Characterization of dietary fiber lignins from fruits and vegetables using the DFRC method.
Insoluble fiber fractions from 11 fruits and vegetables were investigated for their lignin composition using the derivatization followed by reductive cleavage (DFRC) methodology. To enrich lignin contents and to minimize polysaccharide excess that led to nonanalyzable DFRC chromatograms, the insoluble fibers were degraded by a carbohydrolases mixture. The residues that were found to be representative for the insoluble fiber lignins were analyzed. The investigated fibers differ considerably in their lignin contents and also in their lignin compositions. With the exception of radish fiber, only trace amounts (or none) of the products resulting from p-hydroxyphenyl units were detected. Lignins noticeably differed in the ratio of the DFRC products resulting from syringyl units (S) and guaiacyl (G) units (G/S ratios ranged from approximately 39 to 0.2). The insoluble fiber lignins were classified as G-rich lignins (G/S ratio > 3; carrot, spinach, kiwi, curly kale, radish, and asparagus), S-rich lignins (S/G ratio > 3; rhubarb), or balanced lignins (0.3 < G/S ratio < 3; pear, apple, small radish, and kohlrabi). Information about further structural characteristics, for example, cinnamyl endgroups, was obtained from the analysis of DFRC minor products.
Bunzel
Mirko
M
Institute of Biochemistry and Food Chemistry, Department of Food Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany. mirko.bunzel@uni-hamburg.de
Seiler
Annika
A
Steinhart
Hans
H
D000085:Acetates; D004043:Dietary Fiber / Q000032:analysis*; D005504:Food Analysis / Q000379:methods*; D005638:Fruit / Q000737:chemistry*; D006867:Hydrolases / Q000378:metabolism; D008031:Lignin / Q000032:analysis*; D011134:Polysaccharides / Q000378:metabolism; D012995:Solubility; D014675:Vegetables / Q000737:chemistry*
D000085:Acetates; D004043:Dietary Fiber; D011134:Polysaccharides; D008031:Lignin; D006867:Hydrolases; C412887:acetyl bromide