Hierarchical Composites Promoting Immobilization and Stabilization of Phytase via Transesterification/Silification of Modulated Alginate Hydrogels

Microbial phytase as a feed additive could break down phytate in plant-derived feeds, thus rendering available phosphorus to animals and alleviate eutrophication pollution originated from their excreta. In the current study, an innovative hierarchical phytase immobilized composite was fabricated upon modulated alginate hydrogels by Fe3+ cross-linked sodium alginate (SA)/propylene glycol alginate (PGA)-xanthan gum (XG). According to enzyme activity assay, the composition of the ternary SA/PGA-XG biopolymer blend precursor was optimized to be at 0.05:1.5:1.0, wt %. The initially incorporated PGA as an alginate derivative could chemically immobilize phytase through an alkaline catalyzed transesterification reaction. Fe3+ active sites for cross-linking alginate hydrogels could concurrently immobilize Escherichia coli serine-phosphorylated phytase. After the micro hydrogen bubbles occurred within the internal microstructures of the hydrogels, the phytase immobilized ternary hydrogel templates were subjected to silification reactions. The finally fabricated phytase immobilized composites were endowed with reinforced mechanical strength and substrate diffusion properties. The median pore diameter (5.0 nm) was calculated according to mercury porosimetry. Nearly 94% of the original enzyme activity (182.5 U mg(-1)) could be preserved up to eight batch cycles. The as-prepared hierarchical composites were evidenced in promoting enzyme stability and residual activity, which provided more perspectives for sustainable animal agriculture at large-scale operations.