Abstract: To investigate the combined effect of enzymatic pretreatment and extrusion on the quality characteristics of brown rice flour, extruded brown rice flours with and without enzymatic pretreatment (control) from ordinary, red and black brown rice were examined for water solubility index, water absorption index, agglomeration rate, dispersion time, paste viscosity, color, gelatinization degree, sensory evaluation score, starch, reducing sugar and protein contents, and in vitro starch and protein digestibility. The results showed that compared with direct extrusion, enzymatic pretreatment combined with extrusion increased the water solubility index of ordinary, red and black brown rice flours by 3.04, 2.35 and 2.71 times, decreased the water absorption index by 67.87%, 60.96% and 62.17%, elevated the agglomeration rate by 6.44, 7.27 and 4.07 times, and reduced the dispersion time by 66.61%, 61.79% and 64.30%, respectively. Moreover the combined treatment decreased the viscosity of brown rice paste and weakened the shear-thinning behavior and the viscosity curves were more flat with it. The combined treatment reduced the starch content of ordinary, red and black brown rice flours by 29.22%, 28.71% and 26.70%, and the gelatinization degree by 19.53%, 8.94% and 13.13%; and increased the soluble protein content by 2.50, 3.87 and 3.27 times, respectively. All of these changes were statistically significant (P < 0.05). The color difference (ΔE) values of extruded ordinary, red and black brown rice flours with enzymatic pretreatment were 3.01, 4.66 and 3.28, respectively The combined treatment augmented slightly lightness value, reduced the percentage of rapidly digestible starch, increased the percentage of slowly digestible and resistant starch, enhanced the in vitro digestion rate and digestibility of protein, and resulted in significantly higher sensory evaluation scores (P < 0.05). The above data demonstrated that combined enzymatic pretreatment and extrusion improved the dispersibility of brown rice flour, reduced the paste viscosity, and increased sensory evaluation scores and protein digestibility in vitro. In conclusion, enzymatic pretreatment combined with extrusion can be viewed as a new approach for the processing and utilization of brown rice and has potential for application in cereal processing.

Key words: whole grain, brown rice flour, combined enzymatic pretreatment and extrusion, dispersibility, quality properties