A Study On Extraction And Characterization Of Pectin Obtained By Subcritical Water From Pomace

In recent years, as the flourishing of the fruit juice industry in China, the resourceutilization of pomace became an important aspect which would limit the development of thewhole industry. As one of the most important component of pomace, pectin was widely usedin food industry, thus the pectin extraction would be one of the most effective way for theutilization of pomace. Acid extraction is the general method for commercial pectin, however,serious pollutions arised from the acidic waste emission.As a new environmental friendly extraction method, the subcritical water extractionattracts much attention, because only water was used in the extraction process without anychemical reagent addition. In our research, subcritical water was used to extract pectin fromapple pomace and citrus peel. The response surface method was used to optimize theextraction process conditions for maximum pectin yield. Thereafter, comprehensiveinvestigation of the extracted pectin was done. The results of our study were as follows:1. The process of pectin extraction by subcritical water from pomace was established andthe process conditions were optimized by the response suface methodology. The optimumlevels of the parameters were obtained as follows: extraction temperature138.8℃, extractiontime5.25min, S:W ratio1:13.95. The average pectin yield of triple validating experiment atoptimal conditions was17.55%, which was approximately equal to calculated17.76%pectinyield according to the regression model, it did not have significant difference betweenexperiment value and theoretical value(P>0.05), which indicated that the regression modelwas proper and accurate.2. Characterization of the pectin extracted under optimal conditions from apple pomace:The galacturonic acid content and DE value of the optimal apple pomace pectin(OAP) were48.20%and60.23%. Compared with commercial pectin from apple pomace(CAP), due to therelatively higher extraction temperature, the content of neutral sugar and ash of OAP washigher, while it was lower of the content of galacturonic acid and protein, molecular weightand DE value. As the similarity of chemical composition, the OAP and CAP had similar and typical FTIR spectra of pectin. For the lower galacturonic acid content and DE value, theendothermic transition temperature and fusion heat of OAP were lower than CAP according toDSC analysis. The OAP solution belonged to non-Newton pseudoplastic fluid, it also showedmore stronger shear thinning characteristics than CAP for its lower molecular weight.Meanwhile, in the processing of dynamic frequency scanning, the storage modulus (G′)increased higher than the loss modulus (G′′) with the increasing of scanning frequency, whichindicated that the elastic dominates in the properties of the fluid. As the gel properties of theOAP were superior to its viscosity properties, so OAP was more suitable to use as a gellingagent, rather than a thickener agent. For the special physicochemical properties, such assmaller molecular weight, DE value, better solubility and so on, OAP showed more effectivein vitro antioxidant capability, inducing apoptosis of Caco-2cell and inhibitory effect on theproliferation of HT-29than CAP. Moreover, as a natural polysaccharide obtained from foodraw material, OAP could be widely used in food and pharmaceutical industries for its safty.3. The yield of citrus peel pectin(CPP,19.21～21.95%) and apple pomace pectin(APP,10.05～16.68%) extracted by subcritical water were relatively higher and the properties ofpectin could be considerably affected by subcritical water extraction temperature and thesource of pectin. The purity of APP decreased with the increasing of extraction temperature,the lower galacturonic acid content and higher neutral sugar content of APP might be causedby the higher extraction temperature which led to the mixture of co-extracts such ashemicelluloses and cellulose. However, this phenomenon was not observed in CPP extractionfor its higher content of organic acid in citrus peel. The FTIR spectra indicated that CPP andAPP had similar chemical composition. As shown in the results of DSC assay, theendothermic property of pectin was affected by extraction temperature while the exothermicproperty of pectin was only affected by its constituents and raw materials. For the random coilof polysaccharide, all the samples exhibited similar shear-thinning properties. Moreover, theelastic dominates in the properties of the fluid (G′> G′′) for the lower molecular weight. Thegel properties of CPP were better than APP, which affected by molecular weight, DE value,and other physiochemical properties. Moreover, based on the special physiochemicalproperties, such as lower molecular weight and special composition of neutral sugar, bothCPP and APP scavenged more than60%DPPH radical and80%ABTS radical in vitro，obviously induced apoptosis of Caco-2cell and inhibited proliferation inhibition rates ofcolon cancer cell HT-29for76.45%and45.23%respectively.