Enhanced stability and catalytic performance of immobilized phospholipase D on chitosan-encapsulated magnetic nanoparticles using oxidized dextran and glutaraldehyde as cross-linkers

Phospholipase D (PLD) is essential for the bioconversion of phosphatidylcholine (PC) to phosphatidylserine (PS), a process valuable in functional food and medicine. This study explores the stability and catalytic properties of PLD immobilized on chitosan-encapsulated magnetic nanoparticles (CMNPs), utilizing oxidized dextran (DX) and glutaraldehyde (Glu) as cross-linkers. The cross-linker concentration and immobilization time were optimized to assess their effects on PLD catalytic performance. PLD immobilized on CMNPs with DX (DX-CMNPs-PLD) exhibited optimal activity at pH 8.0 and 30 °C, retaining over 40 % activity after 14 cycles, while Glu-cross-linked PLD (Glu-CMNPs-PLD) retained approximately 65 %. DX-CMNPs-PLD demonstrated superior pH, temperature, and operational stability compared to free PLD. Additionally, the immobilized PLD was characterized using transmission electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. Kinetics parameters (V_max and K_m) of the immobilized PLD were also studied with free PLD serving as a control. Conformational analyses indicated a significant change in PLD's secondary structure, particularly in β-sheet content, which likely contributed to the enhanced stability and activity. These findings suggest a promising approach for PLD immobilization on CMNPs, with notable implications for biotechnological applications.