Effect of Brewer's spent grain and temperature on physical properties of expanded extrudates from rice

- Expanded extrudates of rice and brewer spent grains (BSG) were produced.
- Addition of BSG reduced apparent density and volumetric expansion index.
- Barrel temperature caused an increase of the number of extrudate internal cells.
- BSG, up to 15%, could be used in combination with rice for puffed snacks.

Given the broad acceptance of extruded products in Brazil and the nutritional quality of rice and brewer's spent grain (BSG), this study aimed at evaluating the effect of extrusion temperature (100-160 °C) and amount of BSG (0-30% db) on physical properties of puffed snacks. Extrusion was carried out using a twin-screw extruder. A factorial design was proposed with two factors, temperature and BSG content, and three center points in order to analyze their influence on some response variables, such as specific mechanical energy (SME) input, output, frequency of structural ruptures, average specific force of ruptures, average puncture force and crispness work. SME input decreased significantly (P < 0.05) with an increase of BSG content. The output was not affected by temperature. The apparent density of expanded product increased with the addition of BSG. BSG was statistically significant and had a negative effect on volumetric expansion index. The frequency of structural ruptures was positively influenced by temperature that may have contributed to increase the number of bubbles (it could be translated in crispness). In conclusion, blends of rice flour and BSG have a good potential use as an additive for extruded snack production, reducing residue problems of brewer industries.