Analysis of polyphenols in brewer's spent grain and its comparison with corn silage and cereal brans commonly used for animal nutrition

•Aqueous-alkaline extraction showed the highest recovery of polyphenol monomers.•Microwave was the best extraction procedure for brans.•Maceration was better than microwave for corn silage brewer's spent grain.•The highest antioxidant activity was found when aqueous alkaline condition is used.•Brewer's spent grain has higher content of polyphenols than silage and brans.

Brewer's spent grain (BSG) could be tested as an alternative source of polyphenols in animal nutrition. Proper extraction and analytical methods are critical for quantification. Thus, extraction for BSG, corn silage, and brans of rice, corn, and wheat were studied for the highest yield of polyphenols. A method for 18 phenolic monomers by HPLC-DAD was developed, validated, and applied to samples. An aqueous solution of NaOH (0.75% w/v) using integral samples for extraction resulted in the highest values for colorimetric measurements in all analyzed sources. Method by maceration showed the highest phenolic yield when applied in corn silage and BSG. However, for brans the best method was microwave assisted. Results from HPLC-DAD analysis clearly showed that native structures of phenolic compounds were simplified to its monomers allowing quantification and sample discrimination. BSG had the highest concentration of polyphenols and could be a promising and innovative source for animal feed studies.