Identification of 4-O-p-coumaroylquinic acid as astringent compound of Keemun black tea by efficient integrated approaches of mass spectrometry, turbidity analysis and sensory evaluation

Hydroxycinnamoyl quinic acids are important phenolic acids in tea, particularly fermented teas. However, there have been fewer studies that have confirmed their taste properties. The aim of this study was to investigate the astringent compounds in Keemun congou black tea (KBT) using a combination of mass spectrometry, turbidity analysis, and sensory evaluation. Turbidity analysis determined that p-coumaroylquinic acids were the astringent contributing compounds in KBT. Moreover, the separated compound D16 was identified as trans-4-O-p-coumaroylquinic acid (trans-4-O-pCoQA) by nuclear magnetic resonance spectroscopy and first confirmed to be the astringent contributing compound in KBT by sensory evaluation. Its astringent threshold concentration was tested to be 38 mu M. The trans-4-O-pCoQA content in eight KBT samples of various grades ranged from 40.20 +/- 0.15 similar to 65.53 +/- 0.22 mu M. Turbidity analysis combined with sensory evaluation could be a powerful tool for identifying critical compounds responsible for the astringent taste.

Automated summary

This study identified p-coumaroylquinic acids as the astringent contributing compounds in Keemun congou black tea, with trans-4-O-p-coumaroylquinic acid (trans-4-O-pCoQA) confirmed as the main astringent compound. Turbidity analysis coupled with sensory evaluation proved to be an effective tool for identifying critical compounds responsible for the astringent taste in the tea.