Study On Enzyme Activity And Physicochemicao Properties Of Wheat Bran During Solid State Fermentation

As an important by-product of wheat processing,wheat bran is a representative dietary fiber resource.Because most of the dietary fiber in bran is insoluble dietary fiber,but the content of soluble dietary fiber is very small,which seriously affects its application.Therefore,in this paper,the bran was fermented reasonably,the content of soluble dietary fiber in the bran was increased,and the enzymatic activity and physicochemical properties of the wheat bran in the fermentation process were identified.This has important theoretical and practical significance for improving the utilization value of wheat bran.In this paper,the extraction yield of soluble dietary fiber was used as an index to optimize the solid-state fermentation conditions of Rhizopus oryzae.On the basis of single factor experiment,response surface experiment was used to optimize the conditions of solid state fermentation,including substrate water content of wheat bran,inoculation amount of solid medium,particle size of wheat bran,and fermentation time of the solid state fermentation.The results are as follows: substrate water content of wheat bran,the inoculum amount of solid medium,the particle size of wheat bran,and the fermentation time of the whole solid-state fermentation were 55%,10%,50 mesh,and 120 h,respectively.Under these conditions,the yield of soluble dietary fiber was 9.33%.This fermentation method greatly increases the extraction yield of soluble dietary fiber.The changes of the two enzyme activities of amylase and protease during the solidstate fermentation of wheat bran were determined.Whether it is with the increase of the water content of the wheat bran matrix or with the extension of the solid-state fermentation time,the two enzyme activities were the same showed a trend of increasing first and then decreasing.Among them,amylase reached a maximum value of 0.013 U/g when the substrate moisture content was 55% and fermentation time was 96 h,and protease reached a peak value of 65.69 U/m L when the substrate moisture content was 45% and fermentation time was 120 h.In order to study the effect of solid state fermentation on the properties of wheat bran,the physical properties such as the central temperature,water activity and scanning electron microscope of wheat bran were monitored.The results showed that when the moisture content of wheat bran matrix was 55%,the highest central temperature was 28.90±0.36 ℃and the most suitable water activity range for microbial growth,and the degradation degree of wheat bran was the largest.At the same time,the chemical properties such as total phenolic content,flavonoid content,alkyl resorcinol content and antioxidant activity during the fermentation of wheat bran were monitored.The results showed that the total phenolic content and flavonoid content in the raw wheat bran were 1134.34 μg/g and 0.72 mg/g,respectively.The contents of total phenols and flavonoids in wheat bran increased significantly after fermentation,and reached the highest values when the substrate moisture content was 55% and fermentation time was 96 h and 72 h,respectively,with the contents of 3713.64 μg/g and 3.10 mg/g,respectively.The alkylresorcinol content hardly changed.The scavenging abilities of raw wheat bran to DPPH,ABTS and hydroxyl radicals were 12.23%,30.32% and 11.76%,respectively.When the water content of the substrate was 55%,the scavenging capacity of DPPH free radical reached the highest at 24.73% at 96 h of fermentation,and the scavenging capacity of ABTS and hydroxyl radical reached the maximum at 74.04% and30.91% at 120 h of fermentation,respectively.The absorbance value of the reducing power of the raw wheat bran was 0.461,and the absorbance value was 1.860 when the substrate water content was 55% for 120 h of fermentation,and the antioxidant activity was the strongest at this time.