Modification Of Dietary Fiber From Millet Bran And Its Application In Yogurt

Millet bran is a by-product of millet processing and dehulling,rich in nutrients,especially dietary fiber(DF)content accounts for more than 18%of millet bran mass.DF is the most typical functional substance in cereals,but the current research is mainly focused on the processing by-products of wheat,rice,oats and corn.Most of the millet bran is used as livestock feed directly or after rough processing,and the added value of the product is very low.Modification treatment can significantly increase the soluble dietary fiber(SDF)yield and effectively improve the physicochemical and functional properties of dietary fiber,however,there are few studies on modified millet bran dietary fiber.In the previous pre-experiment,we analyzed and compared the yield of SDF modified by high temperature,cellulase,xylanase,α-amylase and protease,and found that the yield of SDF modified by high temperature and the combination of cellulase and xylanase was higher.Therefore,this study was conducted to improve the yield of SDF and analyze its structural and functional properties through high temperature and high temperature-combined enzyme modification,in order to provide ideas for the comprehensive utilization of millet and the preparation of soluble dietary fiber from millet bran and the development of functional foods.The main research results are as follows.(1)Optimization of the modification process of dietary fiber from millet branThe high-temperature-composite enzyme modification process of dietary fiber from millet bran was optimized with the objective of improving the SDF yield.The effects of compound enzyme addition,compound enzyme ratio,enzymatic digestion temperature and time on SDF were investigated,and the high temperature-composite enzyme modification process was optimized by the response surface method and modified according to the actual operation:the ratio of compound enzyme(xylanase:cellulase)was 2:1,the compound enzyme addition amount was 2%,the enzymatic digestion temperature was 50℃,and the enzymatic digestion time was 1.50 h.After modification under these conditions,the yield of soluble dietary fiber(SDF)from millet bran was 17.27 ± 1.57%.(2)Effect of modification treatment on the structural and functional properties of dietary fiber from millet branCompared with DF,the physicochemical and functional properties of modified TDF and T-EDF,including water-holding power,oil-holding power,swelling power,swelling property,cation adsorption capacity,cholesterol adsorption capacity and bile acid salt adsorption capacity,were significantly enhanced,indicating that the modified treatment could effectively improve the functional properties of dietary fibers.The study on the monosaccharide composition of dietary fibers showed that there were significant differences(P<0.05)between the contents of individual monosaccharides in DF before and after modification,in which the glucose content in defatted millet bran was higher than xylose,while the highest xylose content was found in DF,TDF,and T-EDF;it could be observed by environmental scanning electron microscopy that the fiber structures of TDF and T-EDF after modification treatment became looser,especially T-EDF.The results of X diffraction showed that DF,TDF and T-EDF showed that typical type Ⅰ cellulose spectra,and the crystallinity of T-EDF>TDF>DF was ranked from largest to smallest.(3)Fortification of coagulated yogurt by high temperature-composite enzyme modified dietary fiberThe shear stress,viscosity,consistency index and pH value of yogurt in the T-EDF group were higher than those in the control group,i.e.,the yogurt with T-EDF was more stable during the storage period of 15 days;the results of sensory analysis of yogurt showed that the addition of dietary fiber reduced whey precipitation and did not affect the aroma of yogurt The results of sensory analysis showed that the addition of dietary fiber reduced the precipitation of whey and did not affect the aroma of yogurt;38 volatile flavor compounds were detected in the two groups of yogurt samples,including 4 ketones,8 aldehydes,5 alcohols,9 esters and 12 other compounds,by searching compounds in the software GC × IMS Library Search.The addition of dietary fiber to yogurt can mainly promote the formation of aldehydes,alcohols and esters flavor substances in yogurt.Therefore,these results suggest that T-EDF may be an important component for improving yogurt quality.The study may provide theoretical guidance for the development of functional foods rich in dietary fiber.