Influence of mineral source and inclusion levels of iron, copper, and zinc on the oxidative stability of extruded cat food

This study aimed to compare inorganic sources (sulfates) and chelated organic sources (proteinates) of minerals on the oxidative stability and shelf-life of extruded cat food. Five complete foods were formulated, including a negative control without supplementation of iron (Fe), copper (Cu), or zinc (Zn). The other formulations were obtained by supplementing the negative control formulation with these microminerals in organic or inorganic form at one (1x) or two (2x) times the FEDIAF (2021) requirement level for adult cats. The effects of supplementation on oxidative stability and shelf-life were determined before and after extrusion and during the 365-day storage period. The levels of fatty acids and synthetic antioxidants (BHA and BHT) were significantly lower after extrusion (P < 0.05). While inorganic and organic mineral sources did not differ, the negative control retained higher levels of fatty acids and synthetic antioxidants compared to mineral sources and levels. After extrusion, saturated, monounsaturated, and polyunsaturated fatty acids were reduced by 22.82% ± 1.8%, 22.91% ± 1.9%, and 19.32% ± 2.5%, respectively, with no mineral source and level effects. The Concentrations of synthetic antioxidants were significantly lower after extrusion, with a retention of 49.72% in the negative control and 35.09% ± 1.23% in the other treatments. Storage studies showed that fatty acids declined over time without significant treatment differences (P > 0.05). As expected, the most evident change was that of polyunsaturated fatty acids. Synthetic antioxidant levels also lowered during storage, with significant differences among treatments (P < 0.05). The highest losses were observed in formulations supplemented with inorganic sources. These differences affected peroxide value, which was influenced by both supplementation level and source. At the end of 365 days of shelf life, the peroxide value in foods supplemented with inorganic minerals was 92.3% (1×) and 49.7% (2×) greater than in foods with the same level of organic minerals. The negative control formulation had the lowest peroxide value among all treatments. From this data, we can conclude that the source of the microelements Fe, Cu, and Zn does not influence the oxidative stability of cat food during the extrusion process; however, the inorganic sources (e.g., sulfates) favor the oxidation during storage, which may be attenuated using less reactive, organic trace mineral sources, such as proteinates.