Isolation and structure elucidation of the major individual polyphenols in carob fibre.
Although it is already known that carob fibre contains several classes of polyphenolic substances, a comprehensive analysis of these has not been conducted to date. Therefore, the major polyphenolic compounds were extracted with organic solvents, and, following fractionation by normal-phase column chromatography on silicic acid, their structures were elucidated by liquid-chromatography electrospray-ionisation mass spectrometry (LC-ESI), nano-electrospray-ionisation mass spectrometry (ESI-MS), and gas-chromatography mass spectrometry (GC-MS). In addition, complete 1H and 13C NMR assignments were obtained for the isolated gallotannins 1,6-di-, 1,2,6-tri- and 1,2,3,6-tetra-O-galloyl-beta-D-glucose. Carob fibre was found to contain a rich variety of phenolic antioxidants. A total of 24 polyphenol compounds were identified with a yield of 3.94 g/kg (dry weight). The profile was dominated by gallic acid in various forms: free gallic acid (42% of polyphenols by weight), gallotannins (29%), and methyl gallate (1%), while simple phenols, mainly cinnamic acid, made up about 2% of the total. Flavonoids represented 26% of the polyphenols, and the major components were identified as the glycosides myricetin- and quercetin-3-O-alpha-L-rhamnoside (ca. 9% and 10%, respectively). These data indicate that carob fibre is rich in both amount and variety of phenolic antioxidant substances, and its inclusion in the diet may have chemopreventive properties.
Owen
R W
RW
Division of Toxicology and Cancer Risk Factors, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany. r.owen@dkfz-heidelberg.de
Haubner
R
R
Hull
W E
WE
Erben
G
G
Spiegelhalder
B
B
Bartsch
H
H
Haber
B
B
D002852:Chromatography, Ion Exchange; D004043:Dietary Fiber / Q000032:analysis*; D005419:Flavonoids / Q000737:chemistry* / Q000302:isolation & purification; D005685:Galactans; D008401:Gas Chromatography-Mass Spectrometry; D006868:Hydrolysis; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008351:Mannans; D010636:Phenols / Q000032:analysis / Q000737:chemistry* / Q000302:isolation & purification; D053149:Plant Gums; D059808:Polyphenols; D011134:Polysaccharides / Q000737:chemistry*; D012824:Silicic Acid / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization
D004043:Dietary Fiber; D005419:Flavonoids; D005685:Galactans; D007202:Indicators and Reagents; D008351:Mannans; D010636:Phenols; D053149:Plant Gums; D059808:Polyphenols; D011134:Polysaccharides; D012824:Silicic Acid; C017471:locust bean gum