Extrusion of fermented rice-black gram flour for development of functional snacks: Characterization, optimization and...

Considering the health benefits of fermentation, extrusion of fermented rice black gram mix flour can lead to developing nutritionally rich expanded snack. Hence, present study details the effect of various extrusion process variables, barrel temperature (100, 110, 120 °C), screw speed (250, 300, 350 rpm) and die opening diameter (3, 3.5 mm) on physicochemical and bioactive properties of extrudates from fermented rice-black gram flour (Rice flour: black gram flour = 3:1). Results indicated that temperature rise led to the production of a more expanded product with higher water solubility index (WSI) and lower water absorption index (WAI). Higher puffing, WSI, and bioactive content were observed in 3 mm die opening extrudates. Interestingly, extrusion cooking of fermented flour has shown a remarkable increment in phenolic content and antioxidant activity from 63.47 up to 210.3 and 7.28 up to 13.889 mg GAE/100 g, respectively. However, rise in barrel temperature showed a negative impact on bioactive attributes. Further, the optimal conditions determined by numerical optimization method for development of fermented flour-based extrudates having superior functional and enhanced bioactive properties were found to be 100 °C temperature, 289 rpm of screw and 3 mm die diameter. Principal component analysis indicated that bulk density-moisture content and phenolic content-antioxidant activity were highly positively correlated, while expansion ratio-bulk density was negatively correlated. The microstructure of extrudates showed continuous and compact structure lacking starch granules. The fuzzy logic analysis revealed that fermented flour-based extruded product had superior overall acceptability over unfermented flour extrudates.