In vitro bioaccessibility of inorganic and organic copper in different diets

In poultry diets, copper is an essential nutrient that is critical for various physiological functions. Although copper sulfate is commonly used due to its cost-effectiveness, organic copper sources are gaining popularity because of their superior production outcomes and environmental benefits. Nevertheless, understanding the distinct bioaccessibility of inorganic and organic copper in diverse dietary setting remains limited. This study investigated the bioaccessibility of copper sulfate, copper amino acid chelate, and copper proteinate in the intestine via in vitro digestion and in situ dialysis. The results showed significant differences in the molecular size distribution of compounds formed by different copper salts within the intestinal environment, thereby leading to varying bioaccessibility. Copper sulfate has a bioaccessibility of 47 % ± 4%, which is significantly lower than copper amino acid chelate and copper proteinate (63% ± 5%, and 60% ± 4%, respectively) in purified diet systems. Similarly, in whey protein systems, sulfate records 54% ± 10% bioaccessibility compared to 78% ± 9% and 76% ± 5% for copper amino acid chelate and copper proteinate. Coexisting feed ingredients have a significant impact on copper bioaccessibility. Copper sulfate forms precipitates, reducing its bioaccessibility to 34% ± 1% in sodium nitrate solution. The addition of digestive enzyme increases the bioaccessibility of copper sulfate to 81% ± 2% by providing organic ligands. Digestive enzyme also enhanced the bioaccessibility of copper proteinate from 36% ± 4% to 81% ± 4% by degrading its ligands. However, feed ingredients may decrease copper bioaccessibility by forming macromolecular complexes with copper, as all the organic ligands can competitively bind with copper in the intestine. These findings emphasize the importance of considering copper salt types and diet composition in animal nutrition practices.