Phytase Modulates Amino Acid and Mineral Ion Release Kinetics: Ingredient-Specific Responses in Plant Protein Ingredients

One of the most important antinutritional factors in plant-derived feeds is phytic acid (myo-inositol hexakisphosphate, IP6), which inhibits nutrient absorption in monogastric animals through a potent association with minerals, proteins, and digestive enzymes. Although exogenous phytase is widely used to improve phosphorus availability, its role in regulating the dynamic release of amino acids and mineral ions remains poorly understood. This study investigated the effects of phytase supplementation on IP 6 hydrolysis, mineral ion release, enzyme activity, and amino acid release kinetics across different plant protein ingredients using a controlled in vitro digestion model. The results showed that phytase supplementation significantly enhanced apparent IP 6 hydrolysis across all ingredients, with apparent hydrolysis approaching maximal levels at 500 U/kg. This was accompanied by increased solubilization of phosphorus and calcium, with clear dose-dependent responses in canola meal and plateau effects in soybean meal and corn gluten meal. Amino acid release exhibited different ingredient-dependent kinetic patterns, characterized by rapid-plateau responses in soybean and canola meals and a bimodal release pattern in corn gluten meal. Notably, kinetic parameters of amino acid release (D max and k) showed weak association with IP 6 hydrolysis, indicating that protein digestion is governed mainly by ingredient matrix characteristics rather than phytate degradation alone. Phytase primarily accelerated the timing of nutrient release without substantially increasing the total extent of protein hydrolysis. These results provide a mechanistic understanding of the kinetics of in vitro digestion and indicate ingredient-specific variations in nutrient release kinetics.