Twin-Screw Extrusion of Pre-Germinated Brown Rice: Physicochemical Properties and γ-Aminobutyric Acid Content (GABA) of Extruded Snacks

Pre-germinated brown rice (PGBR) from non-glutinous (KDML 105) and glutinous (RD 10) varieties was produced by a soaking method in cool water at 25 degrees C for 48 h. After germination, increased crude fiber, reducing sugar (P <= 0.05) and the gamma-aminobutyric acid (GABA) content (P <= 0.01) and decreased fat were observed. The extrusion was carried out in a twin-screw extruder by a central composite design (CCD) which studied the effect of feed moisture (15.6-22.3%), screw speed (264-434 rpm) and pre-germinated glutinous brown rice flour level (0-63.6%) on the physicochemical properties of extruded snacks (expansion ratio, density, hardness, brittleness, water absorption index (WAI), water solubility index (WSI)) and GABA content. Second-order polynomial models were computed and used to generate surface plots. Increasing the feed moisture increased the density (P <= 0.01) hardness and WAI, and decreased the expansion ratio, brittleness (P <= 0.01) and WSI (P <= 0.05). Increasing the screw speed increased the expansion ratio, brittleness, WAI and WSI, and decreased the density and hardness. Increasing the levels of pre-germinated glutinous brown rice flour increased the expansion ratio (P <= 0.01), brittleness, WSI (P <= 0.01) and the GABA content (P <= 0.01), and decreased the density, hardness (P <= 0.01) and WAI (P <= 0.01), while the feed moisture content and screw speed had no significant effect on the GABA content (P > 0.05). This knowledge can be used in the design of customer-oriented extruded PGBR products.