Physical entrapment of glutamic acid decarboxylase from Lactobacillus casei IIB-09 in multifunctional mesoporous silica nanoparticles for controlled release of ɣ-aminobutyric acid in anxiety disorders

Gamma-aminobutyric acid (GABA) is a sedative drug capable of alleviating anxiety disorders, but its synthetic preparation is characterized by poor stability and insufficient bioavailability, along with its high cost. In this study, its precursor glutamic acid decarboxylase (GAD) from Lactobacillus casei IIB-09 was immobilized on biodegradable mesoporous silica nanoparticles (MSNPs) to improve the enzyme’s catalytic efficiency and bioavailability, while providing a cost-effective synthetic approach. Under optimized culture conditions, i.e., 0.5% (w/v) monosodium glutamate (MSG) at pH 6.5 for 48 h with an inoculum size of 2% (v/v), the highest GAD activity (3.59 ± 0.01 IU/mL/min) and concentration of GABA (137 ± 0.01 mM) were achieved. GAD was physically immobilized onto biodegradable MSNPs and subsequently characterized using various analytical techniques. To confirm the crystalline nature of MSNP, X-ray diffraction (XRD) analysis was performed. Further, UV–Vis, SEM, and FTIR spectra verified the immobilization of GAD on MSNPs. After optimization of the immobilization process, the immobilized enzyme showed a twofold increase in activity (2.59 ± 0.03 IU/mL). A comparative analysis was done to examine the thermophilic characteristics and the activity of both free and immobilized enzymes under varying concentrations of methanol and α-ketoglutarate. The free and immobilized GAD exhibited maximum GABA production (112 ± 0.02–119 ± 0.03 mM) at 45 °C. This study highlights the true potential of immobilized GAD as a sustainable approach for its efficient biotransformation into GABA for applications in the pharmaceutical and functional food industries.