ISSUE FOCUS 60 FEED & ADDITIVE MAGAZINE May 2024 of chelated Zn as opposed to Zn sulfate diminishes, causing even numerically lower true absorption rates due to a small intestinal solubility of the chelates. CHELATED MINERALS STABILITY UNDER DIFFERENT PH CONDITIONS The stability of chelates can be severely affected by pH. An in silico simulation (Figure 2) represents a model of the copper-glycinate complex behavior in water at varying pH levels. Initially, before any interaction with water, copper is entirely bound to glycine in a stable complex. However, when the pH is lowered to 3, approximately 80% of copper becomes free ions (Cu2+), indicating reduced stability of the complex. On the contrary, at high pH levels, both the complex and precipitated forms equally make up 50% of copper, with no free ions present, suggesting a less reactive complex. The figure also shows that at pH 5.25, only 70% of the chelate is available, highlighting its decreased proportion as the pH decreases. This emphasizes the partial dissociation of chelates in acidic stomach conditions and potential chelate reformation or formation of other complex with organic molecules present in the higher pH environment of the small intestine. Based on the in silico simulation, our observations align with the findings reported by Byrne et al. (2021) for copper proteinates and Vacchina et al. (2010) for glycinates. For instance, Vacchina et al. (2010) illustrated an increase in metal-free glycine at acidic pH levels (below pH 5), with Fe-Gly appearing more stable during acidification compared to other glycinates (Cu, Zn, Mn). The graphs also indicated significant dissociation of these glycinates at pH below 4 to 5. The presence of glycinates in the intestinal tract leads to dissociation under acidic pH conditions, followed by chelation at basic pH, resulting in more than 100% of the initially added trace minerals in glycinates being present in the feed. Similarly, Byrne at al. (2021) revealed that proteinates are dissociated as soon as the pH drops below 6.5, with less than 50% of Cu-proteinates in the chelated form at pH <3.5. The key takeaway is that chelates, like other trace mineral sources, undergo dissociation at low pH and re-chelation at high pH. In the presence of free ions, there exists the potential for either the reformation of chelates or the creation of another complex with organic molecules in the higher pH environment of the small intestine. EFSA WEIGHS ON THE BIOAVAILABILITY OF CHELATED TRACE MINERALS Beyond considerations of pH stability, the bioavailability of chelated trace minerals has garnered attenOther Cu species Free Cu2+ ions Cu-Glycinate species pH Copper species proportions (%) Precipitated Cu species 100 90 80 70 60 50 40 30 20 10 0 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 Figure 2. In silico simulation of the proportion of copper chemical species relative to solution pH. The software Visual Minteq was used to determine the copper chemical species present at 25°C in a solution of 4.2 mM Cu-Glycinate and 0.1M NaNO3 at a pH range between 3 to 8 (authors).
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