HPLC Analysis Finds Low Polyphenol Content in Blueberry-Containing Pet Foods

A joint study conducted by the University of Guelph (Guelph, Canada), the University of Illinois (Urbana, Illinois) and Champion Petfoods Holdings (Morinville, Canada) investigated the polyphenol content in commercial dog and cat extruded food that lists blueberries on the ingredient deck. High-performance liquid chromatography (HPLC) determined that concentrations of free phenolics were minimal to nonexistent for all kibble types examined, determining kibble containing blueberries do not provide significant amounts of dietary polyphenols enhanced sources of antioxidants and anti-inflammation. A paper based on this research was published in the Journal of Animal Science (1).

Blueberries are an excellent source of polyphenols that provide antioxidant and anti-inflammatory benefits to humans and animals in a dose-dependent manner. Given that pet foods follow human food trends, blueberries are often included in cat and dog kibble as a source of antioxidants; however, the researchers report that there is little scientific evidence which supports this claim. However, given the dose-dependency of these compounds and the metabolic idiosyncrasies of dogs and cats, the impact of blueberry supplementation and functional dose should be assessed in each species separately (1).

Polyphenols are secondary metabolites located in the cell walls of plants which can be classified into five to six subcategories by structure (phenolic acids, stilbenes, flavonoids, lignans, tannins, and other polyphenols) (2) and can be bound to cell wall components (released through alkali hydrolysis) or unbound (free) (3). Sources of dietary polyphenols have been studied primarily for their antioxidant benefits across species in the past. Sled dogs fed blueberries before an exercise challenge, for example, showed an increase in total antioxidant power (TAP) when compared to a control group immediately following exercise; however, those effects were no longer observed 24 hours post-challenge (this is likely due to a short supplementation period [4-days] or perhaps a potentially low dose) (4).

The impact of dietary polyphenols on oxidation status has been researched in other species (for example, sheep, pigs, cattle, and poultry) and can be attributed to their ability to scavenge free radicals (5,6), increase vitamin E regeneration (7,8), inactivate metal ions (9), and inhibit pro-oxidizing enzymes (9–11). Focusing on blueberries because of their widespread growth across North America and use in the pet food market, the researchers hypothesized that dog and cat kibble will contain low levels of free and alkali-labile phenolics and quercetin, and that dog kibble would contain higher concentrations of all assessed polyphenol types than the cat kibble (1).

The researchers sampled 40 bags of kibble (18 cat and 22 dog) purchased from four pet food stores in Guelph, Canada. HPLC was used to determine the presence of quercetin, free phenolics and antioxidant-protected alkali-labile phenolics. Mean concentration +/- standard error (SE) was calculated for all assessed polyphenol types. The Analysis of Variance (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, with cat kibble having a lower average concentrations of both 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 (1).

From these findings, the researchers have reported that 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 antiinflammation. Future research should assess optimal polyphenol doses in healthy cats and dogs to determine the target doses to achieve physiological benefits, the researchers wrote (1).

References

1. Kosmal, P. A. L.; Dilger, R. N.; Bauer, L. et al. A "Berry" Small Inclusion: Forty Types of Commercial Dog and Cat Kibble with Added Blueberries Provide Low Levels of Quercetin, Free Phenolics, and Alkali-Labile Phenolics. J. Anim. Sci. 2025, skaf258. DOI: 10.1093/jas/skaf258
2. Li, A. N.; Li, S.; Zhang, Y. J. et al. Resources and Biological Activities of Natural Polyphenols. Nutrients 2014, 6 (12), 6020-6047. DOI: 10.3390/nu6126020
3. Beckman, C. H. Phenolic-Storing Cells: Keys to Programmed Cell Death and Periderm Formation in Wilt Disease Resistance and in General Defence Responses in Plants? Physiol. Mol. Plant Path. 2000, 57 (3), 101-110. DOI: 10.1006/pmpp.2000.0287
4. Dunlap, K. L.; Reynolds, A. J.; Duffy, L. K. Total Antioxidant Power in Sled Dogs Supplemented with Blueberries and the Comparison of Blood Parameters Associated with Exercise. Comp. Biochem. Physiol. A Mol. Integr. Physiol. 2006, 143 (4), 429-434. DOI: 10.1016/j.cbpa.2005.09.007
5. Alov, P.; Tsakovska, I.; Pajeva, I. Computational Studies of Free Radical-Scavenging Properties of Phenolic Compounds. Curr. Top. Med. Chem. 2015, 15 (2), 85-104. DOI: 10.2174/1568026615666141209143702
6. Pandey, K. B.; Rizvi, S. I. Ferric Reducing and Radical Scavenging Activities of Selected Important Polyphenols Present in Foods. Int. J. Food Prop. 2012, 15 (3), 702–708. DOI: 10.1080/10942912.2010.498547
7. Pazos, M.; Andersen, M. L.; Medina, I. et al. Efficiency of Natural Phenolic Compounds Regenerating Alpha-Tocopherol from Alpha-Tocopheroxyl Radical. J. Agric Food Chem. 2007, 55 (9), 3661-3666. DOI: 10.1021/jf063165l
8. Wu, H.; Bak, K. H.; Goran, G. V. et al. Inhibitory Mechanisms of Polyphenols on Heme Protein-Mediated Lipid Oxidation in Muscle Food: New Insights and Advances. Crit. Rev. Food Sci. Nutr. 2024, 64 (15), 4921-4939. DOI: 10.1080/10408398.2022.2146654
9. Gladine, C.; Rock, E.; Morand, C. et al. Bioavailability and Antioxidant Capacity of Plant Extracts Rich in Polyphenols, Given as a Single Acute Dose, in Sheep Made Highly Susceptible to Lipoperoxidation. Br. J. Nutr. 2007, 98 (4), 691-701. DOI: 10.1017/S0007114507742666
10. Hussain, T.; Tan, B.; Yin, Y. et al. Oxidative Stress and Inflammation: What Polyphenols Can Do for Us? Oxid. Med. Cell Longev. 2016, 2016, 7432797. DOI: 10.1155/2016/7432797