Preparation Of Modified Citrus Pectin Based On Photo-catalytic Hydrogen Peroxide Oxidation Reaction And Its Structure And Properties

Modified Citrus Pectin?MCP?was proved to show the functions in decreasing both incidence of cancer and cancer metastasis,as well as the antioxidant and immune-mediation activities,which suggested its potentials to be developed into novel ingredients of functional food and the active components for anti-cancer drugs.In this thesis,preparation of MCP series derivatives was conducted by means of UV-photo catalyzed hydrogen peroxide oxidation reaction?UV+H₂O₂?.The influence factors of MCP preparation,the structure of the obtained products,the possible mechanism,the rheology and the biological activity was studied.Main contents and results are as following:?1?Development of the process for MCP preparation by UV+H₂O₂ and its mechanism.The process route was determined as following:firstly the raw material citrus pectin was dispersed in DI water and followed by ultrasound pretreatment,pH adjustment,H₂O₂ addition,UV irradiation for reaction,UV removal to stop reaction,neutralization,dialysis,concentration,recycling by ethanol precipitation and dry to obtain the final product MCP_UV+H₂O₂.According to the results from the single factor study,the loading amount of H₂O₂ determined the efficiency of the reaction and the degree of the modification on CP as well.Additionally,the difference of the pH values of the reaction solution resulted in a significant difference in the degree of esterification among the final products.The mechanism of UV+H₂O₂ reaction for MCP preparation could be concluded as an oxidation degradation reaction produced by hydroxyl radicals.At acidic or neutral conditions,the degradation occurred mainly at the reducing end of CP,whereas at the basic condition,saponification reaction and?-elimination reaction happened as well.?2?Structural characterization and rheological property study.Results from GPC?FT-IR?¹HNMR indicated that the weight-average molecular weight of MCP series varied from 1223kDa to about 50 kDa with a complete structure of pectin fragment.Rheology study shows that MCP solution changed from a non-Newtonian fluid to a Newtonian one with the decreasing of the molecular weight of MCP.Studies on the gelling properties of MCP indicated that the addition of both sucrose and Ca²⁺to MCP_pH4 contributed to the occurring of gel,which has a mechanical strength in a direct proportion with its molecular weight.Meanwhile the mechanical strength of the gel from MCP_pH12 and Ca²⁺complex was much higher than that of unmodified CP,which was highly related with the molecular weight and the degree of esterification.?3?Preparation of low molecular weight modified citrus pectin?LMW-MCP?by combined UV+H₂O₂ and enzymatic degradation?UV+H₂O₂+En?.The optimized condition enzymatic step was as following:50?,pH 3.5 and pectinase dose of 1.4%for 16 h.The resulted LMW-MCP product varied in the range of 50 kDa⁴ k Da with a yield of no less than 50%.SEM observation indicated that LMW-MCP appeared as irregular small fragments instead of an aggregation of large molecules.?4?Purification of MCP fragments and a preliminary exploration on the binding capacity with lectins.The crude MCP products prepared by UV+H₂O₂ and UV+H₂O₂+En were purified by means of gel chromatography,resulting in 8 MCP fragments with molecular weight range of 5 kDa to 300 kDa.An in vitro system consisting of chicken blood red cell and Ricinus communis agglutinin?RCA?was used for evaluation of the binding between MCP and RCA.Results indicated that the minimum inhibition concentration of RCA was 6.25?g/m L.The binding ability of MCP for RCA was found to highly related with the molecular weight of MCP fragments and the one with an average molecular weight of 6.1 kDa showed the highest binding capacity with RCA among all the tested samples with MIC value 25±3.0?g/m L.Such a result suggested that this MCP fragments possessed the potential of having anti-cancer and immune-mediation activities.