Identification of soluble free, soluble conjugated and insoluble bound phenolics in tomato seeds and their radical scavenging and antiproliferative activities

Authors: LI(POSTDOC), YANFANG - University Of Maryland; LIU (POSTDOC), ZHIHAO - University Of Maryland; TAMIA, GILLIAN MANKA - University Of Maryland; He, Xiaohua; Sun, Jianghao; Chen, Pei; LEE, SEONG-HO - University Of Maryland; Wang, Thomas - Tom; GAO, BOYAN - Shanghai Jiaotong University; XIE, ZHUOHONG - United States Pharmacopeia; YU, LIANGLI - University Of Maryland

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2022
Publication Date: 7/12/2022
Citation: Li, Y., Liu, Z., Tamia, G., He, X., Sun, J., Chen, P., Lee, S., Wang, T.T., Gao, B., Xie, Z., Yu, L. 2022. Identification of soluble free, soluble conjugated and insoluble bound phenolics in tomato seeds and their radical scavenging and antiproliferative activities. Journal of Agricultural and Food Chemistry. 70(29):9039-9047. https://pubs.acs.org/doi/10.1021/acs.jafc.2c03418.
DOI: https://doi.org/10.1021/acs.jafc.2c03418

Interpretive Summary: Tomato seeds are by-products of tomato processing, and they are rich in phenolic compounds. The aim of this study was to identify phenolic compounds in the soluble free, soluble conjugated and insoluble bound fractions of tomato seeds and to evaluate their potential health benefits. In addition to known ones, five new compounds including indole-3-acetyl-L-aspartic acid, coumaroyl tyramine, N-feruloyltyramine, hydroxytyrosol and methoxycinnamaldehyde were identified for the first time. The insoluble bound phenolic fraction was found to have a greater total phenolic content value, stronger free radical scavenging activities, and stronger inhibitory effect against HCT-116 human colorectal cancer cells compared with the soluble free and soluble conjugated fractions. The insoluble bound and soluble free fractions also exhibited strong inhibition on the proliferation of HCT-116 cells. These results provide useful information for future utilization of tomato seeds as value-added ingredients in functional foods.

Technical Abstract: The soluble free, soluble conjugated, and insoluble bound phenolic compounds in tomato seeds were extracted and analyzed using ultra-high-performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS). Total phenolic content (TPC), free radical scavenging activities, along with the anti-proliferation effects against human colorectal cancer cell line (HCT-116) were also examined for the soluble free, soluble conjugated and insoluble bound phenolic fractions. Thirteen, seven and ten compounds were tentatively identified in the soluble free, soluble conjugated, and insoluble bound phenolic fractions, including indole-3-acetic acid derivatives, flavonoids and feruloyl tyramines. The insoluble bound phenolic fraction was observed to have a greater TPC value and stronger free radical scavenging activities against ABTS•+, DPPH• and peroxyl radical, as well as a stronger inhibitory effect against HCT-116 cells compared with the soluble free and the soluble conjugated fractions. Soluble free and insoluble bound fractions significantly inhibited the proliferation of HCT-116 cell line and no anti-proliferation effects were observed with the soluble conjugated fraction under the experimental conditions. The results may provide a foundation for future application of tomato seeds as nutraceuticals in dietary supplements and functional foods.