Occurrence of gluten in canned and dry grain-free commercial pet food.

In recent decades, anthropomorphism of companion animals has led to an increased inclusion into family units such that they are viewed as family members. The pet food manufacturers have responded to this culture shift with trendy diets that questionably align with animal health and physiology. They include the grain-free diet as one of the most well-known and advertise. Industries usually claim these products as high protein "ancestral diets" considered healthier than their grain inclusive counterparts, mainly represented by gluten. However, confirmed reports of gluten-sensitive enteropathy (GSE) are rare in dogs and proved only in certain breeds (i.e. Irish setters, Border terriers). Moreover, establishing a direct cause and effect relationship between the intake of a dietary component and a disease is challenging, not least because pet food is a complex mixture of nutrients which may interact with each other, but also because of potential cross-contamination of proteins from origins not mentioned on the label (i.e. wheat or other cereals). Given the above, the aim of the present study was to ascertain the absence of gluten residues in pet food samples marked as "grain-free" and "gluten-free" diets, to assess the reliability of manufacturer labelling. 15 commercial diets labelled as grain- or gluten-free and 2 commercial diets containing wheat were sampled. An analytical procedure was developed and applied to determine specific markers of wheat gluten, through liquid chromatography interfaced with mass spectrometry with high power of resolution. The results are expressed as mg of wheat flour type "00" present in 1 g of feed. The quantification limit (LOQ) obtained in the wheat flour for ion m/z 894.5043, z = 2, is 4 mg of wheat flour per gram of feed, that is, weighing fewer grams of wheat flour the quantifier ion is not detectable. Taking into account this calibration line and the LOQ obtained, the samples were prepared and analyzed using the HPLC-HRMS method developed. Quantifier ion in 14 out of 15 samples from grain- or gluten-free diet was <LOQ, meaning that gluten residues from wheat or other cereals were not detectable, while in 1 out 15 samples analyzed, 10 mg of wheat flour/g feed were measured (in control samples of 50.3 and 53.4 mg of wheat flour/g feed, respectively).