Cloning and heterologous expression of a glucodextranase gene from Arthrobacter globiformis I42, and experimental evidence for the catalytic diad of the recombinant enzyme

The gene encoding a glucodextranase from Arthrobacter globiformis I42 was cloned and, subsequently, heterologously expressed in Escherichia coli. This glucodextranase gene consists of 1048 amino acid residues with a calculated molecular mass of 109,135 Da. The roles of two residues at the active site of A. globiformis I42 glucodextranase were examined by site-directed mutagenesis. Glutamic acid residues 458 and 656, which are part of the apparent catalytic residues, were found to be essential for hydrolase activity.     

Monitoring of the multiple bacteriocin production by Enterococcus faecium NKR-5-3 through a developed liquid chromatography and mass spectrometry-based quantification system

Enterococcus faecium NKR-5-3 produces four antimicrobial peptides referred here as enterocins NKR-5-3A, B, C and D. A two-step electrospray ionization-liquid chromatography and mass spectrometry (ESI-LC/MS)-based quantification system was developed to monitor its multiple bacteriocin production profiles, which is essential in understanding the complex production regulation mechanism of strain NKR-5-3. The developed ESI-LC/MS-based quantification system can easily monitor the multiple bacteriocin production of this strain. Using the developed system, the production of enterocin NKR-5-3B was found to be not as variable as those of the other enterocins in different cultivation media. Production of enterocin NKR-5-3B was also found to have a wider optimum incubation temperature (20-30°C) than enterocins NKR-5-3A, C and D (25°C). Furthermore, at least 2?nM of the bacteriocin-like inducing peptide, enterocin NKR-5-3D, regulated the production of NKR-5-3 enterocins except enterocin NKR-5-3B. These findings taken together suggest that enterocin NKR-5-3B has an independent production regulation mechanism from the other NKR-5-3 enterocins. The developed system could effectively pin-point the production profiles of the multiple bacteriocins of E.?faecium NKR-5-3 under different fermentation conditions.     

A study of a two stage maximum power point tracking control of a photovoltaic system under partially shaded insolation conditions

A photovoltaic (PV) array shows relatively low output power density, and has a greatly drooping current–voltage (I–V) characteristic. Therefore, maximum power point tracking (MPPT) control is used to maximize the output power of the PV array. Many papers have been reported in relation to MPPT. However, the current–power (I–P) curve sometimes shows multi-local maximum point mode under non-uniform insolation conditions. The operating point of the PV system tends to converge to a local maximum output point which is not the real maximal output point on the I–P curve. Some papers have been also reported, trying to avoid this difficulty. However, most of those control systems become rather complicated. Then, the two stage MPPT control method is proposed in this paper to realize a relatively simple control system which can track the real maximum power point even under non-uniform insolation conditions. The feasibility of this control concept is confirmed for steady insolation as well as for rapidly changing insolation by simulation study using software PSIM and LabVIEW.     

Physicochemical Properties of Sweetpotato Starches with Different Gelatinization Temperatures

Physicochemical properties of five sweetpotato starches differing in gelatinization temperature were examined. The gelatinization temperature of Koganesengan starch, an ordinary cultivar of sweetpotato in Japan, was 73.6°C, whereas those of the other starches were measured to be 71.6°C for Kyukei 96162–1, 65.8°C for Kyushu No.127, 63.9°C for Kyukei 240, and 54.9°C for Quick Sweet. Some relationships of the primary structural properties with the gelatinization temperature have been found. As the gelatinization temperature decreased: i) the content of phosphate groups attached to the glucosyl residues decreased, ii) the amylose content, which was determined as difference in long chains of debranched original starch and of its amylopectin, decreased, iii) the proportion of unit chains with DP > 100 in the amylopectin fraction increased, iv) the proportion of unit chains with DP 6 to 10 in the amylopectin fraction increased, whereas that of unit chains with DP 12 to 24 decreased, v) the B‐type crystallinity of the starch granules was enhanced, and vi) the proportion of longer chains constituting each Nägeli amylodextrin increased. Moreover, it was found that thin pastes of the low temperature‐gelatinizing starches retrograded slower during cold storage than the ordinary starch. Among the starches, Quick Sweet starch granules, having the lowest gelatinization temperature, were digested rapidly by pancreatin.     

