Composition, bioactive constituents and glycemic index of brown rice-watermelon seeds extruded snacks as stimulated by extrusion conditions

Abstract

Broken brown rice is usually categorised as raw material with low market value while watermelon seeds are discarded as waste. Therefore, this study aimed to develop brown rice-watermelon seeds extruded snacks by evaluating the effects of extrusion conditions (feed moisture content (12–16%), exit barrel temperature (120 -140ºC), and barrel screw speed (300 rpm - 420 rpm)) on its composition, bioactive constituents, and glycemic index. Polynomial regression was used to model the composition, bioactive constituents, and glycemic index while response optimizer was used to optimise the protein content of the extruded snacks. At a mixing ratio of 90% brown rice flour and 10% watermelon seeds powder, the effect of extrusion conditions on the moisture content of the extruded snacks ranged from 3.03 to 4.57%, protein content (11.24 to 16.20%), crude fat (0.77 to 1.08%), crude fibre (2.07 to 2.77%), ash (2.05 to 2.63%) and carbohydrate (73.66 to 79.36%). The total phenolic content of the extruded snacks ranged between 8.14 and 10.15 mg GAE/g, total flavonoid content (1.8 and 2.11 mg QE/100 g), DPPH radical scavenging activity (10.05% and 14.22%), and Glycemic index (60.00 and 67.24). The regression models showed the adequacy to predict the composition, bioactive constitutes and glycemic index of the snacks while the optimum conditions gave extruded snacks with 17.71% protein content. The glycemic index of the extruded snacks is intermediate. Conclusively, the developed extruded snacks served as an avenue to exploit the usage of underutilized broken brown rice and watermelon seeds to produce nutrient-rich value-added extruded product.