Characterization of spontaneous phage-resistant derivatives of Lactobacillus delbrueckii commercial strains

A total of 44 spontaneous phage-resistant mutants were isolated from three commercial Lactobacillus delbrueckii strains by secondary culture and agar plate methods. Phenotypic characteristics related to their phage-resistance capacities, i.e. plaquing efficiency, phage-resistance stability, lysogeny and adsorption rates were determined. The morphological, biochemical (sugar fermentation patterns) and technological (acidifying and proteolytic activities and acidification kinetics) properties of mutants were also studied. Amplification and restriction analysis of the 16S rRNA gene (PCR-ARDRA) was applied to confirm strain identity at the subspecies level. Random amplification of polymorphic DNA (RAPD-PCR) was used to determine genetic diversity among the isolates and their respective parent strains. The secondary culture method was the most useful for obtaining phage-resistant mutants. Phage resistance stability was a variable property among the isolates, but a high level of resistance was exhibited as quantified by the efficiency of plaquing. Furthermore, a total absence of spontaneous lysogeny was demonstrated. Adsorption rates were heterogeneously distributed among the three groups of mutants. All mutants isolated from two sensitive strains were similar to them with respect to technological properties. Two groups of mutants with distinctive technological properties were isolated from the other sensitive strain. PCR-ARDRA revealed that two out of three sensitive strains identified commercially as Lb. delbrueckii subsp. bulgaricus were actually Lb. delbrueckii subsp. lactis. Some of the phage-resistant mutants that were obtained might be used in culture rotation programs without regulatory restrictions when commercial strains become sensitive to phages present in industrial environments.     

Genes encoding bacteriocins and their expression and potential virulence factors of Enterococci isolated from wood pigeons (Columba palumbus)

Samples of the intestinal content and carcasses of wood pigeons (Columba palumbus) were evaluated for enterococci with antimicrobial activity. Enterococcus faecium comprised the largest enterococcal species with antagonistic activity, followed by Enterococcusfaecalis and Enterococcus columbae. PCR amplification of genes coding bacteriocins and determination of their nucleotide sequence, and the use of specific antipeptide bacteriocin antibodies and a noncompetitive indirect enzyme-linked immunosorbent assay, permitted characterization of enterococci coding that described bacteriocins and their expression. The efaAfm determinant was the only virulence gene detected in E. faecium, whereas E. faecalis showed a larger number of virulence determinants, and E. columbae did not carry any of the virulence genes examined. Although all E. faecalis isolates manifested a potent direct antimicrobial activity, no activity was detected in supernatants of producer cells. Purification of the antagonistic activity of E. columbae PLCH2 showed multiple chromatographic fragments after matrix-assisted laser desorption-ionization time-of-flight mass spectrometry analysis, suggesting the active peptide(s) had not yet purified to homogeneity. Bacteriocinogenic E. faecium and E. columbae isolates may be considered hygienic for production of enterocins and potentially safe due to their low incidence of potential virulence genes and susceptibility of most relevant clinical antibiotics. However, the presence among the enterococci of E. faecalis strains with a potent antagonistic activity and multiple virulence factors is an issue that must be considered further.     

A New Potential Attractant for Anastrepha obliqua from Spondias mombin Fruits

Nonirradiated males and females of Anastrepha obliqua (Macquart) were attracted to and landed more frequently on ripe fruits of Spondias mombin L. than on artificial fruit in wind tunnel bioassays. Porapak Q volatile extracts of S. mombin were also attractive and elicited landing on artificial fruit for both sexes. Combined gas chromatographic–electroantennographic detection (GC-EAD) analysis of volatile extracts showed that nine volatile compounds elicited repeatable antennal responses from females and males. The EAD-active compounds were identified by GC–mass spectrometry (MS) as follows: ethyl butyrate, isopropyl butyrate, hexan-1-ol, propyl butyrate, isobutyl butyrate, ethyl hexanoate, isopentyl butyrate, ethyl benzoate, and ethyl octanoate. In wind tunnel bioassays, males and females were attracted and landed more frequently on lures containing the nine-component blend of synthetic compounds than on unscented controls. Field cage bioassays showed that multilure traps baited with the nine-synthetic blend captured significantly more A. obliqua than traps baited with hydrolyzed protein or water.     

