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High-Amylose Starch Reduces Colonic and Urinary p-Cresol Level in Rats Fed a High Tyrosine Diet Compared with an Inulin-based Diet

Bixiao CHEN1, Yue DING2, Tomoyuki NAKAGAWA1, 2, Takashi HAYAKAWA1, 2

1United Graduate School of Agricultural Science, Gifu University,
2Graduate School of Applied Biological Sciences, Gifu University

Two luminacoids, high-amylose starch (HAS) and inulin were compared to assess their ability to reduce cecal and urine phenolic compounds. For 3 weeks, Wistar rats were fed either the AIN-76 based modified diet (C-diet, negative control), a C-diet supplemented with 5% tyrosine (T-diet, positive control), a T-diet supplemented with 20% HAS (HAST-diet), a 3% inulin diet (I8T-diet, with an average degree of polymerization of 8), or a 3% inulin diet (I16T-diet, with an average degree of polymerization of 16). Urine was collected over 24 h on day 20 and ceca were collected under anesthesia on the last day. The concentration and amount of phenolic compounds (phenol and p-cresol) in ceca increased in rats fed the T-diet and p-cresol was the major compound. The HAST-diet decreased both the concentration and amount of p-cresol in ceca, but inulin did not. The amount of urinary p-cresol excretion decreased signifiantly in rats fed the HAST-diet compared with those fed the T-diet, but this was not the case with the inulin-based diets. Most of the urinary phenolic compounds were conjugated. The amount of n-butyrate in the ceca of rats fed the HAST-diet and I8T-diet was signifiantly higher compared with rats fed the T-diet. The amount of propionate in ceca and cecal pH were positively correlated with the total amount of p-cresol in the urine. As a consequence, both the HAST-diet and the I8T-diet increased the amount of n-butyrate in the cecum, however, only the HAST-diet reduced p-cresol in the cecum and urine.
Key words: high-amylose starch, inulin, n-butyrate, phenol, p-cresol

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