Engineered phytases for emerging biotechnological applications beyond animal feeding

Phytases are important industrial enzymes able to catalyze the release of up to six phosphates from phytate in a stepwise hydrolysis reaction. Phytases are almost exclusively used as a feed supplement. However, phytases are also used in human nutrition, food processing, non-food industrial products, and emerging applications like enzymatic phosphate recovery from renewable resources. Phytate, the main phosphorus storage form in seeds, and its hydrolysis products act as a chelator and reduce protein and mineral bioavailability in intestinal absorption. Full phosphate hydrolysis from the common storage compound phytate remains a challenge. Phytate hydrolysis patterns of tailored phytases and their protein engineering campaigns are discussed. The aim of our review is to give an overview on developed and emerging application areas (animal nutrition, food processing, and environmental resource management) and thereby generate an awareness for the importance of phosphorus stewardship in a circular bioeconomy. Emphasis will be given to processes using organic-bound phosphorus and related recycling strategy of this valuable resource. In detail, the main challenge in designing phytases to completely hydrolyze phosphate from phytate to inositol and the need for engineering campaigns to broaden their industrial use are described.