Simultaneous Determination of Organic Acids of Ancient and Commercial Pu-Erh Tea Using Reversed-Phase HPLC-DAD

Tee, Chi Ren (2025) Simultaneous Determination of Organic Acids of Ancient and Commercial Pu-Erh Tea Using Reversed-Phase HPLC-DAD. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Pu-erh tea is a Chinese black tea which has various health benefits, such as anti-aging, antioxidant, and slimming effects. While ancient pu-erh tea originates from pu-erh tea trees that aged from hundred to thousand years, commercial pu-erh tea comes from plantations. Pu-erh tea contains various organic acids which are oxalic acid, tartaric acid, ascorbic acid, malonic acid, lactic acid, acetic acid, citric acid, maleic acid, succinic acid, malic acid, and propionic acid, which were determined and quantified in this project by reversed phase HPLC-DAD. 20mM KH2PO4 (pH 2.50) and methanol were used to separate the organic acids in the C18 column by gradient elution. The method was optimised by altering different parameters such as mobile phase, column temperature, detection wavelength, and injection volume. Low and high buffer concentration, higher pH value, and higher column temperature resulted in overlapping of peaks. Five standards from 10.42 mg/L to 216.81 mg/L were prepared to assess the linearity, repeatability, and intermediate precision. R2 values were obtained at the range of 0.9939 - 0.9989, and the RSD values were less than 4.0. LOD and LOQ values were from 0.08 mg/L to 0.69 mg/L, and 0.24 mg/L to 2.10 mg/L respectively. 0.5g of sample was grinded, and its organic acids were extracted in 40mL boiling water for 20 minutes. The sample solution was filtered and analysed. The percent recovery obtained was from 80.25 % to 144.92 %, whereas the matrix effect was from -37.52 % to 31.74%. In conclusion, ancient pu-erh tea had more organic acid than commercial pu-erh tea, which was greatly contributed by the presence of propionic acid.