Phytate and phytase: consequences for protein utilisation

Abstract

The excretion of large amounts of P in ef¯uent from intensive pig and poultry units is indicative of the poor availability of phytate-bound P in plant-derived feed ingredients. This environmental problem prompted the development and acceptance of microbial phytase feed enzymes for single-stomached animals. Their introduction led to an increasing recognition that phytate may have adverse effects on protein utilisation in addition to P. Consequently, the nutritional relevance of protein ±phytate interactions for pigs and poultry is considered in the present review. Since the current understanding of the effects of protein ±phytate interactions comes mainly from responses obtained to added phytase, literature on the in¯uence of microbial phytases on amino acid digestibility and utilisation is summarised, followed by a discussion of possible mechanisms contributing to the negative effects of phytate. However, the rationale for the protein responses to added phytase remains largely speculative, and several modes of action are probably involved. It may be that the release of protein from protein± phytate complexes occurring naturally in feed ingredients, the prevention of formation of binary and ternary protein ±phytate complexes within the gut, the alleviation of the negative impact of phytate on digestive enzymes and the reduction in endogenous amino acid losses are all contributing factors. A better understanding of the mechanisms of protein± phytate interactions and the modes of action of exogenous phytase enzymes is clearly desirable. Studies are also needed to identify and quantify the factors that contribute to the variable amino acid responses to added phytase. It appears that the relative solubilities of phytate salts and proteins from different feed ingredients and their effects on the extent of protein± phytate complex formation, coupled with variations in the effectiveness of phytase in different dietary contexts, may be the major factors responsible.

Nutritional geometry of calcium and phosphorus nutrition in broiler chicks. The effect of different dietary calcium and phosphorus concentrations and ratios on nutrient digestibility

“…Generally, as Na digestibility decreased the AID of amino acids was improved. Protein-phytate interactions are not completely understood, however, the benefits to protein digestibility from phytase are speculated to be derived from numerous factors (Selle et al, 2000). This is likely to be a combination of the release of protein from endogenous plant protein-phytate complexes, prevention of the formation of binary and ternary protein-phytate complexes within the intestine as well as the alleviation of negative phytate impacts on digestive enzyme and endogenous amino acids losses (Selle et al, 2012).…”

Extracellular phytase from Aspergillus niger CFR 335: purification and characterization

“…Phytic acid (myo-inositol hexakisphosphate) is the main storage form of phosphorus (P) in cereals, legumes and oilseeds. Depending on species, phytic acid constitutes 60-90 % of all phosphorus present in the grains (Selle et al 2000). Phytic acid covalently chelates metal ions such as Ca 2+ , Mg 2+ , Mn 2+ , Zn 2+ , Fe 3+ and proteins, rendering them insoluble and unavailable for absorption by monogastric animals (Erdman 1979;Erdman and Forbes 1981).…”

Enzyme Complex Added to Broiler Diets: Effects on Performance, Metabolizable Energy Content, and Nitrogen and Phosphorus Balance

“…As expected, the NC1 and NC2 diets effectively reduced N intake and N retention, when compared with the PC diet, demonstrating the beneficial effects of the protease present in the EC added to the diets. Previous studies reported that phytate may complex with the protein molecule as well as with amino acids (AA) and small peptides in the gastrointestinal tract (Selle et al, 2000). In addition, it significantly increases AA flow through the small intestine, resulting in higher endogenous AA excretion in broilers (Cowieson et al, 2004).…”