Effects Of Flexible Debranning On The Qualities Of Wheat Kernels And Flour

With the increasing pursuit of healthy and balanced diet by the public,wheat processing methods are also developing constantly.Wheat is rich in many kinds of nutrients,but the distribution is not balanced.The separation of bran and germ from endosperm as by-products in traditional flour milling process lead to the loss of nutrients,such as dietary fiber,protein,B vitamins and minerals.Whole wheat flour and its products have a rough taste due to the high content of bran,and the pollution factors contained in the outer pericarp of the grains may bring safety risks to whole wheat flour.In order to improve the problems of the nutrients loss during the traditional milling process,the coarse taste of whole wheat flour,and the high safety risks,the flexible debranning technology as the main treatment method was used in this study to investigate the changes of wheat kernels'structure and the main nutrients in each part of the bran under different debranning rates.And the water distribution in the debranned kernels during the process of wheat tempering were determined by the low field nuclear magnetic resonance(LF-NMR).Then,the effects of flexible debranning technology on the nutrition,safety and processing quality of wheat flour obtained by total grinding and Buhler Mill of the above kernels were investigated,respectively.The aim was to find an appropriate debranning rate which could not only retain the nutrients in wheat kernels but also reduce the safety risk,so as to provide basic theoretical support for the development of high-nutrition wheat flour and functional foods.Firstly,wheat kenels with debranning rates of 0,5,10,15 and 20%were obtained by using flexible debranning machine for 0?240 s.Scanning electron microscopy(SEM),fluorescence microscopy and light microscopy were used to observe the microstructures of the debranned kernels and the pearlings,and the contents of nutrients in each bran layer and the changes of microbial contents in the debranned kernels were determined.The microstructures of kernels and pearlings showed that when the debranning rate was 5%?20%,the pericarp,intermediate layer(including endocarp,seed coat and nucellar),aleurone layer and part of endosperm could be stripped off respectively.The results of nutrients'contents showed that the pearlings with debranning rate of 0?5%were rich in arabinoxylan,and the pearlings of 5?10%had the highest content of alkylresorcinol.Total phosphorus and total phenol were enriched in the pearlings of 10?15%,while the pearlings of 15?20%contained part of endosperm,so the contents of starch were higher.The results of the safety indexes in the debranned kernels showed as follows:5%debranning rate could reduce the total number of bacterial colonies,molds and yeasts by about 70%,and decrease the contents of lead(Pb)and cadmium(Cd)by 34%and 50%.The arsenic(As)was not detected in all samples.The distribution of water in the debranning kernels during the traditional tempering process showed that when the debranning rate was 5%,T₂₁ and A₂₁ reached equilibrium at about 10 h,and the water in the grains was evenly distributed.When the debranning rate was 10%,T₂₁and A₂₁ did not change at 8 h.When the debranning rate reached more than 15%,T₂₁ and A₂₁tended to be stable after 6 h.However,the water distribution of undebranned kernels was not even at 13 h.Then,a part of the debranned grains were completely milled by hammer cyclone mill.The effects of debranning on the dietary fiber,falling number,gluten properties,minerals,B vitamins,microbial content and thermomechanical properties of the wheat flour were investigated.The results showed that with the increase of debranning rate,the dietary fiber content in wheat flour decreased gradually,while the falling number,gluten index and brightness increased continuously.Wheat flour with a debranning rate of 5%could retained about 90%of the B vitamins and minerals in whole wheat four.When the debranning rate was 10%,the total number of colonies,molds and yeasts could be reduced by about 75%,and the contents of Pb and Cd were significantly decreased(P<0.05).The thermomechanical characteristics of wheat flour were determined by Mixolab,and the results showed that with the increase of debranning rate,C3(display of starch retrogradation properties),C4(display gelatinization stability of starch),C5(display cooling stage of gelatinized starch retrogradation characteristics)all increased,indicating that debranning could improve the pasting stability of starch and reduce the hindrance of bran on the rearrangement of starch molecules,making the starch easy to retrogradation.Meanwhile,another part of debranned kernels were milled by Buhler Mill.The flour yield and the contents of B vitamins,minerals and amino acids in wheat flour under different debranning rates were compared,and the pasting properties of wheat flour were analyzed.With the increase of debranning rate,the flour yield increased by about 3%.Compared with the undebranned wheat flour,the contents of VB₁,VB₂ and VB₆ in the wheat flour with the debranning rate of 10%increased by 15?17%,22?24%and 12?16%,respectively.The contents of magnesium(Mg)and potassium(K)in wheat flour reached the maximum at the debranning rate of 5?10%,and the iron(Fe)reached the maximum at the 10%debranning rate.There were no significant differences in the contents of calcium(Ca),sodium(Na)and copper(Cu)(P>0.05).Most essential amino acids in the aleurone layer were retain into the wheat flour at 5%debranning rate.The peak viscosity,trough viscosity,final viscosity and setback viscosity of wheat flour all decreased first and then increased,and the breakdown viscosity was significantly decreased at the debranning rate of 20%(P<0.05),while the pasting temperature had no significant change(P>0.05).