Extraction And Modification Of Dietary Fiber From Sugar Beet Pulp And Its Related Mechanism

Sugar beet pulp (SBP), a byproduct of sugar beet engineering, contains dietary fiber suchas pectin and cellulose, which is cosidered as irreplaceable beneficial nutrients with specicalphysiological functions. However, it is still underutilized today. In order to fully utilize SBPsource and promote healthy and sustainable development of China's sugar engineering, themethods of extracting pectin from beet pulp, modification of pectin with pulsed electric fieldand arachidic anhydrate, homogeneous derivatization of cellulose in ionic liquids and itsrelated structure and mechanism analysis were studied in this thesis.The methods of organic acid, ultrasound and pressure were used to extract pectin fromSBP. The results indicated that the pectins obtained by citric acid, maleic acid and lactic acidwere different in yield and galacturonic acid (GalA) content, respectively. The discrepanciesof pectin yields and GalA content extracted with the methods were not only affected by theirorganic feature but also by their relatively strong or weak nature. The optimal yield (17.1%)and GalA content (78%) were obtained at pH1.5,85oC for2h with critic acid as extractant.Box-Behnken design and response surface analysis were applied in ultrasonic method basedon single factor experiment. Results indicated that the highest yield of6.3%and GalA contentof71%were obtained at pH1.5for45min with ultrasonic power of900W. Twosecond-order equations were caculated, which could be used for predicting the quality ofpectin. In additon, the optimal conditons of pressure method had also been studied. Themaximal yield and GalA content were22.5%and65%, respectively, with the optimalextraction conditions of20Mpa presusre for90min at160oC.The composition and rheological properties of SBP pectin extracted by three mehtodswere studied in this section. The results indicated that there were significantly difference inyield, carbohydrate content, GalA content and molecular weights of pectin. The pectinextracted from organic acid method has a better yield, and its carbohydrate content andgalacturonic acid were the highest, but its molecular weights were relatively low. There wereno significant difference in degree of esterification (DE) between ultrasonic method andpressure method, both of them had higher DE than organic method. The rheologicalproperties of pectin showed that the viscosity of pectin increased with increasing concentration, and decreased with increasing shear rate. The increase of temperature, pHvalue and standing time reduced the viscosity of the pectin, but an appropriate increase in ionconcentration and carbohydrate concentration would enable the viscosity significantlyincreased.The modification of pectin induced by pulsed electric field (PEF) was studied in thissection. Experimental parameters including electric field intensity (18-30kV/cm) and pulsetime (806-2418μs) were used, and the physicochemical properties of PEF-treated pecitn wereevaluated by various instrumental techniques such as, X-ray diffraction patterns, Dynamiclight scattering spectra and FT-IR spectra. The process of pectin degradation was deduced byBuckingham theorem. The results showed that crystalline regions of pectin were destroyedafter being treated with PEF, and the DE, molecular weight and particle size of pectindecreased with the increase of electric field intensity and pulse time. The process of pectindegradation could be evaluated by two obtained simulation models. Results revealed that PEFtechnology is an effective method to obtain the pectins with different molecular-weights andDEs, and get a desired production in food application.The solvent-free modification of SBP pectin with arachidic anhydride were studied inthis section. The parameters included reaction temperature (130-170oC), reaction time (20-60min),anhydride usage (0.5:1-2:1),catalysis usage (0.05-0.15%) and electric intensity (18-30kV/cm). The results showed that pectin-arachates were prepared in one-step solvent-freemodification. The PEF pretreatment had a favourable effect on this reaction, and the weightpercent gain (WI) of pectin derivatives increased with increasing temperature, reaction time,anhydride usage and catalysis usage. However, the WI decreased when temperaute was over160oC. Evidence of pectin modification was provided by FT-IR spectra, X-ray diffractionpatterns and1H Nuclear magnetic resonance (NMR) spectra. Thermal gravimetric analysis(TGA) of modified pectin indicated a higher thermal stability than untreated pectin.Cellulose glutarates were synthesized from beet pulp cellulose and glutaric anhydride inionic liquid (IL)1-butyl-3-methylimidazolium chloride assisted by ultrasound. Parametersinvestigated included ultrasound time, temperature, the molar ratio of glutaricanhydride/anhydroglucose units in cellulose (MRO), and reaction time. The cellulose derivatives were characterized by FT-IR spectra, solid-state CP/MAS13C NMR spectra andTGA. The results showed that the synergy of the combined use of ultrasound and IL hadsuccessfully enhanced the degree of substitution of cellulose glutarates under theexperimental conditions of the present study, and its DS increased with the increment ofultrasond time (from10to40min), temperature (from90to110oC), the MRO in a range from2:1to6:1and reaction time (from20to120min). Besides, the modified cellulose showedlower thermal stability than native cellulose.The stability of a double emulsion made from SBP pectin and Bovine Serum Albuminwas evaluated in the present research. The results showed that the cross-linked stucture wasformed between pectin molecules after peroxidase and hydrogen peroxide added. The optimalconditions of pectin modification were enzyme dosage of200U/g, concentration of hydrogenperoxide0.02%, reaction temperature of40oC and the reaction time of120min. With theconcentration of modified pectin increased, the charge absolute value, interfacial tension andof double emulsion increased, indicating the stability of double emulsion increased. Thedouble emulsion made from modified pectin and protein had a better stability in neutral pHwhile relative unstable in acid pH conditions.