In vitro fermentation of various food fiber fractions

Dietary fiber fractions (DFF) were fermented in vitro with human fecal inocula to study fiber fermentability and production of short-chain fatty acids (SCFA). Amylolytic and proteolytic enzyme treatment using the Association of Official Analytical Chemists enzymatic-gravimetric procedure reduced processed food fiber products to DFF by removing gastric enzyme-digestible (nonresistant) components. Total 24-h SCFA production from DFF decreased in the following order: fig > oat = soy > pea > apple > corn = wheat > pear. SCFA production was proportional to the fermentability of these fibers. Fermentation of DFF from fruits such as pear, apple, and fig produced low amounts of butyrate. In contrast, less acetate and more propionate and butyrate were produced by fermentation of oat and soy DFF. Major fiber constituents, resistant starch (RS), beta-glucan, and pectin were also fermented. RS, isolated from starch, produced acetate more slowly than the starch. beta-Glucan produced propionate and butyrate in higher amounts than did pectin, starch, and RS. This study demonstrates that the fermentability of DFF and the production of SOFA differ among food products. In vitro fermentation of DFF is useful in estimating SCFA production in the human colon.