Effects Of Milling Conditions On Quality Of Rice Flour

Rice is the most important crop in China and is also the foundation of our national economy.Milling is an important part of rice processing.More and more rice is processed into rice flour for production and living.Milling conditions can really effect the quality of rice flour.However,the study on effects of milling conditions combined speed and duration on the quality of rice flour is limited.In this study,waxy,low-and high-amylose rice were hulled,milled at different speeds(1050 r/min,950 r/min,750 r/min)for 20 s,40 s,60 s and grounded to obtain 30 rice flour samples.The physicochemical properties were investigated.The eating quality and rheological characteristics of the samples were also determined.And established mathematical model.This study showed that both milling duration and speed impacted the physicochemical and digestibility properties of different rice flours,but to different extents.With the increasing of milling time and speed,the degree of milling increased to 8.2%,7.3%,10.5%,and amylose content were increased to 1.15 and 1.09 times for low-and high-amylose content cultivar.This is related to the molecular structure of starch,mechanical force and rice cultivar.The swelling power was increased with milling duration and speed compared to unmilled rice flour.The solubility of milled rice flours was related to the cultivar,the solubility of waxy varieties is higher than 5.34%,while the high amylose content ones is higher than 2.48%..The peak viscosity of low-and high-amylose rice flour was more affected by milling duration,whereas the final viscosity was more affected by milling speed.Milling duration was a greater determinant of thermal properties than was milling speed.In terms of eating quality,theappearance,color,viscosity,taste and texture of rice flour improved with the milling time and speed increasing.However,the smell of rice flour was increased at first and then decreased with the milling time and speed increasing,which was related to the change of chemical composition of rice flour.Milling speed had less effect on digestibility than did milling duration for waxy rice flour,but speed had a greater effect on the digestibility of low-and high-amylose rice flour.Correlation analysis found that amylose content is the most important factor affecting rice flour's quality.And it is found that the model has the best fitting effect on thermal properties and is more suitable for low-and high-amylose content cultivate than the waxy rice flour.The rheological test showed that the suspension of rice flour was presenting shear-thinning property.During rice milling,the shear stress of rice flour increases and the viscosity decreases.Shear stress was consistent with Herschel-Bulkley model.Viscosity of waxy rice flour and low-amylose content rice flour were consistent with Williamson's model,while viscosity of high-amylose content rice flour met Cross model.Dynamic rheological properties shows milling increased the storage modulus of waxy rice flour,but decreased the storage modulus of low-amylose and high-amylose content rice flour.This study provided some information and technical for improvement of rice flour industrial production.