Substantial differences and specific trends in antioxidant activity were not observed with respect to extrusion temperature. However, it is notable that improvement in antioxidant activity for extruded products containing apple pomace(28-31%) was more pronounced compared with those containing tomato pom ace(14-15%). Although it is known that thermal processing of tomatoes leads to improvement in the free-radical scavenging capacity of carotenoids, it is primarily attributed to an increase in the pool of bioaccessible lycopene(9). A different set of mechanisms might have been at work in the current study, including additive and synergistic effects of various phytochemicals, release of unidentified phytochemicals from the matrix, and/or pressure-induced isomerization of antioxidants such as lycopene to more bioactive conformations(9,24,27). The unique low moisture and high-pressure, shear, and temperature environment during thermomechanical extrusion processing may play a special role in this context.