Fractionation,Structural Characterization And Application Of Cell Wall Components In Chinese Quince Fruits

Chinese quince(Chaenomeles sinensis)belongs to the Rose family.Due to their properties of strong acidity,astringency and woody hard flesh,Chinese quince fruits are unpalatable raw and only consumed in the form of fruit liquor,jam,jelly,decoction and candied fruit.The hard woodiness of the flesh is due to the high amount of lignin in the cell wall of the fruits.In addition,Chinese quince fruits are also rich in cell wall polysaccharides,such as pectin.Lignin is linked with these cell wall polysaccharides,such as hemicellulose and pectin,to form lignin carbohydrate complex.These natural macromolecules have various functional properties,e.g.lignin having antioxidant activity and ultraviolet resistance,lignin carbohydrate complex having antiviral and antitumor activities,pectic polysaccharide has emulsifying,gel-forming and thickening abilities.So they can be widely used in food,medicine,chemical and other fields.How to achieve high-efficiency separation and purification of these natural macromolecules is of great significance for improving the high value utilization of Chinese quince fruits.The researches about the lignin,lignin carbohydrate complex,cell wall polysaccharide(pectin)in Chinese quince fruits,have rarely been reported.In this paper,basing on the specificity of the fruit ingredients,fractionation,structural characterization and application of lignin,lignin carbohydrate complex and pectin in Chinese quince fruits have been studied.These studies will provide theoretical and technical supports for isolation and deep processing utilization of the cell wall components in Chinese quince fruits.The main research contents and conclusions are as follows:1.Three pretreatment processes were evaluated for their effects on the structural features and antioxidant activities of lignins extracted by the acetosolv process from the fruit of Chinese quince.The three pretreatments included dephenolization,sugar removal,and multiple processes(a combination of both dephenolization and sugar removal).The results showed that after sugar removal pretreatment,the carbohydrate content,the molecular weight and S/G value of the lignin fractions decreased.However,after dephenolization pretreatment,the carbohydrate content and the molecular weight of the lignin fractions increased.After sugar removal and dephenolization,there were increases in the temperatures corresponding to the maximal rate of decomposition(DTGmax)in all lignin fractions.The radical scavenging index of lignin after sugar removal pretreatment was higher compared to other pretreatments and no treatment.The results of these tests showed that sugar removal,as a pretreatment,enhanced lignin extraction,yielding pure and highly functional lignins.Additionally,dephenolization or multiple process were beneficial to the acquisition of macromolecular lignins.All the results provided references for the biorefinery of biomass rich in polyphenol and sugar compounds.2.Structural characteristics of lignin isolated from Chinese quince fruits by multienzymatic hydrolytic pretreatments were studied.The structures of these multi-enzyme mixture lignin(EML)fractions were analyzed and compared with conventional cellulolytic enzyme lignin(CEL).EML fractions are structurally similar to CEL fractions except for an increased S/G ratio,greater number of ?-O-4 linkages,higher average molecular weight and decreased thermal stability.The EML-2 fraction in particular seemed most representative of the lignins isolated,and it exhibited the highest antioxidant activity in comparison with CEL and other EML fractions.3.The structure of lignin-carbohydrate complexes(LCCs)from Chinese quince fruits were studied.Three different methods of fractioning,namely,milled wood lignin(MWL),LCC extracted from crude MWL with acetic acid(LCC-AcOH),and Bjorkman LCC were used for the isolation of LCCs from the mesocarp(MS)and near the endocarp(NE)of Chinese quince fruits.The MWL and LCC fractions were characterized by carbohydrate composition analysis,SEC,FT-IR,Py-GC/MS,thermal analysis and 2D HSQC NMR.Notably,large amounts of arabinose and galactose remained in the Bj?rkman LCC fractions suggesting a chemical bond between the lignin and pectin.MWL and LCC-AcOH fractions showed better thermal stability than Bj?rkman LCC fractions.The structure of MS lignin was similar to that of NE lignin;however,fractions from different fractionation methods revealed differences.The MWL fractions were rich in benzyl ether and ?-ester linkages,while the Bj?rkman LCC fractions contained phenyl glycoside and ?-ester linkages,and the LCC-AcOH fractions contained phenyl glycoside and benzyl ether linkages.These findings are helpful in understanding the nature of lignin and LCC in Chinese quince fruits and provide a theoretical support for their potential application.4.Composition and structural features of cell wall polysaccharide from Chinese quince fruits were investigated.Three pectin fractions and two hemicellulose fractions,including water soluble pectin(WSP),chelator-soluble pectin(CSP),sodium carbonate-soluble pectin(NSP),1 mol/L KOH soluble hemicellulose(KSH-1)and 4 mol/L KOH soluble hemicellulose(KSH-2),were isolated from Chinese quince fruits.The five fractions exhibited structural and compositional variation.The results showed NSP represented the most abundant cell wall polysaccharide fraction in the fruit.The cell wall pectin fractions WSP and NSP had low degree of methyl esterification(DE 31.7%-42.4%).WSP fraction had the highest thermal stability among the five fractions.The chain lengths of five cell wall polysaccharide fractions ranged from 19.4 nm to 121.4 nm.The highest molecular weight of CSP resulted in its highest viscosity in solution.Among the five fractions,CSP has the highest DPPH radical scavenging activities while KSH-1 has the highest reducing power.5.The effects of pretreatment-drying methods on structure and properties of pectins extracted from Chinese quince fruits were studied.Sun-drying,lyophilization and a new drying method subcritical dimethyl ether(DME)dewatering technology were applied for drying of the fruits.Then the sun-dried,lyophilized,subcritical DME dewatered fruits as well as the fresh fruits,were used to extract pectins giving rise to fractions SP,LP,DP and FP,respectively.Among the pectin samples,LP had the highest yield(10.49%),the highest molar mass(65120 g/mol),the highest water holding capacity(WHC)value,but DP had the highest degree of esterification(72.95%),the lowest molar mass(45860 g/mol),the highest oil holding capacity(OHC)value.The four pectin samples had different surface morphology.LP was most thermally stable among the pectin samples.The four pectin solution at the concentration of 2.5% all presented non-Newtonian pseudoplastic behavior.In addition,LP exhibited higher DPPH scavenging activity and reducing power than FP,SP and DP.