Abstract: 【Objective】Effects of brown rice flour on the thermomechanical and dynamic rheological properties of wheat flour dough as well as physical and sensory characteristics of the cookies were investigated. The aim of the research is to provide a basis for further utilization of brown rice in developing new food products.【Method】 Mixolab and dynamic rheometer were employed to study the effects of brown rice flour replacement on rheological properties of wheat flour dough. The dough microstructure was observed by scanning electron microscope (SEM). Cookies were prepared and tested to investigate the effects of brown rice flour replacement on cookie quality characteristics. 【Result】 With the addition of brown rice flour, the water absorption of the flour dough and the degree of protein weakening increased, while dough development time and stability time decreased. The addition of brown rice flour diluted the concentration of gluten and destroyed the continuous state of the flour dough, which resulted in being difficult to form the stable gluten network structure, and subsequently leading to higher degree of protein weakening under double effects of mechanical force and heating. The increase of replacement ratio of brown rice flour decreased the temperature of starch gelatinization, peak and break down viscosity of the mixed flour, and setback value of the starch due to the higher degree of starch hydrolysis. It was shown from dynamic rheological studies that with the addition of brown rice flour, the dough remained viscoelastic system and storage modulus and loss modulus increased, while tan δ of the dough decreased, indicating higher degree of molecular cross-linking and elastic proportion in the mixed system. From SEM, with the addition of 10% brown rice flour, the dough microstructure became loose with small cracks and starch granules distributed unevenly. Irregular shape of rice starch granules could be observed and their adhesion force to dough surface significantly decreased. With further increase of replacement ratio, more and more big cracks could be observed and fibres were exposed to the dough surface. With the addition of brown rice flour, the width and expansion ratio of the cookies increased, whereas the thickness, hardness, score of taste, color, flavor and overall acceptability all decreased, especially score of color and flavor, indicating that existence of rice bran made the processed food hard to be acceptable due to high content of fibres, and especially its unpleasant smell and dark color. 【Conclusion】 The addition of brown rice flour made the wheat flour dough more elastic, but not beneficial to the stability of the dough. The rice bran, especially its unpleasant odor and dark color, is still the key factor affecting the acceptability of processed foods.

Key words: brown rice flour , wheat flour dough , rheological properties , cookie , quality characteristics