Stability of isoflavones during extrusion processing of corn/soy mixture

The influence of extrusion processing in the presence of corn on the quanti ty and quality of genistein, daidzein, and their respective beta-glucoside, acetyl glucoside, and malonyl glucoside derivatives was evaluated. Product s of 100% soy (textured) and a blend of 20% soy protein concentrate (SPC) a nd 80% corn meal (direct-expanded) were extruded, with evaluations before a nd after extrusion. In addition, a 3 x (3 x 3) split-plot factorial experim ent investigated the influence of barrel temperature (110, 130, 150 degrees C), moisture content (22, 24, 26%), and relative residence time (1, 0.8, 0 .6) on extruder response and isoflavone profile. The extrusion barrel tempe rature had the most influence on isoflavone profile, especially decarboxyla tion of the malonyl beta-glucoside, followed by the moisture content. The a mount of extractable isoflavones decreased after extrusion for both the SPC and SPC/corn meal blend when extracted with 80% aqueous methanol but remai ned approximately the same when first hydrated with water before extraction . However, initially hydrating with water produced enzymatic glycolysis in the unextruded samples, increasing the aglycons dramatically.