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

Abstract

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 monogalloyl to hexagalloyl hexosides. Interestingly, tetragalloyl, pentagalloyl, and hexagalloyl hexosides were identified as the possible 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.

Ellagic Acid: A Review on Its Natural Sources, Chemical Stability, and Therapeutic Potential

“…The HHDP moiety arises due to the oxidative C-C bond formation between neighboring galloyl residues within the ellagitannin structure. Another group of hydrolyzable tannins is represented by gallotannins (polygalloyl esters of glucose or other polyol carbohydrate), which have a simpler structure and more restricted distribution in nature than ellagitannins [160,161]. A molecular precursor of both gallotannins and ellagitannins in plants is gallic acid (3,4,5-trihydroxybenzoic acid), and the initial stages of biosynthesis are common to both of these groups of phytochemicals [158].…”

Neglected and Underutilized Legume Crops: Improvement and Future Prospects

“…Reports indicated that sword bean originated from the Asian continent and is now known in the tropics as an introduced species. The red sword bean is one of the edible beans of China reportedly rich in antioxidant polyphenols with great medicinal uses [41,42]. Furthermore, the seed coat of the bean is rich in gallic acid and its derivatives, mainly gallotannins, a common trait found in legume polyphenols [41].…”

“…The red sword bean is one of the edible beans of China reportedly rich in antioxidant polyphenols with great medicinal uses [41,42]. Furthermore, the seed coat of the bean is rich in gallic acid and its derivatives, mainly gallotannins, a common trait found in legume polyphenols [41]. The chemical composition of seeds of sword bean has been reported and compares quite well with soybean [43][44][45].…”

Bioactive Compounds of Jack Beans (Canavalia Species)

“…Tannins in ripened seeds and ripened split beans of C. cathartica and C. maritima decreased substantially on cooking [24,44]. Gallotannins have been extracted from red bean coat of C. gladiata which showed potent antioxidant as well as antibacterial activity [46].…”