Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2007
Publication Date: 5/31/2007
Citation: Gu, L., House, S.E., Prior, R.L., Rooney, L. 2007. Sorghum bran in the diet dose dependently increased excretion of catechins and microbial derived phenolic acids in female rats. Journal of Agricultural and Food Chemistry. 55(13):5326-5334.
Interpretive Summary: Sorghum is said to be the fifth most important cereal crop in the world after wheat, rice, corn, and barley. Brown sorghum contains high level of polyphenols procyanidins, which are powerful antioxidant and thought to be beneficial for human health. But, it not clear if sorghum procyanidins can be well absorbed. We fed the sumac brown sorghum bran to female rats for 50 days and found two classes of metabolites in the blood and urine after sorghum feeding, suggesting that at least some procyanidins are absorbed. We also observed progressive and significant degradation of procyanidins in the cecum and colon. Future work will determine if this level of absorption provides any health advantage.
Technical Abstract: Sorghum bran is concentrated with procyanidins (predominately polymers), which may be beneficial for health in humans; however, the bioavailability of procyanidins is not well understood. Female Sprague-Dawley rats were fed an AIN93G diet containing 0, 5, 10, 20, or 40% Hi-tannin sorghum bran (n=5-7 for each group) for 50 days. Sorghum bran contained 23.3 mg/g of procyanidins. Urinary excretion of catechin, epicatechin, methylated catechins, and phenolic acids were analyzed using LC-MS/MS. Sorghum bran dose dependently increased urinary excretion of catechin (0 to 2.2 nmol/day) and 3'-O-methylcatechin (0 to 9.5 nmol/day). Their serum concentration also increased with dose (range of 0-14 nM for 3'-O-methylcatechin). Among the fourteen phenolic acids analyzed, 3,4-dihydroxybenzoic acid, 3-methoxyl-4-hydroxybenzoic acid, and 4-hydroxyphenylacetic acid dominated in the serum (1.8-8 µmol/L). In the urine, 3-methoxy-4-hydroxyphenylacetic acid, 3-hydroxyphenylacetic acid, and 3-hydroxyphenylpropionic acid dominated and their excretion increased significantly with level of sorghum bran in the diet. Summed phenolic acid excretion was 0.8 'mol/day in the control group and increased to 23 'mol/day for 40% sorghum bran group. Hippuric acid excretion ranged from 2.2 to 16.2 'mol/day and peaked in the 10% sorghum bran group. On the basis of chromic oxide, a non-absorbable marker, total procyanidins and polymers disappeared progressively, and significant degradation occurred in the cecum and colon. Procyanidins in sorghum are bioavailable as catechins; however, bacteria-derived phenolic acids were the predominant metabolites. Procyanidins degraded uniformly throughout the GI tract. Depolymerization was not observed.