Study On Structural And Physicochemical Properties Of Modified Dietary Fiber From Basal Part Of Bamboo Shoot And Its And Application In Yoghurt

Bamboo shoot is a kind of healthy food with high content of dietary fiber.Various studies had proved that bamboo shoot dietary fiber exhibits certain health effects on human body,such as promoting lipid metabolism,controlling body weight and regulating intestinal flora.When bamboo shoot was processed,basal part of bamboo shoot is an unutilized by-product,which is an abundant and low-cost resource for the production of dietary fiber.However,the dietary fibers extracted from basal part of bamboo shoot?BDF?by traditional methods could cause negative influence on food quality when it is added to the fiber-reinforced food due to its low solubility,large fiber particle size and poor degradability,and thus limiting its application in the food industry.Therefore,this study intends to reduce the particle size,and improve the structural and functional properties of BDF by different modification methods,and preliminarily explore the application of modified BDFs in food products.BDF was modified by composite enzymatic method?EBDF?and combined enzymatic hydrolysis-dynamic high-pressure microfluidization?DBDF?,and the changes of structural and functional properties of BDF,EDF and DBDF were analyzed by X diffraction,infrared spectroscopy,nuclear magnetic resonance and adsorption determination.Finally,based on the results of in vitro probiotics effect of BDF,EDF and DBDF,the application potential of the fibers in fiber-enriched yogurt was then explored and evaluated.The main results were as follows:?1?Optimization of modification process of BDFIn order to reduce particle size of dietary fiber,the composite enzymatic modification process of BDF was optimized.The effects of composite enzyme dosage,modification temperature,time and pH values on the particle size were investigated,and the process was optimized by the response surface method,and the optimal modification process as follows:0.20%composite enzyme dosage?cellulase:xylanase=1:1?,temperature of 47?,2.0 h and pH of 5.4.The particle size index D₉₀0 of EBDF was 97.2±0.14?m,while that of DBDF was further decreased to64.3±2.94?m.?2?Effects of modification on structural and functional properties of dietary fibers from basal part of bamboo shootCompared with unmodified BDF,the functional properties of EBDF and DBDF,including water holding capacity,oil holding capacity,swelling power,cation adsorption capacity,cholesterol adsorption capacity,cholate adsorption capacity,viscosity of dietary fiber were significantly enhanced,indicating that modification methods,especially forcombinedenzymatichydrolysis-dynamichigh-pressure microfluidization,could effectively improve the functional properties of bamboo shoot dietary fibre.The thermal stability and viscosity of DBDF were higher than those of EBDF and BDF.The fiber structure of modified EBDF and DBDF became loose,especially the pore structure on the fiber surface of DBDF increased significantly and the fiber presented reticular structure.X-ray diffraction and nuclear magnetic resonance?NMR?results showed that BDF,EBDF and DBDF have typical?type cellulose spectra,and their crystallinities followed the order:DBDF>EBDF>BDF.The results of FTIR spectra showed that some amorphous components of BDF were removed by the modified treatments.?3?Effects of modification on the prebiotic functions of dietary fibers from basal part of bamboo shootThe prebiotic functions of fiber samples were investigated by growth stimulation of bifidobacterium longum and lactobacillus acidophilus in sugar free MRS base medium separately supplemented with same amount?20 mg/mL?of BDF,EBDF,DBDF and inulin as well as glucose.The bacterial number and pH value of the media were measured.The bacterial counts in media with glucose or inulin rapidly increased in the first 24 h or 36 h.After reached the highest points,the bacterial number in the media supplemented with glucose or inulin constantly declined due to the short-supply of carbon source and increased acidity of the media.Comparing with glucose and fermentable inulin,BDF,EBDF and DBDF could not stimulate the bacterial growth in the short time due to their complex chemical structure and limited digestible components in the fibers,which were not easily obtained for the growth of bacteria.However,bamboo shoot dietary fibers could provide bacteria more superficial area to adhere on and constantly provide carbon source during the whole incubation process.After 72 h of incubation,the bacterial counts in culture media added DBDF is highest among all five types of culture medium.There were significant differences in the effects of different carbon sources on the production of short-chain fatty acids by bifidobacterium longum and lactobacillus acidophilus.The addition of glucose and inulin could preferably promote the probiotics to produce lactic acid,acetic acid and propionic acid,while the addition of BDF,EBDF and DBDF was beneficial to the production of butyric acid.Compared with BDF and EBDF,DBDF was the best carbon source for probiotics to produce short chain fatty acids.?4?Application of dietary fibers in fiber-enriched yogurtThe application of dietary fiber in yogurt products could improve the quality and health function of yogurt.The same amount?1%w/w?of BDF,EBDF or DBDF was added into yogurt,with 1%?w/w?of glucose or inulin addition as the controls,the dynamic changes of viscosity,pH value and acidity,as well as the results of sensory analysis were used to investigate the influence of dietary fiber on the quality characteristics of yogurt.The acidity and pH value of yoghurt showed that glucose yoghurt had the highest acidity,followed by inulin yoghurt,and EBDF yoghurt had the lowest acidity among the three dietary fiber samples.Adding dietary fiber could significantly improve the viscosity and water retention of yogurt,and the order from high to low was:DBDF>EBDF>BDF.The sensory analysis of yoghurt showed that dietary fiber could reduce whey precipitation and had no effect on the aroma of yoghurt.However,due to the large fiber particle size of BDF and EBDF,rough taste and the precipitation on certain levels were noticed,which affects the sensory quality of yogurt.Due to the smallest fiber particle size of DBDF,the addition of DBDF in the fiber-enriched yoghurt caused the lowest negative influence on the taste and quality.