Effect of Diets Containing Sorghum Fractions on Antioxidant Capacity of Dogs and Phenolic Acids of Both Food and Plasma Measured By High Performance Liquid Chromatography (HPLC)

Sorghum pericarp is abundant in antioxidant phenolics that might benefit companion animal diets. Key among these are ferulic (FA) and p-coumaric (PCA) acids. The objective of this study was to determine the effects of diets containing sorghum fractions rich in phenolic acids on antioxidant activity in dog plasma. Four nutritionally similar diets were extruded containing whole sorghum (WSD), sorghum flour (FLD), sorghum mill-feed (MFD), or a combination of corn, wheat and rice (ratio 1:1:1; CON), and fed to twelve Beagle dogs in a replicated 4 x 4 Latin square design experiment. At the end of each period blood was collected, plasma separated, and stored (-80C) until analyses. The experiment was approved by the KSU Institutional Animal Care and Use Committee. Antioxidant activities in dog plasma were measured using an Oxygen Radical Absorbance Capacity (ORAC) kit (Cell Biolabs, Inc., San Diego, CA) and phenolic acids (following extraction) by HPLC using a Spherisorb S5 ODS2 C18 reversed-phase column. Means of plasma phenolics and ORAC were separated using multivariate analysis of variance (MANOVA) with the GLM procedure of the statistical analysis software (SAS, v 9.4). Dietary phenolic acid means were separated with analysis of variance using the GLM procedure (SAS, v 9.4). Unexpectedly, whole corn had the greatest (P<0.05) PCA and FA (410 and 2711 ppm, respectively), followed by sorghum mill-feed (372 and 1311 ppm, respectively). Rice and sorghum flour had the lowest (P<0.05) FA (average 236 ppm, respectively), and rice, sorghum and wheat flour had the lowest PCA (average 30.8 ppm). Wheat flour and whole sorghum had similar and intermediate FA concentration (average 525 ppm). P-coumaric concentration was not different among CON, WSD, or FLD (average 128 ppm), but was higher (P<0.05) for MFD (298 ppm). Ferulic acid was lowest (P<0.05) in WSD and FLD (average 649 ppm), intermediate in CON (1028 ppm), and highest in MFD (1380 ppm). However, plasma FA and PCA did not differ across treatments (averages 0.143 and 0.095 ppm, respectively). Yet the ORAC of MFD was more than 2-fold (P<0.05) the value of the other treatments (20,482 vs average 8,923 μM TE/L). The study suggests that the FA and PCA concentrations in plasma or the diet was not related to the antioxidant capacity of dogs fed the dietary treatments .