Release of Covalently Bound Ferulic Acid from Fiber in the Human Colon

The action of wheat bran as a potential colon anticarcinogen is related partly to its low fermentability in the large intestine. Phenolic acids are highly bioactive components and also limit degradability of wheat bran in ruminants. Therefore, the solubilization of covalently bound phenolic acids during the fermentation of wheat bran in a human model colon was examined. Phenolics were only partially and relatively slowly solubilized from wheat bran, but were rapidly and fully solubilized from sugarbeet fiber; the levels of free ferulic acid in fermentation liquors remained very low and did not reflect the amounts solubilized from fiber sources. Xylanase and ferulic acid esterase activities were shown to be present. The released ferulic acid did not appear to bind noncovalently to the residual wheat bran fiber. Thus, fermentation in the gut alters the partition of esterified phenolic acids from the insoluble residue and the soluble fraction, where microbial ferulic acid esterase(s) can potentially yield free ferulic acid. Keywords: Ferulic acid; phenolic acids; plant cell walls; fiber; wheat bran; sugarbeet pulp; colon fermentation; phenolic antioxidants; esterases; xylanase