Although　nanosized　ingredients,　including　TiO2　nanoparticles　(NPs),　can　be　found　in　a　wide　range　of　consumer　products,　little　is　known　about　the　effects　these　particles　have　on　other　active　compounds　in　product　matrices.　These　NPs　can　interact　with　reactive　oxygen　species　(ROS),　potentially　disrupting　or　canceling　the　benefits　expected　from　antioxidants.　We　used　electron　spin　resonance　spectrometry　to　assess　changes　in　the　antioxidant　capacities　of　six　dietary　antioxidants　(ascorbic　acid,　α-tocopherol,　glutathione,　cysteine,　epicatechin,　and　epicatechin　gallate)　during　exposure　to　P25　TiO2　and/or　simulated　sunlight.　Specifically,　we　determined　the　ability　of　these　antioxidants　to　scavenge　1-diphenyl-2-picryl-hydrazyl　radical,　superoxide　radical,　and　hydroxyl　radical.　Exposure　to　simulated　sunlight　alone　did　not　lead　to　noticeable　changes　in　radical-scavenging　abilities;　however,　in　combination　with　P25　TiO2　NPs,　the　scavenging　abilities　of　most　antioxidants　were　weakened.　We　found　glutathione　to　be　the　most　resistant　to　treatment　with　sunlight　and　NPs　among　these　six　antioxidants.　©　2017　American　Chemical　Society.