New Miscible Poly(ether imide)/Poly(phenyl sulfone) Blends

Summary: Blends of PEI and PPSU were prepared directly during the plasticization step of an injection molding process throughout the full composition range. The molded blends were transparent and showed a single glass transition and no dispersed phase by SEM. These characteristics did not allow the presence of a single miscibilized phase to be inferred unambiguously due to the very similar T_gs and refractive indices of the two components of the blends. Miscibility was inferred after close observation of the position, height and area of the enthalpy relaxation peak of the 50/50 blend. The modulus of elasticity and yield stress changed linearly with composition, leading to polymer materials with intermediate characteristics. The linearity was attributed to the lack of decrease in free volume induced by mixing and to the similar orientation of the components before and after mixing. The PPSU presence only slightly reduced the known tendency towards brittle fracture of PEI under notched impact conditions, but the presence of a single amorphous phase led to an expected ductile behavior of the blends close to that predicted by the single rule of mixtures.

Break stress (?) and break strain (○) of PEI/PPSU blends as a function of composition.     

Use of O3 and O3/H2O2 for degradation of organic matter from Bayer liquor towards new resource management: Kinetic and mechanism

Since the quality of bauxite resources has decreased and the organic carbon content has increased, different approaches are explored to remove the organic matter in alumina production. Advanced oxidative processes (AOPs) represent a possibility since they are widely used as an alternative for treating wastewaters to degrade organic pollutant molecules and in hydrometallurgy processes. For this reason, the goal of the project was the ozonation of Bayer liquor for organic matter removal. The ozone concentration was evaluated over time, as well as the H₂O₂ concentration and temperature. Results showed that the total organic carbon (TOC) removal achieved 19% in the most optimized condition with a kinetic rate of 0.0157 h⁻¹ –21.9 mg/L O₃, 0.05 mol/L H₂O₂ at 80°C. The colour of the liquor changed from dark brown to white-yellow, indicating that the size of the organic compounds had decreased. Also, 95.4% of degraded TOC formed CO₂, and almost 50% of the organic matter was oxalate compounds. The energy required for ozone production versus removed organic matter demonstrated that the technique proposed might be technically and economically feasible to be applied in the Bayer process. The study demonstrates the application of AOP in an extremely alkaline condition.     

Improving textural quality in frozen jalapeño pepper by low temperature blanching in calcium chloride solution

The effects of low temperature blanching in calcium chloride solution of jalapeño peppers prior to freezing, on firmness retention, pH, methanol, colour and calcium ions of the product, were evaluated by response surface methodology. Texture, methanol content and pH were affected by all of the variables studied (P = 0.05). The optimum response was obtained at temperatures of 63.3–66 °C, calcium chloride concentrations of 0.17–0.21 m , immersion time of 11.6–14.4 min, with a holding time after blanching of 56.6–66.1 min. Microscopic evaluation of the thawed pepper showed that blanching in CaCl₂ solution provided a protective effect in maintaining cell wall integrity.     

An autoassociative model of causal reasoning and causal learning: Reply to Van Overwalle's (1998) critique of Read and Marcus-Newhall (1993).

The authors respond to F. Van Overwalle's (see record 1997-38975-003) critique of the explanatory coherence (ECHO) model of causal reasoning (P. Thagard, 1992) and its application to social reasoning (S. J. Read & A. Marcus-Newhall; see record 1994-01615-001). Contrary to Van Overwalle's doubts about its possibility, a feedback model similar to ECHO that learns covariation information appropriately is presented. This model simulates Read and Marcus-Newhall's results and can also simulate findings from the causal learning literature. In contrast, because of limitations in feedforward networks, Van Overwalle can simulate many of Read and Marcus-Newhall's results only by making incorrect assumptions about their procedures. Further, the model presented handles several issues that Van Overwalle's cannot, such as asymmetries in reasoning between cause and effect, evaluation of explanatory coherence, and causal chains. Finally, limitations of feedforward models of causal reasoning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odour‐active compounds in mango (Mangifera indica L. cv. Corazón)

Simultaneous distillation–extraction combined with GC‐FID and GC‐MS were used to analyse volatile compounds from mango (Mangifera indica L. cv. Corazón) and to estimate the most odour‐active compounds in the fruit. The analyses led to the identification of 167 components, from which 128 were positively identified. The aroma‐active areas in the gas chromatogram were screened by the application of the aroma extract dilution analysis and by odour activity values. Eighteen odorants were considered as the most odour‐active compounds: (E)‐β‐damascenone, ethyl butanoate, (E,Z)‐nonadienal, ethyl 2‐methylpropanoate, (E)‐2‐nonenal, (E)‐β‐ionone, terpinolene, δ‐3‐carene, β‐caryophyllene, ethyl 2‐methylbutanoate, limonene, myrcene, linalool, γ‐octalactone, nonanal, methyl benzoate, 2,5‐dimethyl‐4‐methoxy‐3(2H)‐furanone and hexanal.