Abstract: Free, conjugated, and bound phenolic acids in ten vegetables and vegetable products, including cow pea, broccoli, soybean sprouts, eggplant, potato, cucumber, spinach, Chinese cabbage, potato, and ketchup were identified and quantified by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results indicated that phenolic acid contents varied greatly among the vegetables. Of all the vegetables, Chinese cabbage contained the highest levels of free phenolic acids, while the highest amount of conjugated phenolics was determined in cow pea, followed by spinach, which showed the highest levels in bound phenolic acids. Principle component analysis (PCA) revealed some key compounds that could differentiate among these vegetables. p-Coumaric acid was identified as a characteristic component of cow pea. Ferulic acid and isoferulic acid were characteristics components that could differentiate spinach from the other kinds. In addition, sinapic acid was found to be a characteristic substance in cabbage. The results from this study can contribute to the development and application of functional components of vegetables.

Key words: phenolic acid, vegetables, characteristic components, UPLC-MS/MS, principal component analysis (PCA)