| Soluble dietary fiber(SDF)plays important role in cutting down the glycemic reaction and plasma cholesterol,immunomodulatory activity and reducing the risk of angio cardiopathy.In addition,SDF has a higher capacity to form gels and act as an emulsifier,enabling it to be readily incorporated into food products.The content of SDF in defatted rice bran(DRB)dietary fiber is relatively low,so it is particularly important to use simple and effective modification methods to transform the soluble dietary fiber(IDF)into SDF and obtain high-yield SDF.The purpose of this study was to formulate the optimal Trichoderma viride fermentation conditions via RSM,aiming to obtain the highest yield of SDF from DRB,and to explore the structural and functional characteristics of SDF and its impact on glucose intestinal absorption and transport.At the same time,different proportions of fermentable soluble dietary fiber(F-SDF)were added into flour to make biscuits.The effects of F-SDF on the physical properties and starch digestion characteristics of biscuits were studied to provide theoretical and practical basis for the development of functional biscuits.The main research contents and results of this topic are as follows:(1)The best fermentation conditions for extracting F-SDF were determined by RSM.The yield of F-SDF was significantly increased from 10.5(w/w,%)to 33.4(w/w,%)under the optimal conditions(inoculum size=10%,pH=5.8 and time=41h).(2)The differences of physicochemical properties and functional characteristics between soluble dietary fiber(B-SDF)and F-SDF were compared.Fourier transform infrared spectroscopy(FTIR)demonstrated that both B-SDF and F-SDF had typical characteristics of the infrared spectrum of polysaccharides,and the functional groups of B-SDF and F-SDF are basically similar;X-ray diffraction(XRD)revealed they were mainly substances of amorphous structure;In addition,the scanning electron microscope(SEM)observed that F-SDF showed looser structure than B-SDF,and the specific surface area of F-SDF increased;High performance anion exchange chromatography(HPAEC)analysis showed that fermentation increased the monosaccharide component of SDF(glucuronic acid),and changed the proportion of SDF monosaccharide composition.The analysis of high-performance gel permeation chromatography(HPGPC)proved that two new components in F-SDF were due to IDF conversion during fermentation.At the same time,the results of thermogravimetric analysis showed that F-SDF is more stable when the temperature is less than 200℃.Trichoderma viride fermentation increased the solubility,water holding capacity,oil holding capacity and cholesterol absorption capacity of SDF,but decreased the nitrite removal capacity slightly.The increase of these functional characteristics is more conducive to the metabolic regulation of SDF in the intestine.(3)To investigate the effect of F-SDF on glucose absorption and transport in the small intestine and to ascertain its mechanism of action.F-SDF could delay the absorption and transport of glucose in the small intestine possibly by inhibiting α-glucosidase activity,decreasing the expression of glucose transporter proteins such as SGLT-1,GLUT-2 and Na+-K+-ATPase in intestinal epithelial cells,inhibiting carbohydrate hydrolysis,and occupying glucose absorption sites,and ultimately reducing postprandial hyperglycemia.(4)To explore the effect of F-SDF on the Physical quality and the in vitro starch digestibility of dough and biscuits.Texture analysis showed that the hardness,gumminess and chewiness of biscuit dough increased with the increase of F-SDF,while the springiness,cohesiveness and resilience decreased with the increase of F-SDF.Rheological analysis shows that as the F-SDF content increased,a decrease in and an increase in G" were observed,and the increase of F-SDF made the tanδ of the dough showing an upward trend.These results indicated that F-SDF could increase the viscous ratio of dough system and increase the fluidity of dough.The addition of F-SDF reduced the hardness,springiness,cohesiveness,gumminess,chewiness and resilience of the biscuits.In addition,F-SDF hindered the formation of the gluten network structure in the biscuits,and reduced the area of the crystallization zone.At the same time,F-SDF could capture the moisture in dough and change the water distribution in biscuit.Sensory evaluation results showed that the biscuits with 6%F-SDF had the highest acceptability.In addition,F-SDF leads to a significant reduction in the predicted glycemic index(pGI)of biscuits,and could exhibit potential to decrease the postprandial blood glucose level resulted by biscuit. |
