Screening and characterisation of gamma-aminobutyric acid (GABA) producing lactic acid bacteria isolated from Thai fermented fish (Plaa-som) in Nong Khai and its application in Thai fermented vegetables (Som-pak)
Gamma-aminobutyric acid (GABA) is a non-protein amino acid produced through the decarboxylation of glutamate by glutamate decarboxylase and wildly distributes among animals, plants and microorganisms (Ueno, 2000). GABA possesses well-known beneficial bioactivities such as neurotransmission, the induction of hypertension and a tranquilising effect (Pearl et al., 2006). On addition, it can stimulate immune cells (Dh et al., 2003) and is involved in the treatment of sleeplessness, depression and autonomic disorders (Dkada et al., 2000) as well as the improved prevention of diabetes (Hagiwara et al., 2004). This results in increasing commercial demand and extensive study to synthesis GABA in large amounts (Choi et al., 2006; Plokhov et al., 2000). However, the direct addition of GABA to food is considered unsafe and unnatural, while the utilisation of GABA-rich foods produced by natural techniques is more favourable (Dhakal et al., 2012). Many microorganisms are able to produce GABA, including bacteria, fungi and yeast. Among them, lactic acid bacteria (LAB) have been given more attention in research because of their utilisation in the food industry and the fact they are generally regarded as safe (GRAS) and known as probiotic. The production of GABA by LAB in fermented products can provide alternative, naturally fermented health products.