Suppression of hTAS2R16 Signaling by Umami Substances.

Interaction between umami and bitter taste has long been observed in human sensory studies and in neural responses in animal models, however, the molecular mechanism for their action has not been delineated. Humans detect diverse bitter compounds using 25-30 members of the type 2 taste receptor (TAS2R) family of G protein-coupled receptor. In this study, we investigated the putative mechanism of antagonism by umami substances using HEK293T cells expressing hTAS2R16 and two known probenecid-insensitive mutant receptors, hTAS2R16 N96T and P44T. In wild type receptor, Glu-Glu, inosine monophosphate (IMP), and l-theanine behave as partial insurmountable antagonists, and monosodium glutamate (MSG) acts as a surmountable antagonist in comparison with probenecid as a full insurmountable antagonist. The synergism with IMP of umami substances still stands in the suppression of hTAS2R16 signaling. In mutagenesis analysis, we found that Glu-Glu, MSG, and l-theanine share at least one critical binding site on N96 and P44 with probenecid. These results provide the first evidence for a direct binding of umami substances to the hTAS2R16 through the probenecid binding pocket on the receptor, resulting in the suppression of bitterness.

Conversion of agroindustrial residues for high poly(γ-glutamic acid) production by Bacillus subtilis NX-2 via solid-state fermentation.

Poly(γ-glutamic acid) (γ-PGA) production by Bacillus subtilis NX-2 was carried out through solid-state fermentation with dry mushroom residues (DMR) and monosodium glutamate production residues (MGPR; a substitute of glutamate) for the first time. Dry shiitake mushroom residue (DSMR) was found to be the most suitable solid substrate among these DMRs; the optimal DSMR-to-MGPR ratio was optimized as 12:8. To increase γ-PGA production, industrial waste glycerol was added as a carbon source supplement to the solid-state medium. As a result, γ-PGA production increased by 34.8%. The batch fermentation obtained an outcome of 115.6 g kg(-1) γ-PGA and 39.5×10(8) colony forming units g(-1) cells. Furthermore, a satisfactory yield of 107.7 g kg(-1) γ-PGA was achieved by compost experiment on a scale of 50 kg in open air, indicating that economically large-scale γ-PGA production was feasible. Therefore, this study provided a novel method to produce γ-PGA from abundant and low-cost agroindustrial residues.

Economical production of poly(γ-glutamic acid) using untreated cane molasses and monosodium glutamate waste liquor by Bacillus subtilis NX-2.

The production of poly(γ-glutamic acid) by Bacillus subtilis NX-2 from cane molasses and monosodium glutamate waste liquor (MGWL) was studied for the first time in this work. When batch fermentation was carried out with untreated molasses, 33.6±0.37 g L(-1) PGA was obtained with a productivity of 0.46±0.006 g L(-1) h(-1). In order to minimize the substrate inhibition, fed-batch fermentation was performed with untreated or hydrolyzed molasses in 7.5 L bioreactor, giving 50.2±0.53 and 51.1±0.51 g L(-1) of PGA at 96 h, respectively. Further studies were carried out by using MGWL as another carbon source, resulting in a PGA concentration of 52.1±0.52 g L(-1) with a productivity of 0.54±0.003 g L(-1) h(-1). These results suggest that the low-cost cane molasses and MGWL can be used for the environmental-friendly and economical production of PGA by B. subtilis NX-2.