Fermentation in Human Subjects of Nonstarch Polysaccharides in Mixed Diets, but Not in a Barley Fiber Concentrate, Could Be Predicted by In Vitro Fermentation Using Human Fecal Inocula

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Abstract
The fermentation of nonstarch polysaccharides (NSP) contained in a low fiber diet, two high fiber diets high or low in protein, and a barley fiber concentrate was determined in balance experiments in six women and in an in vitro batch system using fecal inocula obtained from these same women. In vitro fermentations were performed with fiber residues prepared from duplicates of the fiber-containing foods consumed during the balance trials. Fermentation of total NSP in humans was 83.8 ± 0.9% (low fiber diet), 61.8 ± 3.6% (high fiber diet high in protein), 59.2 ± 3.9% (high fiber diet low in protein) and 31.2 ± 7.4% (barley fiber concentrate). Fermentation in vitro differed from fermentation in humans by −4.0 ± 1.6% (low fiber diet, P < 0.05,), 4.9 ± 3.7% (high fiber diet high in protein), 8.8 ± 3.0% (high fiber diet low in protein, P < 0.01) and 19.7 ± 8.0% (barley fiber concentrate, P < 0.05). Differences between in vivo and in vitro fermentation were most pronounced for NSP-glucose, i.e., cellulose. Production of short-chain fatty acids in vitro corresponded to the fermentability of NSP. The yield of short-chain fatty acids per gram of fermented NSP was similar for the diets (8.8–9.4 mmol) but lower for the barley fiber concentrate (7.4 mmol, P < 0.05). Although differences between the fermentation measured in humans and in vitro were significant for two diets, the magnitude of the differences was such that fermentation of NSP in mixed diets could be predicted with sufficient accuracy in vitro, whereas agreement between the fermentation in vivo and in vitro of NSP in the barley fiber concentrate was not satisfactory.