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Front. Chem. | doi: 10.3389/fchem.2018.00039

Separation, Identification, and Bioactivities of the Main Gallotannins of Red Sword Bean (Canavalia gladiata) Coats

 Ren-You Gan1,  Kin Weng Kong2, Hua-Bin Li3, Kao Wu4, Ying-Ying Ge1,  Chak Lun Chan5 and  Harold Corke1*
  • 1Department of Food Science and Engineering, School of Agriculture and Biology, Shanghai Jiao Tong University, China
  • 2Department of Molecular Medicine, Faculty of Medicine, University of Malaya, Malaysia
  • 3Guangdong Provincial Key Laboratory of Food, Nutrition and Health, School of Public Health,, Sun Yat-sen University, China
  • 4Glyn O. Philips Hydrocolloid Research Centre, Hubei University of Technology, China
  • 5School of Biological Sciences, University of Hong Kong, Hong Kong

The red sword bean (Canavalia gladiata) is an underutilized edible bean cultivated in China. It was previously found to have the highest content of antioxidant polyphenols among 42 edible beans, mainly gallic acid and gallotannins in its red bean coat, an apparently unique characteristic among edible beans. In this study, the main phenolic compounds in red sword bean coats were further separated by Sephadex LH-20 column chromatography, and identified by LC-MS/MS. Furthermore, the FRAP and ABTS antioxidant activities and antibacterial activity (diameter of inhibition zone, DIZ) of main gallotannin-rich fractions were tested. Our results showed that gallotannins of red sword bean coats were mainly comprised of nonogalloyl to hexagalloyl hexosides. Interestingly, tetragalloyl, pentagalloyl, and hexagalloyl hexosides were identified as the main candidates responsible for the red color of the coats. On the other hand, gallotannin-rich fractions exhibited diverse antioxidant and antibacterial activities, and tetragalloyl hexoside overall had the highest free radical scavenging and antibacterial activities. The degree of galloylation did not completely explain the structure-function relationship of gallotannins isolated from red sword bean coats, as there should exist other factors affecting their bioactivities. In conclusion, red sword bean coats are excellent natural sources of gallotannins, and their gallotannin-rich extracts can be utilized as natural antioxidant and antibacterial agents with potential health benefits as well as application in food industry.

Keywords: Canavalia gladiata, Gallotannins, antioxidant activity, Antibacterial activity, SEPARATION

Received: 28 Dec 2017; Accepted: 14 Feb 2018.

Edited by:

Marcello Iriti, Università degli Studi di Milano, Italy

Reviewed by:

Javad Sharifi-Rad, Shahid Beheshti University of Medical Sciences, Iran
Michael Gänzle, University of Alberta, Canada  

Copyright: © 2018 Gan, Kong, Li, Wu, Ge, Chan and Corke. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Harold Corke, School of Agriculture and Biology, Shanghai Jiao Tong University, Department of Food Science and Engineering, Agriculture and Biology Building, Shanghai Jiao Tong University, No. 800, Dongchuan Road,, Minhang, Shanghai, China, Shanghai, 200240, Shanghai, China, hcorke@yahoo.com