Enhancement of γ-aminobutyric acid in fermented cucumbers

The effects of brine acidification, glutamate addition, and starter culture on γ-aminobutyric acid (GABA) content of fermented cucumber were investigated. GABA is a nonprotein amino acid with antihypertensive, antianxiety, and immunomodulatory properties. It is produced during cucumber fermentation but is limited by the low intrinsic concentration of free glutamate. Glutamine is 10-fold more abundant than glutamate in fresh cucumber and could provide additional substrate if converted to glutamate by glutaminase. Cucumbers were fermented in triplicate in acidified (pH 4.7-4.8) or nonacidified (pH 6.6) cover brines with 2% (342 mM) sodium chloride (NaCl) and 0 or 10 mM added glutamate. Indigenous and starter culture-assisted fermentations were conducted for each treatment at 28°C. The starter culture included lactobacilli containing gene sequences that encode for glutaminase (Lactobacillus gasseri ATCC 33323) and glutamate decarboxylase (Lactiplantibacillus plantarum WCFS1 ATCC BAA-793). GABA, glutamate, and glutamine were quantified by liquid chromatography triple quadrupole mass spectrometry. Both indigenous and starter culture-assisted fermentations effectively metabolized intrinsic and added glutamate, resulting in 10.4 ± 2.2 mM to 14.9 ± 0.7 mM GABA in glutamate supplemented fermentations compared with only 1.1 ± 0.2 mM in indigenous ferments. No additional increases in glutamate or downstream formation of GABA were observed in nonacidified brines with or without starter cultures, indicating that glutaminase production by L. gasseri and the indigenous microbiota was minimal or absent under these conditions. Glutamate addition to reduced salt cucumber fermentations generated ready-to-eat pickles that can deliver clinically relevant levels of GABA in a typical serving size. PRACTICAL APPLICATION: Research was conducted to explore ways to increase the production of the health-promoting compound, γ-aminobutyric acid (GABA), in fermented cucumber pickles. Cucumbers were fermented in reduced salt cover brines with or without added glutamate and/or acetic acid. Both natural and starter culture-assisted fermentations effectively converted the intrinsic and added glutamate to GABA, producing ready-to-eat pickles that can deliver clinically relevant levels of GABA in a typical serving size.