Aroma profile of Niagara grape juice contaminated with multicoloured Asian lady beetle taint using gas chromatography/mass spectrometry/olfactometry

The objective of this study was to determine the odour‐active compounds present in Niagara grape juice tainted with multicoloured Asian lady beetle (MALB: Harmonia axyridis: Coleoptera: coccinellidae). Niagara grape juice was made with (2.5 MALB/L) and without MALB and evaluated using solid‐phase microextraction coupled with gas chromatography/mass spectrometry/olfactometry (GC/MS/O) to tentatively identify compounds. Compared to the control juice, phenol, described as musty/mouldy, was found to be unique to the MALB‐tainted grape juice. The four odourants significantly higher in the MALB‐tainted grape juice were described as fruity, asparagus, stagnant water/chemical and musty/mouldy, tentatively corresponding to octanal, 3‐sec‐butyl‐2‐methoxypyrazine (SBMP), 2‐methoxy‐4‐methylphenol and decanal, respectively. Three of the five compounds found in the MALB‐tainted juice have been reported to be produced by live MALB. While past literature has focused on the contribution of 3‐alkyl‐2‐methoxypyrazines to MALB‐taint, the present study suggests other compounds, in addition to SBMP, may contribute to the aroma profile of MALB‐tainted grape juice.     

Novel Lytic Enzyme of Prophage Origin from Clostridium botulinum E3 Strain Alaska E43 with Bactericidal Activity against Clostridial Cells

Clostridium botulinum is a Gram-positive, anaerobic, spore-forming bacterium capable of producing botulinum toxin and responsible for botulism of humans and animals. Phage-encoded enzymes called endolysins, which can lyse bacteria when exposed externally, have potential as agents to combat bacteria of the genus Clostridium. Bioinformatics analysis revealed in the genomes of several Clostridium species genes encoding putative N-acetylmuramoyl-l-alanine amidases with anti-clostridial potential. One such enzyme, designated as LysB (224-aa), from the prophage of C. botulinum E3 strain Alaska E43 was chosen for further analysis. The recombinant 27,726 Da protein was expressed and purified from E. coli Tuner(DE3) with a yield of 37.5 mg per 1 L of cell culture. Size-exclusion chromatography and analytical ultracentrifugation experiments showed that the protein is dimeric in solution. Bioinformatics analysis and results of site-directed mutagenesis studies imply that five residues, namely H25, Y54, H126, S132, and C134, form the catalytic center of the enzyme. Twelve other residues, namely M13, H43, N47, G48, W49, A50, L73, A75, H76, Q78, N81, and Y182, were predicted to be involved in anchoring the protein to the lipoteichoic acid, a significant component of the Gram-positive bacterial cell wall. The LysB enzyme demonstrated lytic activity against bacteria belonging to the genera Clostridium, Bacillus, Staphylococcus, and Deinococcus, but did not lyse Gram-negative bacteria. Optimal lytic activity of LysB occurred between pH 4.0 and 7.5 in the absence of NaCl. This work presents the first characterization of an endolysin derived from a C. botulinum Group II prophage, which can potentially be used to control this important pathogen.     

High‐pressure processing with hot sauce flavouring enhances sensory quality for raw oysters (Crassostrea virginica)

This study evaluated flavouring raw oysters by placing them under pressure in the presence of a commercially available hot sauce. Hand‐shucked raw oysters were processed at high pressure (600 MPa), in the presence or absence of hot sauce flavouring and evaluated by an experienced sensory panel 3 and 10 days after postharvest processing. The sensory panel evaluated high‐pressure‐processed oysters, with and without flavouring, for eleven flavours and three texture characteristics using an 11‐point intensity scale. Oysters were plump and characterised as moderately chewy and firm. Most oyster flavour characteristics were low in intensity with moderate intensity for briny and umami attributes. Flavoured oysters had a moderately intense tangy flavour and aftertaste. Flavouring a raw oyster by high‐pressure processing provides the potential to create a microbiologically safe product with unique sensory characteristics, which may influence consumer acceptance and marketability.     

GaAs TUNNETT diodes oscillating at 430-655 GHz in CW fundamental mode

GaAs TUNNET diodes with 75-nm thick undoped transit-time layer and 14-nm thick n/sup +/ electric-field-inducing layer were fabricated with molecular layer epitaxy. They were oscillating in fundamental-mode metal rectangular resonant cavities of WR-1.5 (0.381 /spl times/ 0.191 mm) and WR-1.2 (0.305 /spl times/ 0.152 mm) types. Continuous wave generation of -53 dBm to -49 dBm, in the frequency range of 430-510GHz, at the bias current from 500 to 560 mA was obtained in the WR-1.5 cavity. In the WR-1.2 cavity, CW generation in the range of 571-655 GHz was obtained with the bias current changing from 460 to 540 mA. Output power was -61dBm at 655 GHz. Frequency range of CW fundamental-mode TUNNETT diodes fabricated with molecular layer epitaxy extends from 60 GHz (+13 dBm) to 655 GHz.     

