Preparation Of EGCG And Its Effect On Gelatinization And Retrogradation Of Wheat Starch

In this study,green tea,as raw material,was extracted by water to make green tea water-extract(GTWE).Then,GTWE was absorpted by LP-8 macroporous resin and eluted properly to make tea polyphenols with high propertion of ester catechins.Finally,high purity of EGCG monomer was separated and purified from this tea polyphenols by medium pressure liquid chromatography(MPLC).EGCG and wheat starch were mixed well.The effects of EGCG on gelatinization and retrogradation of wheat starch and possible interactions of EGCG with wheat starch was observed and analyzed.LP-8 macroporous resin has specific adsorption capacity for tea polyphenols,and can effectively remove caffeine from GTWE.Adsorption flow rate and sample concentration had an effect on the adsorption,and the optimum adsorption conditions were the elution flow rate of 1Bv/h,the concentration of 30 mg/m L.After gradient elution and in order to improve the elution efficiency,the elution conditions were optimized.The optimized elution conditions were using 35% ethanol and 70% ethanol,which were carried out to obtain tea polyphenols with high propertion of ester catechins.Among them,the purity of tea polyphenols was 82.41%,the purity of ester-type catechins was 63.21%,the recovery was 89.33%;the purity of EGCG was 49.87% and the recovery was 92.10%.The high-purity EGCG monomers were obtained by medium-pressure liquid chromatography(MPLC).Optimized separation process parameters were 4.0g loading amount with 20% ethanol elution and 30 m L/min elution flow rate.The purity of EGCG reached 95.22% and the recovery was 95.03%.From tea raw material to EGCG,macroporous resin and medium-pressure preparative chromatography are used in series.Water and ethanol were used as main solvents.The whole process was continuous and green preparation,and have the prospect of industrialized application and production.EGCG could affect the gelatinization and retrogradation of wheat starch.EGCG was mixed with wheat starch at the dosage of 1.0%(w: w).Compared with the control(no EGCG added),the peak viscosity,viscosity,final viscosity and setback value of wheat starch decreased,which were observed by rapid viscosity analyzer(RVA).However,pasting temperature had no change.The peak time decreased,indicating that EGCG may shorten the gelatinization peak time of wheat starch.EGCG-wheat starch complex formed after gelatinization were stored for 0,12,24 h at 4?.Observations by X-ray diffraction,thermogravimetric analysis,particle size analysis revealed that the complex had less crystallinity,weaker peak shape change,lower thermal stability than the control,indicating that EGCG could delay the retrogradation of wheat starch.Observations by Fourier transform infrared spectroscopy(FT-IR)and Raman spectroscopy showed that the hydrogen bonding in the complex was stronger than the control,which means there may exist hydrogen bond between EGCG and wheat starch chains.Based on the hydrogen-bonding interaction,EGCG could interfere structural changes of starch chains during gelatinization and retrogradation.