Preparation Of Xylooligosaccharides-enriched Wheat Bran Beverage Via Enzymatic Approach

This paper reported an enzymatic approach of preparation of xylooligosaccharides(XOS) -enriched wheat bran beverage, which is easy to realize in industry. The unpleasant flavors of wheat bran were removed and new flavors were formed through the baking process. Xylanase was used to hydrolyze arabinoxylan in wheat bran to functional XOS. Flavorzyme was used to hydrolyze proteins to peptides. Mid-temperatureα-amylase was used to hydrolyze starch to small molecule carbohydrates. Soluble mineral, vitamins were also remained in the wheat bran beverage. The processing can achieve the goal of full use of the active ingredients in wheat bran. The as-prepared XOS-enriched wheat bran beverage has a unique flavor and high nutritional value.The results concluded from experiments were as follows.Effects of the baking process on xylan conversion yield and sensory evaluation have been studied and the optimal baking conditions were: 180℃and 20 min. On the basis of the results of SPME-GC-MS, aldehydes were reduced while pyrazines, furfural and 5-methyl-2-furfural were increased by baking, in comparison with that unbaked wheat bran. The new compounds have made remarkable contribution to the fine flavor of baked wheat bran.Xylanase, flavorzyme and mid-temperatureα-amylase were used to hydrolyze the xylan, protein and starch in baked wheat bran, respectively. Optimal conditions of the orthogonal experiments based on the single-factor experiments were solid to liquid ratio 1:8, pH6.0, 153 U/(g wheat bran) xylanase, 138 U/(g wheat bran) flavorzyme, 60 U/(g wheat bran) mid-temperatureα-amylase, reaction temperature 50℃and reaction time 4 h. Xylan conversion yield was 52.02%, reducing sugar concentration was 27.19 mg/mL, protein extraction rate was 40.14%. XOS(xylobiose to xylotetrose) content was 6.19 mg/mL in the enzymatic hydrolysates. Most of proteins were hydrolyzed into peptides.Enzymatic hydrolysates were diluted to 3 times. Clarification optimal conditions were 0.1 g/L chitosan and 0.2 g/L bentonite, reaction time 30 min, centrifuged at 4000 r/min for 5 min. Seasoning optimal conditions were 10 g/L honey, 60 g/L sugar, 0.75 g/L citric acid. On the basis of SPME-GC-MS, new flavors, including pyrazines, pyrroles and pyridines were synthesized in baked wheat bran beverage. The formation mechanism of flavors were also discussed.Wheat bran beverages were stored at 4℃, 25℃and 37℃, respectively. During the storage, bacteria and E.coli in wheat bran beverages were both not detected. During 37℃storage, the soluble solids content quickly decreased. Color became deep dark and the rate of deposition quickly increased. But during 4℃and 25℃storage, the soluble solids content, color and the rate of deposition slightly changed. During the storage, soluble xylan content (mainly XOS) and pH did not change and cloud stability firstly decreased and then slightly changed.