A “berry” small inclusion: 40 types of commercial dog and cat kibble with added blueberries provide low levels of quercetin, free phenolics, and alkali-labile phenolics

Blueberries provide dietary polyphenols and are often included in dog and cat kibble as a source of antioxidants. For this study, we investigated the polyphenol content in commercial dog and cat extruded food that lists blueberries on their ingredient deck. We sampled 40 bags of kibble (18 cat and 22 dog) from four pet food stores in Guelph, Canada. High-performance liquid chromatography was employed for the determination of quercetin, free phenolics (caffeic acid; cinnamic acid; ferulic acid; gallic acid; hesperetin; naringin; p-coumaric acid; p-hydroxybenzaldehyde; protocatechuic acid; syringaldehyde; syringic acid; vanillic acid; vanillin), and antioxidant-protected alkali-labile phenolics (caffeic acid; chlorohenic acid; cinnamic acid; ferulic acid; gallic acid; hesperetin; naringin; p-coumaric acid; p-hydroxybenzaldehyde; protocatechuic acid; sinapic acid; syringaldehyde; syringic acid; vanillic acid; vanillin). Mean concentration ± SE was calculated for all assessed polyphenol types. The ANOVA procedure was used to determine if the intended species (cat or dog) affected quercetin and antioxidant-protected alkali-labile polyphenol concentrations. Quercetin concentrations were found at 5.05 ± 4.32 µg/g across all bags. Cat kibble had lower average concentrations of quercetin and alkali-labile phenolics compared to dog kibble, which is likely linked to the quantity of added fruits and vegetables. Concentrations of free phenolics were minimal to nonexistent for all kibble types. Dog and cat kibble containing blueberries do not provide significant amounts of dietary polyphenols and, therefore, do not contribute to enhanced sources of antioxidants and anti-inflammation. Future research should assess optimal polyphenol doses in healthy cats and dogs to determine the target doses to achieve physiological benefits.