Modification,Structural Characterization And Antioxidant And Probiotic Activities Of Hawthorn Pectin

Pectin is a kind of complex acidic polysaccharide,which is widely used in food and pharmaceutical industries.The molecular weight and physicochemical properties of pectin are the main factors affecting its application characteristics and biological activity.The rich content of pectin in hawthorn is an important resource for extracting pectin.Large molecular weight pectin has good functional properties in gel,thickening and emulsification.At the same time,it has been found that pectin modification can change its molecular weight and physicochemical properties,giving pectin new applications and high biological activity.Therefore,appropriate modification of hawthorn pectin can improve its physicochemical properties and biological activity,which is conducive to the development of pectin-related products and broaden the application of pectin.In this project,hawthorn pectin(CK)was extracted from the by-product of processing hawthorn decoction pieces(hawthorn dry debris)and the enzymatic modification process,physicochemical properties,separation,purification and structure analysis of modified pectin and its antioxidative and probiotic activity in vitro were studied.The main study contents and results are as follows:1.Optimization of modification process of hawthorn pectin.With reducing sugar content and intrinsic viscosity as indexes,the optimal modification conditions of pectinase,pectin lyase,pectin methylesterase-?(composite),cellulase and methylesterase-?? were studied by single factor experiments.The optimal conditions for pectinase modification of hawthorn pectin were as follows: p H 3.5,temperature 40?,enzyme dosage 12 U/m L and time 4 h;The optimal conditions for pectin lyase modification of hawthorn pectin were as follows: p H 7.5,temperature 45?,enzyme dosage 65 U/m L and time 4 h;The optimal conditions for pectin methylesterase-?(composite)modification of hawthorn pectin were as follows: p H 4.0,temperature 45?,enzyme dosage 620 U/m L and time 4 h;The optimal conditions for cellulase modification of hawthorn pectin were as follows: p H 4.8,temperature 50 ?,enzyme dosage265 U/m L and time 7 h.2.The properties,structure,antioxidant and probiotic activities of pectinase modified pectin(MPE),pectin lyase modified pectin(MPLE),methylesterase-?(composite)modified pectin(MPME),methylesterase-?? modified pectin(ME)and cellulase modified pectin(MCE)were studied.The results showed that the five modified pectin sample were all low methoxyl pectin.The galacturonic acid(Gal A)content(92.01%)and degradation temperature(135°C)of MPLE were the highest,the particle size of MCE(238.0 nm)was the smallest,and the molecular weight of MPME(3.59 k Da)was the lowest.ME had good emulsifying and gel properties.Infrared spectroscopy(FT-IR)indicated that the enzymatic treatment did not change the primary structure of pectin.Scanning electron micrographs(SEM)showed that the modified pectin with small molecular weight had different degrees of fragments and irregular shapes.In vitro antioxidant and prebiotic experiments showed that the five modified pectin had different degrees of antioxidant and probiotic activities,among which MPE had the best overall activity.3.The physicochemical properties,structures,antioxidative and probiotic activities of three graded modified pectin polysaccharides(MPE-50,MPE-70 and MPE-90)of MPE obtained by alcohol precipitation and fractionation were studied.The results showed that the molecular weight(Mw)of the three graded pectin were: 10.22 k Da(MPE-50),7.30 k Da(MPE-70)and5.70 k Da(MPE-90).FT-IR spectra showed that the three graded pectin had the same functional group types but different contents.Scanning electron micrographs(SEM)showed that the three graded pectin exhibited loose and irregular lamellar structure.MPE-90 had the highest antioxidant and probiotic activities.4.MPE-90 had the highest bioactivity in purified pectin fraction,which were analyzed by methylation and NMR spectroscopy.Twenty-nine derivatives were found and identified in methylation analysis,among which the relative molar ratio of 4-Gal(P)-UA glycosidic bond(35.779%)was the highest.Through NMR spectroscopy combined with methylation analysis,it was determined that there were six sugar residues in the structure of MPE-90,and further confirmed the existence of T-?-L-Araf(1?4)-?-L-Gal Ap(1? structure by HMBC correlation.