Impact of fermentation and extrusion processing on physicochemical, sensory and bioactive properties of rice-black gram mixed flour

Current study details about the impact of solid state fermentation and subsequent extrusion on the physicochemical, sensory and bioactive properties of the rice-black gram dough. Influence of the solid-state fermentation was evaluated, at three levels of yeast concentration (1–3%), sugar (4–8%) and fermentation time (2–6 h). Fermentation resulted in decreased pH and residual sugar, from 6.38 to 5.41 and 1.07 to 0.69%, respectively, whereas the titratable acidity was increased from 0.86 to 1.79%, after 6 h of fermentation. Moreover, solid state fermentation for 6 h leads to increased total phenolic content, antioxidant activity and protein content from 29.80 to 44.12 mg GAE/100 g, 3.38–5.10 mg GAE/100 g and 10.36–13.65%, respectively. FTIR analysis showed decreased crystallinity up on fermentation. Subsequently, dough fermented for 6 h with 3% yeast and 4% sugar (optimized condition) was considered for the extrusion processing, which leads to increased phenolic content and antioxidant activity up to 77.3 mg GAE/100 g, and 11.39 mg GAE/100 g, respectively. Expansion ratio, bulk density, water solubility and water absorption index were determined for product characterization. Furthermore, extrudate prepared from the fermented flour had slightly higher acceptability (mean score: 4.12) than the unfermented counter part (mean score: 3.75) out of 5.