Optimization of culture conditions for gamma-aminobutyric acid production by newly identified Pediococcus pentosaceus MN12 isolated from 'mam nem', a fermented fish sauce.

This study was aimed to identify and optimize the culture conditions for gamma-aminobutyric acid (GABA) production by a lactic acid bacterium strain isolated from mam nem, a fermented fish sauce. Among the six isolates obtained from mam nem, the MN12 had the most potent GABA-producing capability. The strain was then identified to be Pedioccocus pentosaceus by employing MALDI-TOF-MS and phenylalanyl-tRNA synthase sequencing methods. The initial cell density of 5.106 CFU/mL, monosodium glutamate concentration of 60 mM, initial pH of 7, temperature of 45°C and cultivation time of 72 h were found to be the optimal culture conditions for highest production of GABA, reaching 27.9 ± 0.42 mM, by this strain. The cultivation conditions for GABA production by P. pentosaceus MN12 have been successfully optimized, providing a foundation for the development of fermented foods enriched with GABA.

Mango leaf extract incorporated chitosan antioxidant film for active food packaging.

Health hazards associated with usage of plastic films for food preservation demands for development of active films from non-toxic and antioxidant rich bio-sources. The reported work highlights the development, characterization and application studies of chitosan films enhanced for their antioxidant activity by mango leaf extract (MLE) incorporation. Effect of MLE variation (1-5%) on the morphology, optical nature, water exposure and mechanical characteristics of the chitosan-MLE composite films was studied. Increase in the MLE concentration resulted in films with increased thickness and decreased moisture content. Contact angle, water solubility and vapor permeability analysis demonstrated the reduced hydrophilicity and water vapor penetrability of the films due to MLE inclusion. MLE films possessed better tensile strength (maximum of 23.06 ±â€¯0.19 MPa) with reduced elongation ratio than the pure chitosan film (18.14 ±â€¯0.72 MPa). Antioxidants assessment in terms of total phenolic content, DPPH radical scavenging, ferric reducing power and ABTS radical scavenging showed improved antioxidant activity with the incremental amounts of MLE in the chitosan films. Microscopic studies revealed the smooth, compact and dense nature of the MLE-chitosan films favouring low oxygen transport rates. Application studies to cashew nuts preservation for 28 days storage indicated 56% higher oxidation resistance for the 5% MLE film than a commercial polyamide/polyethylene film. Results highlight the potential and promising nature of MLE impregnated chitosan films as suitable alternative for active packaging films for food preservation.

A density functional theory analysis for the adsorption of the amine group on graphene and boron nitride nanosheets.

In this paper first principles total energy calculations to study the adsorption of amine group (NH2) on graphene (G) and boron nitride (hBN) nanosheets are developed; the density functional theory, within the local density approximation and Perdew-Wang functional was employed. The sheets were modeled with a sufficiently proved CnHm-like cluster with armchair edge. The optimized geometry was obtained following the minimum energy criterion, searching on four positions for each nanosheet: perpendicular to the carbon atom, on the hexagon, inside the hexagon and on the bridge C-C, for the G-amine interaction; and, perpendicular to the B, perpendicular to the N, on the hexagon, and inside the hexagon, for the hBN-amine interaction. A physisorption, with amine parallel to the C-C-C bond with a distance graphene-amine of 2.56 Å, was found. For the case of BN a B-N bond, with bond length equal to 1.56 Å, was found; the amine lies perpendicular to the nanosheet. When the graphene is doped with B and Al atoms a chemisorption with B-N (1.57 Å) and Al-N (1.78 Å) bonds is observed; the bond angle in the amine group is also incremented, 5.5° and 8.1°, respectively. In the presence of point defects (monovacancies) of B in the hBN-amine and C in the G-amine, there exists chemisorption, increasing the reactivity of the sheets.

On the electronic properties of two-dimensional honeycomb GaInN and GaAlN alloys: a molecular analysis.

We have performed first principles total energy calculations to investigate the structural and the electronic properties of two-dimensional honeycomb GaAlN and GaInN alloys. Calculations were done using a coronene-like (C(24)H(12)) cluster and for different numbers of Ga, Al, and In atoms. The exchange and correlation potential energies were treated within the generalized gradient approximation (GGA). The bond length, dipole moment, binding energy, and gap between the HOMO and the LUMO are reported as a function of x. The stability of the structures depends on the site of the substituted atom; for example, when three Ga atoms are substituted, the GaInN alloy becomes unstable. The gap in the GaAlN increases from 3.76 eV (GaN) to 4.51 eV (AlN), and in the GaInN decreases to 2.11 eV. The biggest polarity occurs when eight and four Ga atoms are substituted, for GaAlN and GaInN, respectively.

Theoretical study of the electronic properties of fluorographene.

First-principles calculations were performed for fluorine-decorated graphene (fluorographene). Three different hexagonal clusters were used-circular (C(24)H(12)), triangular (C(23)H(10)) and rectangular (C(24)H(12))-and the fluorine atoms were randomly distributed in the mesh. Graphene is structurally stable in the three geometries, but fluorographene stability is only attained for the circular and triangular clusters. Gaps of the circular graphene and the corresponding fluorographene are 2.94 and 1.13 eV, respectively; in the triangular case, the values are zero and 0.47 eV. Both the circular and triangular structures show a transition from ionic to covalent character.