Study On Adsorption Of Pancreatic Lipase And Cholesterol By Soluble Dietary Fiber Of Modified Lotus Root Nodes

Lotus node,the non-edible part of lotus root,is the main by-product in the processing of lotus root.With the advances in processing technology,alternative treatments such as micronization have been developed to produce DF-enriched food and non-food products,resulting in the emergence of new and economically viable ways for processing such byproducts.Recent studies have shown that soluble dietary fiber in lotus root nodes has good physicochemical properties and may perform the function of obesity prevention and fat regulation.However,very few studies have been performed so far about the specific mechanism of SDF in adsorbing some functional substances.In this study,the potential mechanism of SDF in adsorbing some functional substances was explored by analyzing its structure and physicochemical properties as well as its adsorption capacity and activity of pancreatic lipase and cholesterol.First,on the basis of previous studies,the structure and properties of SDF1 and SDF2 were studied by scanning electron microscopy,infrared spectroscopy and X-ray diffraction.The relationships between micronization and composition as well as between structure and physicochemical properties were explored by analyzing their microstructure.The results showed that: micronization decreased the relative molecular weight and increased the water solubility and viscosity.The porosity of SDF extracted by micronization increased obviously as indicated by scanning electron microscopy and BET surface area measurement.The shape of the pore was honeycomb-like and the specific surface area increased correspondingly.As a result,the cation exchange performance was improved,and the thermal stability of the modified SDF was enhanced as tested by DSC.The crystallinity of SDF1 extracted by micronization lotus root was higher than that of SDF2 extracted non-modification lotus root,indicating that micronization reduced the symmetry of molecules and increased the disorder,which was mearsured by X-ray diffraction study.Here,the mechanism involved in the adsorption capacity and activity of pancreatic lipase was explored mainly by analyzing the adsorption of pancreaticlipase by SDF under different conditions.The results showed that the adsorption and activity of pancreatic lipase can be affected by SDF,but with a more significant effect from the modified SDF2.SDF1 and SDF2 reached the adsorption equilibrium basically at the same time,but the adsorption capacity varied with the concentrations of pancreatic lipase.The saturation adsorption capacity of SDF1 and SDF2 was 12mg/g and 14 mg/g,respectively.The types of fluorescence quenching,binding sites and binding force between SDF and pancreatic lipase were investigated by fluorescence measurement,and SDF was found to have fluorescence quenching effects on pancreatic lipase.The quenching types of SDF1 and SDF2 were dynamic quenching and complex quenching.The binding sites were about 1 and 1.5,respectively,and the binding force was both Van der Waals and hydrogen bonding.The changes of the secondary structure of pancreatic lipase after the adsorption were investigated by circular dichroism analysis,revealing an obvious a significant decrease in the proportion of beta-folding structure(from 87.2 to 74.8% and 65.8%)after SDF1 and SDF2 treatment.A comparison of the secondary changes of pancreatic lipase caused by the addition of SDF1 and SDF2 showed the decrease in pancreatic lipase activity is mainly due to the elongation of the ?-sheet structure.The main adsorption group was determined by carboxymethyl and hydroxypropyl,and the hydroxyl group was found to play a major role in the adsorption of SDF on pancreatic lipase.Finally,the adsorption capacity of SDF on cholesterol was studied,and it was found to decrease gradually until the minimum,followed by a gradual increase with the increase of SDF dosage,probably due to the surface adsorption,pore adsorption and chemical adsorption of cholesterol by SDF.The adsorption of SDF on cholesterol increased along within a certain time range,and gradually reached the equilibrium.The maximum adsorption capacity of cholesterol was 47.8 mg/g and 48.3 mg/g for SDF1 and SDF2,respectively.Generally,SDF can adsorb a large amount of cholesterol quickly via monolayer adsorption,but after reaching the maximum adsorption,the absorption amount of cholesterol did not increase significantly along with the decrease of cholesterol concentration.Freundlich model formula fits better.Freundlich model characterizes multi-layer adsorption,which indicated that the adsorption of cholesterol by SDF1 and SDF2 was multi-layer adsorption.The isotherm fitting results showed that the adsorption of cholesterol by SDF includes both physical adsorption and chemical adsorption.In the process of physical adsorption,cholesterol quickly forms the monolayer adsorption on the surface of SDF,followed by the formation of the multilayer adsorption via intermolecular attraction.Adsorption is a spontaneous,endothermic process,and warming is beneficial to the process of adsorption.The chemical adsorption of cholesterol by SDF is mainly attributed to the presence of many active groups on its surface,which can directly chelate cholesterol molecules.The X-ray photoelectron spectroscopy analysis revealed obvious changes in the peak shape and intensity of carbon and oxygen atoms after the adsorption of cholesterol by SDF-1 and SDF-2,indicating the potential variations in the content and chemical state of carbon and oxygen atoms,probably due to the effect of adsorption on the number of carbon and oxygen atoms and the polarization conditions around them.The results of carboxymethyl and hydroxypropyl demonstrated that the adsorption effect of carboxyl groups was the main adsorption site.