A Quantitative Determination of Amino Acids in the Tea Leaves (Part 2)

Abstract

A simple determination of total amino acids in tea leaves was investigated by ninhydrin method.The method was as follows : Sample solution prepared from 1g. of dried tea leaves by extraction with hot water is treated with the routine method of basic lead acetate. This solution is made to 100 ml. with water, after removed Pb with H2S. Take 0.25 ml. of sample solution, add 0.12ml. of pH 8 phosphate buffer solution and 0.1 ml. of ninhydrin solution to a test tube. Heat the mixed solution in a boiling water bath continuously 10 minutes. Make to 10 ml. with water, cool, and measure the absorbancy of the coloured solution at 570mμ with a spectrophotometer. Amount of total amino acids was calculated from the measured absorbancy by the calibration curve of theanine.The coefficents of variation of this method were 4.70-4.90%. A high correlation (r=0.980) was observed between the total amino acids content of this method and the sum of each amino acid content by an automatic amino acids analyzer.