Concentrations of specific phenolic compounds in six red sorghums influence nutrient utilisation in broiler chickens

•Six red sorghum varieties from the 2009 Liverpool Plains harvest were characterised.•All six sorghums were ‘tannin-free’ as they lacked pigmented testas.•Concentrations of a range of phenolic compounds were determined.•The six sorghums had been evaluated in broiler bioassays.•Specific phenolic compounds negatively influenced energy utilisation in broilers.

Concentrations of polyphenolic compounds and free, conjugated and bound phenolic acids were determined in six red grain sorghum varieties harvested on the Liverpool Pains in 2009. Categories of polyphenolic compounds quantified included total phenolics, anthocyanins, flavan-4ols, luteolinidin, apigeninidin, 5-methoxy-luteolinidin, 7-methoxy-apigeninidin, apigenin, luteolin, eriodictyol and naringenin. Phenolic acids that were quantified included p-hydroxybenzoic, vanillic, caffeic, p-coumaric, ferulic, syringic and sinapic acids. These sorghums were also extensively characterised for additional properties including rapid visco-analysis (RVA) of starch pasting profiles, protein solubility and quantification of kafirin and phytate. A pigmented testa was not detected in the six varieties by the quantal Clorox bleach test, which indicated that they were Type I sorghums that do not possess condensed tannin. This was confirmed by vanillin assays. The six varieties were incorporated into unprocessed sorghum–casein mash diets and offered to broiler chickens to compare nutrient utilisation parameters and protein (N) digestibility coefficients. One objective of this study was to assess if non-tannin phenolic compounds influence energy utilisation in broiler chickens. Negative correlations between certain conjugated phenolic acids in sorghum and parameters of energy utilisation (AME, ME:GE ratios, AMEn) in birds were observed. For example, p-coumaric (r = −0.826), ferulic (r = −0.831) and total conjugated phenolic acids (r = −0.832) were negatively correlated with ME:GE ratios to significant (P < 0.05) extents. Interestingly, protein solubility was positively correlated to AME (r = 0.874), ME:GE ratio (r = 0.862) and AMEn (r = 0.837) to significant (P < 0.05) extents. This study suggests that specific phenolic compounds, namely conjugated phenolic acids of which ferulic and p-coumaric acids were the most abundant, negatively influence energy utilisation in sorghum-based broiler diets. Therefore, our tentative conclusion is that specific non-tannin phenolics are deleterious rather than innocuous components of grain sorghum in the context of chicken-meat production.