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Rat Cecal Inocula Produce Different Patterns of Short-Chain Fatty Acids than Fecal Inocula in In VitroFermentations^1,2,3,

Department of Nutritional Sciences, University of Wisconsin-Madison, Madison, WI 53706

The effects of bacterial collection site, bacterial adaption to substrate and duration of fermentation on short-chain fatty acid (SCFA) production were studied using an in vitro fermentation system. Cecal and fecal inocula from rats fed purified diets containing 100 g/kg dietary fiber from canned peas or psyllium seed husk, or a nonpurified diet containing 170 g/kg dietary fiber fermented ileal excreta from colectomized rats fed a purified diet containing 100 g/kg dietary fiber from canned peas. The SCFA concentration, measured by gas chromatography, in anaerobic fermentations of 0, 3, 6, 12, 24, 48, 72 and 96 h, increased (P < 0.05) through 72 h. Compared with fecal inocula, cecal inocula produced SCFA at greater (P < 0.05) initial rates, more (P < 0.05) total SCFA and a greater (P < 0.05) proportion as n-butyrate. Inocula from rats fed the pea or nonpurified diets produced SCFA at greater (P < 0.05) molar proportions as acetate and less (P < 0.05) as propionate than inocula from rats fed psyllium seed husk at most time points. We conclude that collection site, adaptation of bacteria to the substrate to be fermented and duration of fermentation significantly influence the results of in vitro fermentation studies.

KEY WORDS: • dietary fiber • in vitro fermentation • short-chain fatty acids • gas chromatography • rats

¹ Presented in part at Experimental Biology 94, April 24–28, 1994, Anaheim, CA [Monsma, D. J. & Marlett, J. A. (1994) In vitro fermentation of rat ileal excreta is affected by source of bacterial inoculum. FASEB J. 8: A152 (abs.)].

² Supported by National Institutes of Health grant DK21712 and by the College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, WI.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

Manuscript received 11 November 1994. Revision accepted 17 May 1995.