Molecular Characterization of a DNA Polymerase from Thermus thermophilus MAT72 Phage vB_Tt72: A Novel Type-A Family Enzyme with Strong Proofreading Activity

We present a structural and functional analysis of the DNA polymerase of thermophilic Thermus thermophilus MAT72 phage vB_Tt72. The enzyme shows low sequence identity (<30%) to the members of the type-A family of DNA polymerases, except for two yet uncharacterized DNA polymerases of T. thermophilus phages: φYS40 (91%) and φTMA (90%). The Tt72 polA gene does not complement the Escherichia coli polA⁻ mutant in replicating polA-dependent plasmid replicons. It encodes a 703-aa protein with a predicted molecular weight of 80,490 and an isoelectric point of 5.49. The enzyme contains a nucleotidyltransferase domain and a 3′-5′ exonuclease domain that is engaged in proofreading. Recombinant enzyme with His-tag at the N-terminus was overproduced in E. coli, subsequently purified by immobilized metal affinity chromatography, and biochemically characterized. The enzyme exists in solution in monomeric form and shows optimum activity at pH 8.5, 25 mM KCl, and 0.5 mM Mg²⁺. Site-directed analysis proved that highly-conserved residues D15, E17, D78, D180, and D184 in 3′-5′ exonuclease and D384 and D615 in the nucleotidyltransferase domain are critical for the enzyme’s activity. Despite the source of origin, the Tt72 DNA polymerase has not proven to be highly thermoresistant, with a temperature optimum at 55 °C. Above 60 °C, the rapid loss of function follows with no activity > 75 °C. However, during heat treatment (10 min at 75 °C), trehalose, trimethylamine N-oxide, and betaine protected the enzyme against thermal inactivation. A midpoint of thermal denaturation at T_m = 74.6 °C (ΔH_cal = 2.05 × 10⁴ cal mol⁻¹) and circular dichroism spectra > 60 °C indicate the enzyme’s moderate thermal stability.     

Tunneling through ultrathin GaAs n++-p++-n++ barrier grown by molecular layer epitaxy

The I-V characteristics of ultrathin GaAs n⁺⁺-p⁺⁺ -n⁺⁺ barrier structures with a 45 Å thick p⁺⁺ layer grown by molecular layer epitaxy (MLE) have been measured at room temperature and 77 K. The tunneling probability for this structure has been calculated as a function of effective tunneling width. It was found that good agreement between experiment and calculation is obtained when the effective tunneling width is assumed to be 75 Å, which is much smaller than the depletion width about 190 Å measured by C-V method. This fact indicates that the depletion width approximation cannot be used to measure the exact tunneling width for ultrathin barrier devices     

Ballistic and tunneling GaAs static induction transistors:nano-devices for THz electronics

GaAs static induction transistors (SIT) with 10-nm scale channel and with a 100-nm channel were fabricated with molecular layer epitaxy (MLE). Area-selective epitaxy of GaAs/AlGaAs/GaAs was used for the gate. Temperature dependence of current-voltage (I-V) characteristics of the 100-nm SIT indicates ballistic injection of electrons. In the 10-nm scale SIT, electrons are transported ballistically in the drain-side electric field. Direct tunneling is responsible for the transport through the potential barrier. It is indicated by the temperature dependence and by the electroluminescence spectrum. Electron transport in the 10-nm scale SIT is nearly scattering-free. The plausible estimation of the electron transit time is 2·10^-14 s; the worst case estimation based on saturated drift velocity gives 1·10^-13 s. It makes the ISITs suitable for THz applications. Multiple area-selective MLE GaAs regrowth was used as a tool for automatic definition of the channel length     

240-325-GHz GaAs CW fundamental-mode TUNNETT diodes fabricated with molecular layer epitaxy

Gallium arsenide (GaAs) transit-time diodes with tunnel injection of electrons (TUNNETT) with transit-time layer thickness of 100 and 150 nm were fabricated with molecular layer epitaxy (MLE). Continuous-wave fundamental-mode oscillation in the frequency range of 240 to 325 GHz in metal rectangular resonant 0.86 /spl times/ 0.43 mm size (WR-3) cavities was obtained. Output power of -13 dBm was generated at 322 GHz. The fundamental mode operation, as well as experiments on different impedance matching configurations, suggest that it is possible to develop fundamental mode TUNNETT generators for the frequency range of 350 GHz to 1 THz. Operation of the TUNNETTs confirms device quality of the MLE.