PubMed · 16857852
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Francisco Guarner. 2006. Prebiotics and mucosal barrier function.. https://doi.org/10.1093/jn%2F136.8.2269
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Compositional information for lignins in food is rare and concentrated on cereal grains and brans. As lignins are suspected to have important health roles in the dietary fiber complex, the confusing current information derived from nonspecific lignin determination methods needs to be augmented by diagnostic structural studies. For this study, lignin fractions were isolated from kiwi, pear, rhubarb, and, for comparison, wheat bran insoluble dietary fiber. Clean pear and kiwi lignin isolates allowed for substantive structural profiling, but it is suggested that the significance of lignin in wheat has been overestimated by reliance on nonspecific analytical methods. Volume integration of NMR contours in two-dimensional (13)C-(1)H correlation spectra shows that pear and wheat lignins have comparable guaiacyl and syringyl contributions and that kiwi lignins are particularly guaiacyl-rich (approximately 94% guaiacyl) and suggest that rhubarb lignins, which could not be isolated from contaminating materials, are as syringyl-rich (approximately 96% syringyl) as lignins from any known natural or transgenic fiber source. Typical lignin structures, including those newly NMR-validated (glycerols, spirodienones, and dibenzodioxocins), and resinols implicated as possible mammalian lignan precursors in the gut are demonstrated via their NMR correlation spectra in the fruit and vegetable samples. A novel putative benzodioxane structure appears to be associated with the kiwi lignin. It is concluded that the fruits and vegetables examined contain authentic lignins and that the detailed structural analysis exposes limitations of currently accepted analytical methods.
Paenibacillus sp. strain HC1 is the first bacterium capable of growing on rice bran hemicellulose as a sole carbon source. Two xylanases (Xyl-I and -II) were purified from the bacterial culture fluid and enzymatically characterized. Xyl-I and -II showed monomer forms with molecular masses of 30 and 18kDa, respectively, and were most active at around pH 5.0 and 45 degrees C. Xylooligosaccharides were degraded to xylobiose and xylose by Xyl-I, but not by Xyl-II, suggesting that Xyl-I plays an important role in complete depolymerization of xylan. Both enzymes acted endolytically on rice bran hemicellulose, indicating that Xyl-I and -II contribute to the structure determination and practical use of the polysaccharide, an unutilized biomass in technology.
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