The aim of this study was to determine the effects of extrusion processing variables on antioxidant activity (AA), total phenolic content (TP) and β-glucan content (BG) of extrudates. Products were prepared by extrusion cooking of barley flour, barley flour–tomato pomace and barley flour–grape pomace blends. Antioxidant activity as measured by the DPPH method was 43.17 ± 0.362, 27.57 ± 0.120 and 82.23 ± 0.785% while TPs, expressed as ferulic acid equivalents, were 5.29 ± 0.126, 4.66 ± 0.023 and 9.15 ± 0.015 mg g−1 dry sample in the extracts obtained from barley flour, tomato and grape pomaces, respectively. Extrusion cooking decreased AA and TP of barley, barley–tomato pomace and barley–grape pomace extrudates. Temperature and screw speed had significant (P < 0.05) effect on BGs of barley flour and barley–grape pomace extrudates. However, BG of tomato pomace blend extrudates had significantly (P < 0.05) influenced from pomace level only. Results indicated that the content of β-glucan is higher in barley flour than in extrudates of barley flour and pomace blends.