The Effects of Canning on the In Vitro Solubility of Phosphorus in Pet Food

Excess phosphate (P) intake through inorganic P (Pi) addition is known to cause various adverse health effects while declaration of use and amount in pet food in the EU is not regulated. Distinction between organic phosphate (oP) from feed ingredients and Pi with standard laboratory methods is impossible. Most Pi sources are highly soluble after 1 min in water (P_sol1). Measuring fractions of P according to solubility by the method of Lineva et al. (2019) can be used to estimate Pi addition. Heat processing reduces the fraction of P_sol1 in meat. The aim of this study was to investigate the effect of heat- and pressure processing on complete wet diets with Pi addition. An experimental cat diet with loaf-type consistency was prepared. One sample without additives, one with a complete mineral-vitamin premix without Pi to balance and 16 samples with such premixes plus Pi addition from four different commonly used sources (H₃PO₄, NaH₂PO₄*H₂O, KH₂PO₄, CaHPO₄) were tested in various combinations and concentrations. Ca/P ratios were adjusted in ranges between 1/1 and 2/1 and for three samples above 2/1. Part of the samples was kept raw and stored frozen, the rest was canned individually according to specifications common for the canning process. The samples were analysed by the method of Lineva et al. (2019), measuring fractions of soluble P in water and 0.4% HCl after 1 and 90 min in raw and canned samples. The results showed a strong correlation between Pi addition and measured amount of P_sol1 in the raw samples. However, P_sol1 strongly decreased in the identical canned samples. High amounts of P_sol1 are found in commercial pet food. The findings of this study indicate that the amount of added Pi in commercial pet food is probably even higher than can be expected by measuring P_sol1.