Preparation Of Catechin And Its Effect On Wheat Starch Properties And Noodle Quality

My country is the largest producer and consumer of tea.Tea mainly contains polyphenols.Flavanols,mainly catechins,account for 60%to 80%of the total tea polyphenols.(-)-Epigallocatechin gallate(EGCG)has the highest content of catechins and has a variety of biological activities.In recent years,its research has become more extensive and in-depth.At present,there are few research reports on the application of catechins in staple food processing.Therefore,this experiment first extracts and separates catechins from tea leaves,and further separates and purifies EGCG monomers.Secondly,the problem of starch aging,the effects of catechins on the total starch,A starch and B starch and characteristics of wheat were studied.Finally,the effects of catechins on the quality of fresh noodles and frozen cooked noodles were investigated,in order to provide a theoretical basis and technical reference for the development of functional noodles.Firstly,the extraction technology of catechins from tea was determined,and EGCG was separated and purified.The results showed that the optimum extraction process of catechins from tea was optimized by single factor and response surface methodology.The highest extraction rate of catechins was 16.58%when the ratio of liquid to material(m L:g)was 20:1,the extraction temperature was 74?,and the extraction time was 30 min with 30%ethanol.The purity of EGCG was 31.71%after extraction with ethyl acetate,68.51%after silica gel column chromatography and 82.12%after polyamide column chromatography.Finally,the purity of EGCG was 98.78%after C₁₈ reverse column chromatography.Meanwhile,the hardness and elasticity of starch gel increased with the increase of catechin content.In terms of viscosity,with the increase of catechin content,the stickiness of total wheat starch and wheat A starch is increasing.On the contrary,the viscosity of wheat B starch is decreasing,which is related to the gel morphology of wheat B starch.According to the infrared spectrum,no new covalent bond was formed in the simple compound process of three kinds of wheat starch and catechin.It just increases the number of intramolecular hydrogen bonds.Secondly,the effects of catechins(0.5%-1.5%)on wheat starch properties were investigated.DSC results showed that with the increase of catechin content,the initial gelatinization temperature of wheat starch decreased,and the peak temperature,final temperature and enthalpy of gelatinization decreased significantly(p<0.05).RVA test showed that the gelatinization temperature of total starch,a starch and B starch did not change significantly with the increase of catechins,the peak viscosity of total starch and a starch decreased,the peak viscosity of B starch increased,and the low viscosity showed a downward trend.In addition,catechins reduced the retrogradation values of the three starches.In addition,the effects of Catechin on the gel properties of three kinds of wheat starch were investigated.It was found that the hardness and elasticity of the three kinds of starch gels increased with the increase of freeze-thaw cycles.With the increase of catechin content,the hardness and elasticity of starch gels increased significantly(p<0.05),the viscosity of total starch and A starch increased,while the viscosity of B starch decreased.Fourier transform infrared spectroscopy showed that catechin did not form new covalent bonds,but polyphenols and starch formed intramolecular and intermolecular hydrogen bonds.The results showed that the quality of fresh and cooked tea noodles was the best when adding 0.5%catechin.The dry matter loss of fresh noodles added with catechins was higher than that of the blank samples.In the cooking process of noodles,the process of steaming for2 min and then boiling for 1 min was selected,which effectively reduced the cooking loss of frozen cooked noodles and the loss rate of catechins when noodles were re cooked.The effects of catechins on texture,water migration and starch digestibility of frozen cooked noodles were determined after frozen storage at-18?.The results showed that the hardness of frozen cooked noodles added with 0.5%catechins was the highest and the cohesiveness was the lowest.Catechins could effectively slow down water migration and delay the aging and retrogradation of frozen cooked noodles.