Extraction Of Soluble Dietary Fiber From Grapefruit Peel By Microwave Assisted Modification And The Effect Of Its Addition On Bread Quality

In this study,the optimal conditions for microwave-modified extraction of soluble dietary fiber(SDF)from grapefruit peel were optimized by response surface to obtain the maximum yield of SDF.Then combined the optimized microwave conditions with sodium hydroxide,cellulase and ultrasound.Using the microwave-sodium hydroxide treatment(MST),microwave-enzymatic treatment(MET)and microwave-ultrasonic treatment(MUT)to modify grapefruit peel,and the structural and functional properties of extracted SDF,named as MST-SDF,MET-SDF and MUT-SDF,were investigated respectively.Meanwhile,compared modified SDF with the without treatment grapefruit peel SDF(WT-SDF)and the pure microwave treatment grapefruit peel SDF(PMT-SDF)to study the effect of modification.Finally,the extracted grapefruit peel SDFs are added to the bread to obtain WT-SDF bread(WB),PMT-SDF bread(MB),MST-SDF bread(SB),MET-SDF bread(EB)and MUT-SDF bread(UB).Through comparison with the blank control,explore its structural properties,functional properties,in vitro digestion properties to develop a more flavorful and low glucose release rate bread.In order to further improve the utilization rate and economic value of grapefruit peel.The main findings are as follows:(1)Based on the results of single factor experiment,the conditions for microwave modification was optimized by the Box-Behnken response surface method to extract SDF from grapefruit peel.The effects of microwave time,microwave temperature,and microwave power on the yield of grapefruit peel SDF were investigated and the best processing conditions are: microwave temperature80 °C,microwave time 40 min,microwave power 500 W.(2)After the microwave combined modification of grapefruit peel SDF,the MST-SDF,MET-SDF and MUT-SDF showed a more complex and loose structure.Moreover,they possessed higher molecular weight,crystallinity and thermal stability,and more diverse monosaccharide composition.In addition,the yield of modified grapefruit peel SDF increased significantly,and also the functional properties.Among them,the MST has the worst improvement effect,and MUT has the best.The MUT-SDF not only exhibit superior structural properties,but also possess the strongest binding ability of water,oil,cholesterol,glucose and nitrite ions.(3)Adding microwave combined treated grapefruit peel SDF to bread can make the number of holes in the bread more abundant and the structure more stable.In addition,it could improve the taste and texture of the bread to a certain extent,giving the bread longer shelf life and special aroma,better taste and higher acceptance.Moreover,adding microwave combined treated grapefruit peel SDF to bread can make bread possess higher functional properties.Not only improved the water holding capacity(WHC),cholesterol adsorption capacity(CAC),and nitrite ion adsorption capacity(NIAC)of bread,but also it reduced the glucose release rate of bread.In the SDF breads,UB has ideal hardness and internal structure,and its thermal stability is significantly higher than other samples.Meanwhile,in the functional properties,it has the strongest ability to inhibit the release rate of glucose,and the highest overall acceptance,WHC,CAC,and NIAC.The research results can provide a reference for the development of functional foods that reduce the amount of glucose released,and provide a new method for promoting the use of grapefruit peel.