| Glutamine peptides are defined as bioactive peptides containing glutamine, which aresteady alternatives of glutamine monomers. The glutamine peptides can not only maintainthe physiological features of glutamine, but also overcome the shortcomings of free glutamine,like unstability, so as to improve the solubility, creating the possibility for the supply andapplication of glutamine. This paper studied in selecting the best raw material, best proteaseand best enzymatic hydrolysis system. It also researched the enzymatic activity of Alcalase inethanol solution. In addition, the glutamine peptides prepared under optimum conditions wereinvestigated for physico-chemical properties and antioxidant activity in vitro after theultrafiltration grading and macroporous resin desalting.After studying the relationship between glutamine content and amide nitrogen content,these two indexes showed a good linear relationship. So the amide nitrogen content, whichwas easier and more time-saving, would be the main index when preparingglutamine-rich peptides.Firstly, the selections of best raw material, best protease and best enzymatic hydrolysissystem were investigated. According to the protein content, degree of hydrolysis, peptidescontent and amide nitrogen content, the gluten was better than glutenin and gliadin in allindexes, and Alcalase was better than Neutral protease and Flavor protease in the other threeindexes except degree of hydrolysis. So the gluten and Alcalase were selected as best rawmaterial and best protease. Moreover, the degree of hydrolysis of gluten hydrolyzing inethanol system was not so good as in aqueous system, but the protein content, amide nitrogencontent and peptides content were higher by10%-16%,1%-7.5%and3%-13%respectively.After comparing different types of hydrolysis in ethanol system, the ethanol system of singleconcentration was the best enzymatic hydrolysis system.Secondly, the enzymatic properties and stability of Alcalase in ethanol solution wereinvestigated. The optimum temperatures of Alcalase in30%and50%ethanol solution wereboth45℃, lower than the ones in aqueous solution (50℃-55℃) by5℃-10℃. The optimumpHs were both10-11, very close to those in aqueous solution. The effects of temperature andethanol concentration on Alcalase’s stability were greater than pH. According to inactivationkinetics, with the ethanol concentration raised from30%to60%, the deactivation rateconstant k increased by17times, activation energy E0decreased by7310J, half-life t1/2shortened by13times. All these indicated that the stability of Alcalase declined rapidly.After that, the optimum preparing conditions for enzymatic hydrolysis in ethanolsolution were investigated. The odd-factor and orthogonal experiments determined that, whenethanol concentration40%, temperature47.5℃, substrate concentration14%, the amount ofenzyme7000U/g, reaction time3.5h, the degree of hydrolysis was14.26%, the amidenitrogen content was3.07mmol/g protein, which was18.41g/100g glutamine.Then, by using ultrafiltration and macroporous absorbent resin, glutamine peptides weregraded and desalted. The glutamine content was richer in molecule weight1000-3000D andbelow1000D. After further static and dynamic adsorption of DA201-CⅡ were applied, the glutamine content of40%and60%elution fraction were improved from18.71g/100g to24.47g/100g and26.12g/100g respectively, together with the demineralization rate ran up to93.4%.Finally, the physico-chemical properties and antioxidant activity in vitro of fraction E60were investigated. The results indicated that fraction E60had good solubility, and the NSIwere above93%under different pHs. Meanwhile, its apparent viscosity was low, which wasslightly influenced by pH. And it had good thermal stability after high pressure sterilization,whose glutamine decomposition rate was only6.823%. As for its antioxidant activity in vitro,it showed the ability of DPPH scavenging, Fe2+chelating and reduction, which could be aneffective and potential natural antioxidant. |
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