Unveiling the potential of two different lactococcal glutamate decarboxylase enzymes and their application for producing GABA-rich soy beverages

Gamma-aminobutyric acid (GABA) has been associated with health properties and has therefore attracted the attention of the food industry for the development of functional foods. Our previous studies elucidated the great capacity of Lactococcus lactis INIA Z108 strain, as well as the heterologous expression of the gadB gene from Lactococcus cremoris MG1363 in other strains to produce high yields of GABA. Because the biochemical properties of GadB enzymes from Lactococcus cremoris MG1363 and Lactococcus lactis INIA Z108 are still unknown, this study describes their characterization, stabilization on food-grade supports and their application for the production of plant-based beverages enriched in GABA. The recombinant GadB_MG1363 and GadB_Z108 enzymes were purified at yields of 18.12 and 20.53 mg per liter of culture, respectively. Both enzymes exhibited similar architecture and biochemical properties, exhibiting optimal activity at pH 5.0 and 40 °C, heat sensitivity at temperatures above 30 °C and similar catalytic efficiencies. Although multipoint covalent immobilization on agarose supports activated with N-hydroxysuccinimide groups drastically reduced the catalytic activity of both GadB enzymes, their stabilization was achieved by encapsulation in food-grade gellan gum. The resulting derivatives retained more than 70% of glutamate decarboxylase activity, improved their heat resistance to 50 ℃ and their tolerance to metal ions and higher pH levels. Since the application of these derivatives enabled the production of a non-fermented soy beverage enriched in GABA up to 9.27 mM, this study demonstrates the potential application of stabilized recombinant GadB enzymes for the production of GABA-enriched plant-based beverages.