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Proanthocyanidins (PA) strongly complex with proteins and may be exploited to naturally expand gluten functionality. This study investigated the effect of PA with different MW profiles (from sorghum & grape seed) compared to monomeric catechin, on wheat gluten properties. Two gluten profiles were used: a bread wheat with a high ratio of high molecular weight glutenin subunits (HMW-GS) (SG) & a deletion line with reduced HMW-GS content (WG). PA were added at 0.8-2.5 mg/g flour or purified gluten. PA, dough, & gluten profiles were analyzed by HPLC & rheological methods. Sorghum PA was more (91%) polymeric than grape PA (42%). Mixograms & extensibility data showed catechin significantly (p<0.05) weakened dough, as expected of an antioxidant. However, grape & sorghum PA strengthened dough by increasing mixing tolerance, peak time, & force to extend dough. Sorghum PA had a greater strengthening effect. Retarded compliance (J1) in WG decreased from 3.5 (control) to 3.0 & 1.9 KPa-1 with grape & sorghum PA, respectively (at 2.5 mg/g flour). This indicates sorghum PA produced a stiffer structure. Catechin increased deformation to 4.1 KPa-1. Similar but less differentiated trends were seen in SG. Sorghum PA also reduced deformation vs control for WG (4.5 vs 14.4 KPa-1, respectively) & SG (1.0 vs 2.8 KPa-1, respectively) in purified glutens. Size-exclusion chromatography on SG showed sorghum PA increased insoluble polymeric protein (IPP) significantly vs other treatments & control (12.3 vs 8.2-8.4 AU, respectively). In WG, both sorghum & grape PA increased IPP (9.1 & 7.5 AU, respectively) compared to catechin (4.1) & control (4.3). The evidence suggests higher MW sorghum PA, crosslinked gluten more effectively than grape seed PA. Additional work is investigating the nature of the interactions. Sorghum PA is a promising natural ingredient to improve & expand gluten functionality.