Effects of copper source and supplementation level on degradation products, color, and fatty acid profile in canned pet food

Discolored thermally processed canned pet foods may be perceived by pet owners as moldy or adulterated. Interactions between trace minerals, especially copper, and fatty acids or carbohydrates may occur during canning. Today, copper is supplemented primarily as highly reactive, inorganically bound copper sulfate. Chelated copper sources may protect the metal ion and prevent formation of undesirable/visually unfavorable reactions. Therefore, the objective of this work was to determine the effects of 3 mineral premixes at 2 levels of inclusion in a canned pet food diet on color, degradation products, and fatty acid profile. In a 2ｘ3 + 1 augmented factorial arrangement of treatments, canned pet food diets were as follows: no mineral premix (NC), 60 mg/kg dry matter (DM) from copper-lysine-glutamate (LG60), copper amino acid complex (CA60), and copper sulfate (CS60), or 300 mg/kg DM from the same copper sources (LG300, CA300, and CS300, respectively). The copper supplementation levels represented roughly 8–12 and 41–60 times the minimum recommended allowances for adult dogs and cats [7.3 and 5.0 mg/kg DM, respectively; Association of American Feed Control Officials AAFCO (2017)]. Diets were produced in three 20-can batches over 3 days (replicates) and cooked in a still retort (Dixie; Athens, GA). All treatments were analyzed for copper, iron, zinc, manganese, thiamin, vitamin A, and vitamin E. Fatty acids were quantified for NC, CS60, LG60, and CA60. Color was analyzed by slicing the full canned product into 4 segments and measuring each portion with a colorimeter (CIELAB color system). Data were analyzed as a linear mixed model with significance set at P < 0.05. Fatty acids were not affected (P > 0.05) by copper source, nor were thiamin or vitamin A by concentration or source of copper. Vitamin E concentration of NC was greater (P < 0.05) than all other treatments. The control (NC), as a reference, was lighter, redder, and more yellow (P < 0.05) than all other treatments. Yellowness was not different (P > 0.05) between copper-supplemented treatments and LG300 was darker (P < 0.05) than LG60, CA60, and CS300 but did not differ (P > 0.05) from CS60 or CA300. This research indicated that all copper sources tested led to color change of canned pet food when over-supplemented. Further research is needed to determine if copper at lower levels might decrease discoloration to undetectable levels.