.22 μmol Trolox equivalent (TE) mg−1 protein. Although freeze-drying at pH 6.5 promoted the aggregation of peptides, the reconstituted peptides retained a size of 150–170 nm and had an ORACFL of 0.59–0.88 μmol TE mg−1 protein. The addition of genistein synergistically increased Trolox equivalent antioxidant capacity, compared with the reconstituted milk peptide alone (P < 0.05).