Selenium, fibre, and protein enrichment of rice product: Extrusion variables and product properties

Abstract

Objectives: Rice has been identified as a high glycemic index (GI) food associated with obesity and diabetes. Current study investigated the replacement of rice flour and its effect on product properties using extrusion technology. Materials and Methods: High selenium yam and konjac flours were used to increase fibre and selenium contents, whereas sorghum and soy protein were added to improve protein content as well as textural properties of product. The following variables were optimized: yam flour (20% to 60%), feed moisture content (25% to 35%), and extrusion temperature (100°C to 120°C) by evaluating the breaking strength, firmness, colour, bulk density, and water absorption index (WAI) of the extruded products. Results: Results show that the extrusion temperature has a significant relationship with the products’ breaking strength, WAI, and bulk density, whereas the feed moisture content influenced the WAI, bulk density, and firmness (P < 0.05). The inclusion of yam flour significantly increased the firmness and yellowness (b* value) of the products (P < 0.05). Sensory profiling revealed that the enriched product has comparable textural properties (stickiness, firmness, and graininess) with the commercial rice. Comparing with commercial rice, the enriched product has significantly higher antioxidant activity (163.53 vs. 10.33 μmol Trolox/100 g, DPPH assay), protein (13.4% vs. 9.4%), fibre (12% resistant starch, 9% glucomannan), and a lower GI value (69.6 vs. 95.4). The enriched product also contains 15.62 µg/100 g selenium, providing additional health benefit as Se-enriched functional food. Conclusions: This work has demonstrated the suitability of applying extrusion to produce a healthier alternative rice product by nutrient enrichment via rice flour substitution.