Phase Equilibria in the Pseudoternary System ZrO2−Y2O3−Cr2O3 at 1600°C in Air

The pseudoternary system ZrO₂-Y₂O₃-Cr₂O₃ was studied at 1600°C in air by the quenching method. Only one intermediate compound, YCrO₃, was observed on the Y₂O₃−Cr₂O₃ join. ZrO₂ and Y₂O₃ formed solid solutions with solubility limits of 47 and 38 mol%, respectively. The apex of the compatibility triangle for the cubic ZrO₂, Cr₂O₃, and YCrO₃ three-phase region was located at =17 mol% Y₂O₃ (83 mol% ZrO₂). Below 17 mol% Y₂O₃, ZrO₂ solid solution coexisted with Cr₂O₃. Cr₂O₃ appears to be slightly soluble in ZrO₂(ss).     

Interfacial tension of demixed polymer solutions over a wide range of reduced temperature

Interfacial tensions were measured for solutions of polystyrene-methylcyclohexane, polystyrene-heptamethylnonane and poly(dimethyl siloxane)-phenylethyl ether to investigate the behaviour of the interfacial tension from the critical point to a region far away from it. In the polystyrene-heptamethylnonane system, measurements were performed until the concentration of the polymer rich phase became about 70～80%. The molecular weight dependence of the interfacial tension was stronger away from the critical temperature than near to it. Data for polystyrene solutions with different solvents were connected by a scaling law. Recent scaling theories were compared with the results for poly(dimethyl siloxane) solution.     

Antibacterial activity of essential oil vapor for histamine-producing bacteria

In this study, we evaluated the antibacterial activity of essential oil vapors against histamine-producing bacteria Morganella morganii NBRC3848 and Raultella planticola NBRC3317. We measured the minimum inhibitory dose (MID) of 14 essential oils towards these two strains. Allyl isothiocyanate (AIT) and salicylaldehyde (SA) vapors showed higher antibacterial activity than the other 12 essential oil vapors. Both AIT and SA vapors suppressed growth of total aerobic bacteria and histamine-producing bacteria in bigeye tuna and mackerel meat during storage at 12°C. These vapors also inhibited histamine accumulation in bigeye tuna meat and mackerel meat. Thus, application of AIT and SA vapors is effective for preventing increase of histamine-producing bacteria and histamine formation in fish meat.     

Purification and properties of an ice-nucleating protein from an ice-nucleating bacterium, Pantoea ananatis KUIN-3

An ice-nucleating protein (INP) from the extracellular ice-nucleating matter (EIM) of Pantoea ananatis (Erwinia uredovora) KUIN-3 was purified and characterized. The EIM produced by the strain KUIN-3 was purified by ultrafiltration, sucrose density-gradient ultracentrifugation and gel filtration. The INP was purified using of column chromatography on hydroxyapatite and Superdex 200 in the nondenaturing detergent of 0.1% (w/v) Triton X-100. The purified INP was composed of one subunit of 117 kDa according to SDS-PAGE. It has become apparent that the INP was the ice-nucleating lipoglycoprotein based on the reaction of carbohydrate stain and lipid stain with the INP. It was inhibited by p-mercuribenzoate and N-bromosuccinimide. The activity of the INP gradually decreased from 65 degrees C. The pH stability was held between pH 7.0 and pH 11.0. The INP had a lower ice-nucleating temperature below pH 6.0. It has become apparent that the INP consisted of the class C structure in the EIM based on its freezing difference spectrum in D2O versus H2O.     

Control of amylase and protease activities in a phytase preparation by ampholyte-free preparative isoelectric focusing for unrefined cereal-containing bread

Direct addition of a food additive-grade Aspergillus niger phytase preparation to 30% brown rice flour-added bread ingredients reduced the bread myo-inositol hexaphosphate (IP₆) content. The phytase preparation had protease and amylase activities. Addition of the crude phytase preparation induced bread crust collapse. Protease-free high- and low-amylase phytase fractions were prepared using preparative ampholyte-free isoelectric focusing (autofocusing). Addition of the protease-free low-amylase phytase fraction did not significantly affect loaf volume and did not collapse the crust. Addition of the protease-free high-amylase phytase fraction significantly increased loaf volume approximately 1.5× in the presence of amylase at 193–1029 U. However, addition of 1029 and 2058 U of amylase induced partial and whole bread crust collapse, respectively. Therefore, removal of protease and control of amylase activities in the phytase preparation are crucial in the preparation of brown rice flour-added bread with a low myo-inositol phosphate (IP₆) and good swelling property.