Characterization of non-volatile compounds in tom yum soup using high performance liquid chromatography-tandem mass spectrometry

Abstract

In this work, high performance liquid chromatography hyphenated with tandem mass spectrometry (HPLC-MS/MS) was developed and validated for simultaneous determination of 31 targeted non-volatile compounds, such as 2 organic acids, 20 amino acids and 9 phenolic acids, in Tom Yum ingredient, Tom Yum soup made from the fresh ingredients and commercial Tom Yum pastes, where the main Tom Yum ingredients include galangal, lemongrass, kaffir lime leaves, Bird’s eye chili, lime juice and fish sauce. The following HPLC-MS/MS conditions were used: a PoroShell C18 column (4.6 x 100 mm, 2.7 µm) using a gradient elution of A:B mobile phase at a flow-rate of 0.3 mL/min, where A consisted of 0.1%v/v formic acid in water and B consisted of 0.1%v/v formic acid in methanol. This developed HPLC-MS/MS method can determine these targeted non-volatile compounds with the limit of detection and the limit of quantitation in the range of 0.010 – 0.62 and 0.032 – 1.9 mg/L, respectively. Using pooled diluted Tom Yum soup spiked with standard at known concentrations, acceptable accuracy for quantitative analysis was obtained with the recoveries in a range of 62-115%, which is 98.6% of the recovery data being within 80-110% for the analytes concentration in the range of 0.06-3 ppm. An accepted level of precision intraday and interday were also obtained in the range of 9-16 with RSD.

From the HPLC-MS/MS analysis of ingredient and Tom Yum soup, the main sources of targeted non-volatile compounds were obtained: two organic acids including citric acids of 2714 mg/kg and malic acid of 212 mg/kg from lime juice, fourteen amino acids from fish sauce, another six amino acids from lime juice, phenolic compounds from various sources. The top five amino compounds found in Tom Yum soup were aspartic acid, phenylalanine, isoleucine, valine and leucine in the range 370-623 mg/kg. In addition, acetoxy chavicol acetate of 98 mg/kg, mainly from galangal, was found to be the predominant phenolic compounds found in Tom Yum soup. Note that the unit of mg/kg here refers to the mass of a hot water-dissolving compounds in prepared Tom Yum paste. This developed HPLC-MS/MS analysis can be used for quantitative determination and identify the sources of non-volatile compounds in Tom Yum soup.