Y-Aminobutyric Acid

y-Aminobutyric acid (GABA), a four-carbon nonprotein amino acid, acts as the major inhibitory neurotransmitter of the central nervous system. GABA also has antihypertensive, diuretic and tranquilizer effects, and prevents diabetes (for review, see Fayed, 2014). GABA is produced by glutamate decarboxylase (GAD), which catalyzes the decarboxylation of glutamate to GABA. Glutamate and/or environmental stresses (e.g., acidity, osmotic and starvation) induce the GAD pathway of primary cheese starters, such as Lc. lactis, Streptococcus thermophilus and L. delbrueckii ssp. bulgaricus, nonstarter lactic acid bacteria (NSLAB) (e.g., Lactobacillus brevis, L. paracasei, Lactobacillus plantarum), and lactobacilli isolated from human and animal intestine (Gobbetti et al., 2010). Due to its physiological functions, several GABA-enriched dairy products have been manufactured. L. paracasei (Komatsuzaki et al., 2005), L. brevis (Inoue et al., 2003), Lc. lactis (Nomura et al., 1998), B. longum (Park and Oh, 2005), and Lactobacillus buchneri (Cho et al., 2007) were shown to synthesize GABA in culture media and/or in food matrices. Previously, several lactic acid bacteria were isolated from Italian cheeses and screened for GAD activity (Siragusa et al., 2007). Almost all the best GABA- producing strains were isolated from cheese varieties containing the highest concentration of GABA. Fermented milk products, such as yogurt, beyond their ability to be used as medium by GABA-producing gut or dairy strains, are fortified with GABA (ca. 200 mg GABA/kg) (Fayed, 2014).

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