Abstract/Summary

γ-aminobutyric acid (GABA) is a non-protein amino acid which functions as an inhibitory neurotransmitter of the mammalian brain. orally administered GABA has tranquilizing and diuretic properties, and also relieves depression, anxiety, and most importantly reduce blood pressure. Due to its beneficial physiological functions research has focused on identification and isolation of bacterial strains producing high levels of GABA, which could be used in the production of fermented food products. This process is costly and labour intensive therefore, we developed a rapid colorimetric pre-screening test which could reduce costs in the isolation of GABA producers from various environments. Lactic acid bacteria (LAB) are the most important group of probiotics and starter cultures. Although fermented products are known sources of LAB, the human gut microbiota is also considered a good source as its natural habitat. However, isolates to be classified as probiotic, should be safe, withstand processes and exert a beneficial effect on the host. Therefore, various in-vitro tests were carried out to determine probiotic potential of isolated GABA producing strains. Lactobacillus plantarum strains showed similar characteristics with the reference strain Lactobacillus casei shirota which is a widely used probiotic. To increase the GABA levels in the gut of the host. high GABA producers could be delivered to the host through fermented products or apply dietary interventions that could increase GABA levels in the gut. We decided to investigate the 2nd strategy by using single stage, batch culture systems simulating the distal colon and also three-stage continuous colonic model system simulating the whole colon with inoculum from healthy donor. We focused on supplementing these systems with amino acids and peptides other than glutamate and look at a possible increase in GABA and SCFA levels. We found that amino acids (casamino acids, L-cysteine e.t.c), other than glutamate are able to increase gut microbiota mediated GABA and SCFA production in the colon. This suggests that increased consumption of protein –based food or dietary protein in our diets could possibly increase the production of GABA and SCFAs in the gut.