The Quality Improvement Of Whole Wheat Flour By The Stabilization Of Wheat Bran And Germ And Fine-ground Bran

Compared with refined flour,whole wheat flour with addition of wheat bran and germ,is rich in dietary fiber,vitamins,phenolic compounds,carotenoids,and so on,which is beneficial to prevention of type 2 diabetes,cardiovascular disease,obesity,cancer and other diseases.However,the instability of wheat bran and wheat germ and the rough texture of wheat bran lead to short storage period and poor palatability of whole wheat flour,which restricts the industrial development of whole wheat products.Therefore,it is significant to explore the most optimal storage conditions,stabilization methods,and the optimal bran size to extend the storage period of wheat bran and wheat germ and improve the quality of whole wheat dough.The storage quality of wheat bran and wheat germ under different storage methods were determined to explore the most suitable storage conditions.In addition,the effects of heat treatment and non-heat treatment on the enzyme inactivation of wheat bran and wheat germ were compared,and the most suitable stabilization method was explored.On this basis,the microwave-treated and the ultrasonic-treated wheat bran were ground and divided into three different particle sizes,which were added to the flour,respectively,to make whole-wheat dough and whole-wheat steamed bread.Then the effects of different stabilization methods and different particle sizes were explored.This study provided the basis for the optimal storage and the quality improvement of whole wheat products.The main findings in this study were summarized as follows:1.The effect of different storage conditions on the storage quality of wheat bran and wheat germ.The wheat bran and wheat germ of different packaging methods were stored at different temperatures for one month to determine the acid value,malondialdehyde value,color difference,lipase and lipoxygenase activity change.The results showed that the change trend of the five indicators of wheat bran was consistent with that of wheat germ.With the extension of storage time,the content of acid and malondialdehyde,and color difference of wheat bran and wheat germ increased,while the activities of lipase and lipoxygenase decreased.The higher the storage temperature was,the more obvious the change was.When the storage temperature is 4°C,the five indexes of wheat bran and wheat germ had little change over time.This showed that the increase of temperature was negatively correlated with the quality of wheat bran and wheat germ,as the quality of wheat bran and wheat germ can be better maintained at lower temperatures.At the same temperature,the acid value,malondialdehyde value,color difference,the lipase and lipoxygenase activities of woven bag packaging group changed more obviously than those of ziplock bag packaging.This showed that the ziplock bag packaging can slow down the deterioration of wheat bran and wheat germ.Under the same storage conditions,the changes of these five indicators of wheat germ were more significant than that of wheat bran,indicating that wheat bran is easier to deteriorate than wheat bran.2.The effect of different treatment methods on the stabilization of wheat bran and wheat germ.The optimal treatment conditions of wheat bran and wheat germ were explored.Five different heat treatment methods,hot air drying,infrared,microwave,atmospheric and high-pressure steam,for both wheat bran and wheat germ,and non-thermal stabilization ultrasound for wheat bran were tested,respectively.Then the heat-treated wheat bran and wheat germ were used for accelerated storage experiment.The results showed that microwave treatment,atmospheric steam,high-pressure steam treatment and ultrasonic treatment can all inactivate lipase and lipoxygenase,while the hot-air drying treatment and infrared treatment showed little effect.Besides,the acid value of wheat bran and wheat germ treated with microwave,atmosphere pressure steam,and high pressure steam was not changed obviously during the accelerated storage process.These results suggested that microwave,atmospheric steam,and high-pressure steam treatment can effectively improve the storage stability of wheat bran and wheat germ,and ultrasonic treatment can effectively inactivate lipase and lipoxygenase in wheat bran.3.The effect of microwave,ultrasonic treatment and different particle size wheat bran on the quality of whole wheat dough and steamed bread.After microwave and ultrasonic treatment,the wheat bran was ground and sieved into three particle sizes: coarse(280-450 μm),medium(154-180 μm),and fine(≤71 μm),which are added to the flour to make whole wheat dough and whole-wheat steamed.Then the effect of microwave and ultrasonic treatment and different particle diameters on the texture,dynamic rheological properties,free sulfhydryl groups and thermal properties of whole-wheat dough,as well as the specific volume,expansion ratio,color,sections,and sensory evaluation of whole wheat bread were measured.The results showed that with the decrease of the grain size of wheat bran,the hardness,tackiness and chewiness of the microwave treatment group declined,and the cohesiveness increased.The hardness,tackiness and chewiness of the ultrasonic treatment group were smaller than those of the microwave treatment group(P<0.05).The elastic and viscosity modulus of the microwave treatment group decreased with the decrease of the grain size of wheat bran.With the same grain size,the elastic and viscosity modulus of the ultrasonic treatment group were lower than that of the microwave treatment group.The free sulfhydryl content of each treatment group gradually decreased,and the free sulfhydryl content of the ultrasonic treatment group decreased greater than the microwave treatment group(P<0.05).The starch gelatinization temperature of each treatment group gradually increased,and the temperature of the ultrasonic treatment group was higher than that of the microwave treatment group.For the steamed bread,with the decrease of particle size,the specific volume,expansion ratio,profile height and sensory score of whole-wheat steamed bread gradually improved,and the ultrasonic treatment group was better than the raw wheat bran group.These results showed that both particle size reduction and ultrasonic treatment can improve the quality of dough and steamed bread.