Study On The Fixation Technology Of Mulberry Leaf Tea And Its Antioxidant Effects In Vitro

The target of this paper is to develop a new type of convenience edible tea beverages which used mulberry leaf as materials. We adopt the green tea processing technology as the preparation method of mulberry tea, especially considering using different kinds of fixation methods which has the greatest impact on the quality of tea. The main research content includes the optimization of processing parameters of mulberry leaf tea, studying on the antioxidant activity of different solvent extracts in vitro and cellular antioxidant activity of mulberry leaf tea. We also take a comparison between them. The correlational analyses between the results of the two antioxidant activity evaluating methods were conducted. The results are as follows:1Study on fixation methods of mulberry leaf tea1.1Optimization of the fixation methods of mulberry leaf teaUsing single factor experiment and orthigonal test to determine the fixing temperature(microwave power), fixing time, the weight of leaves on microwave fixing, blanching fixing and steam fixing. Sensory evaluation and POD enzyme inactivation as the indicators of the effect of fixing, identify the best fixing technology as follow:The optimal conditions of microwave fixing:microwave power300W, microwave processing time2.5min, the weight of leaves90g.The optimal conditions of blanching fixing:blanching temperature95℃, blanching time4min, the weight of leaves120g.The optimal conditions of steam fixing:fixing time3.5min, the weight of leaves90g.Using these conditions above handled, fixing leaves acquired a high score of sensory evaluation:the grass leaf gas disappeared; the aroma composition spills the surface; the leaves feel soft, and its stems hard to break. Furthermore, POD enzyme which in the leaves were inactivated.1.2Effects of different fixation methods on the chemical components of mulberry leafFurther experiments is found out the optimum fixing way from the three methods. Using the quality of ingredients of taste and color and functional components as the main indexs, combined with sensory evaluation. The combined effect of display that microwave fixing is the best method. After microwave fixing, fixing leaves content of water extract12.36%; on the dry matter, taste and color quality of the major components of free amino acids was2.78%, soluble sugar3.48%; main functions polyphenol and flavonoid glycosides constituents8.72mg/g and5.53mg/g separately.2Study on the invitro antioxitant activity of mulberry leaf tea prepared by different fixation methods2.1Comparison and analysis on the invitro antioxidant activity of mulberry tea prepared with different fixation methodsAt the aspect of absorption ability of oxy-radical, the ORAC value of ethanol extracts of mulberry leaf tea prepared with three fixation methods were all higher than that of water extracts. And among which, the50%ethanol extract of mulberry leaf tea made with microwave fixation method had the strongest oxy-radical removing ability, with ORAC value of1437.4±96.25μmol/g; the ORAC value of water extract of mulberry tea made with blanching fixation method was the lowest, which was764.9±102.88μmol/g.In the comparison of DPPH free radical removing ability, the water extracts of mulberry leaf tea prepared with the three fixation methods all exhibited relatively strong free radical removing ability, and their removing effectiveness was all higher than50%and95%ethanol extracts. The75%ethanol solution extract of mulberry leaf tea made with microwave fixation method had the lowest IC50value, which was139.14±11.70μg/mL; which showed its DPPH clearing ability was the strongest.In the coparison of reducing power, the50%ethanol solution extract of mulberry leaf tea made with microwaving fixation method had the strongest reducing power. The50%ethanol solution extracts of mulberry leaf tea made with three fixation methods all exhibited relatively strong reducing power.2.2Correlation analysis of the total phenol and total flavonoids content and the antioxidant activity of mulberry leaf teaThe different dissolvents all had notable impact to the total phenol content of mulberry tea extract, and the total phenol content in water extracts of three types of mulberry leaf tea was all relatively higher. The total flavonoids in the water extracts of mulberry leaf tea increased first along with the increase of ethanol concentration, and then decreased; when ethanol concentration was75%, the total flavonoids content all reached maximum value; and to compare with other solvent extracts, there were all significant differences(p<0.05).Although the water extract of mulberry leaf tea had the strongest antioxidation capacity, neither of its total phenol nor total flavonoids could not be used to accurately evluate the antioxidant ablility of different extracts of mulerry tea.3Research on the intracellular antioxidant activity of mulberry leaf tea3.1Comparative analysis on the intracellular antioxidant capacity(CAA-RBC) of different mulberry leaf tea extractsResults of CAA-RBC method showed that the situation of cellular antioxidant activity of diffetent solvent extracts of mulberry leaf tea was:50%ethanol>75%ethanol>95%ethanol>water. The intracellular anti oxidant acitivity was the lowest, with EC50value of380.813μg/mL, which was about one fourth of that of50%ethanol extract; to compare with EC50values of ethanol extracts of differemt concentrations, there were always outstanding differentces(P<0.05).The antioxidant activity of50%ethanol extracts of mulberry leaf tea was a little bit higher than that of75%ethanol extract.3.2Correlation analysis of the functional component content and intracellular antioxidant activity of mulberry leaf teaThe intracellular antioxidant activity had relatively weaker positive correlation with the content of total phenol and total flavonoids, and the correlation coefficients were0.216and0.129respectively. This was similar to the results got through vitro antioxidation method. There was no direct correlation between cellular oxidation resistance and chemical oxidation resistance of different extracts of mulberry leaf tea. Components with very strong chemical oxidation resistance all had very small cellular antioxitant activity, and their EC50could not be calculated. Therefore, materials with very strong chemical oxidation resistance may not be able to enter a body and clear out free radicals. That is to say it is not scientific to evaluate oxidation resistance of a material solely with the chemical antioxidation method. It is recommended to evaluate antioxidant activity comprehensively through building a cell model.