Determination of tea polyphenols, caffeine and L-theanine in commercially available tea drinks

Tea polyphenols(TP),free amino acids,epigallocatechi gallate(EGCG),caffeine(CAF)and L-theanine(TA)in commercially available tea drinks were determined. The results indicated that the drinks’quality had no correlation with brands. The concentrations of TP,EGCG and CAF were highest in oolong tea drinks. All the oolong and jasmine tea drinks complied with the national standard in terms of TP concentration,but 15% green tea drinks and even 50% black tea drinks didn’t. Except 2 green tea drink samples,all conformed to the national standard in terms of CAF concentration.