Simultaneous impact modified and chain extended glass fiber reinforced poly(lactic acid) composites: Mechanical,thermal, crystallization,and dynamic mechanical performance

Herein, glass fiber (GF) reinforced binary, ternary, and quaternary poly(lactic acid) (PLA) composites were prepared. Toughening, and chain extension of PLA was achieved through the incorporation of impact modifier and chain extender and their concurrent effects on the spectroscopic, crystallization, mechanical, thermal, and thermomechanical properties of the composites were investigated. High mechanical properties of GF influenced the mechanical performance of the composites. However, GF alone could not restrict the chain mobility of PLA due to poor interface and low crystallization activities in the PLA-GF composite. Incorporation of impact modifier and chain extender produced significantly enhanced interaction between GF and PLA. Significantly, the crystallinity, impact strength, and flexural modulus of PLA in the quaternary composite were increased by 58%, 63%, and 66%, respectively. In addition, damping and effectiveness coefficient of the PLA-GF composite were notably reduced by the simultaneous impact modification and chain extension of the reinforced composites.     

Selective binding of dye molecules and CdSe nanocrystals on nanostructures generated by AFM lithography of silicon surfaces

Anchoring optically active molecules or semiconductor nanocrystals on nanostructured surfaces is one of the first steps for building complex structures with variable properties and functions. Electrostatic interactions have been used for selective binding of cationic molecular species on lithographically generated and negatively charged nanostructures. Semiconductor nanocrystals, covered by amphiphilic molecules, have been bound via hydrophobic interactions. Selective binding of cationic Rhodamin 6G molecules to freshly prepared silicon oxide nanostructures as well as the CdSe/ZnS nanocrystals to the surrounding hydrophobic alkyl monolayer could be identified both by optical methods and by atomic force microscopy. The adsorption of CdSe/ZnS nanoparticles was accompanied by self-organization phenomena of the surfactant tri octyl phosphine oxide (TOPO).     

Atmosphere and blooming time affect color and lipid stability of frozen beef from steers supplemented with Vitamin E

The influence of blooming time (1, 6 or 48 h) and atmosphere (air or 100% oxygen) on color and lipid stability of frozen Longissimus lumborum (LL) from control and vitamin E supplemented steers was studied. Samples were stored at -20°C with or without illumination. Blooming control LL for 48 h in air followed by dark storage increased discoloration. Supplementation and blooming in oxygen, separately or combined, increased color display life. Illumination increased discoloration. Supplementation coupled with blooming for 6 or 48 h in 100% oxygen provided the highest color stability in both dark and illuminated storage. Color display lives for supplemented LL bloomed for 6 and 48 h in oxygen were 182 and 212 days for dark storage, and 21 and 73 days for illuminated display. Supplementation decreased lipid oxidation in illuminated LL, but blooming for 48 h in oxygen minimized this effect.     

Fast kd‐tree‐based hierarchical radiosity for radiative heat transport problems

In this paper we present a new efficient approach for radiative heat transfer simulations for various applications in engineering, combining existing approaches from different fields of computer science and heat transfer. For these application fields we assume radiative exchange between gray, diffuse surfaces in a radiatively nonparticipating medium. To solve the complex space–time behavior of radiation in 3D domains we use the hierarchical radiosity method. Here, the basic idea is to hierarchically subdivide surfaces forming a quad‐tree structure until a refinement criterion is reached. The fundamental underlying operation of the radiosity method is visibility detection which can be solved efficiently by using a space partitioning approach for the input surfaces. For this reason we choose a kd‐tree which is the best known acceleration structure for visibility detection on irregularly distributed surfaces. These approaches dramatically decrease the complexity of the radiation problem from n³ to O((k² + n)logk), where k is the number of input surfaces and n is the number of refined surfaces. We validate the approach for several non‐trivial examples and demonstrate that the scheme is second‐order accurate. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparative analysis of an intestinal strain of Bifidobacterium longum and a strain of Bifidobacterium animalis subspecies lactis in Cheddar cheese

Bifidobacteria cultures were incorporated into Cheddar cheeses to conduct a comparative analysis between the commercially available strain Bifidobacterium animalis ssp. lactis Bb-12 and the wild-type intestinal isolate, Bifidobacterium longum DJO10A. They were incorporated as starter adjuncts in separate vats and as a mixed culture, and survival through manufacturing and cheese ripening was assessed. For cheese using only Bb-12, the cells may have grown during cheese manufacture as 133% of the inoculum was incorporated into the cheese, resulting in 8.00 log cfu/g. Counts remained high during ripening showing less than 1 log decrease over a 12-mo period. For cheese using a mixed culture of Bb-12 and DJO10A, both strains were incorporated at much lower levels: 3.02 and 1.11%, respectively. This resulted in cheese with 6.00 and 5.04 log cfu/g for Bb-12 and DJO10A, respectively. Bifidobacteria survival rates were low, most likely due to the moisture of the cheese being below 38%. The Bb-12 demonstrated almost 100% viability during ripening. Numbers of DJO10A started to decline after 2 mo of ripening and dropped below the level of detection (2 log cfu/g) after 4.5 mo of ripening. Neither DJO10A nor Bb-12 fortified cheeses produced detectable amounts of organic acids during ripening other than lactic acid, indicating the lack of detectable metabolic contribution from bifidobacteria during cheese production and ripening such as production of acetic acid. To determine if sublethal stresses could improve the viability of DJO10A, 2 more vats were made, 1 with DJO10A exposed to sublethal acid, cold, and centrifugation stresses, and 1 exposed to none of these stresses. Although stress-primed DJO10A survived cheese manufacture better, as 72.8% were incorporated into the cheese compared with 41.1% of the unprimed, the statistical significance of this difference is unknown. In addition, the difference in moisture levels in the cheese cannot be excluded as influencing this difference. However, the rate of decline during ripening was similar for both. After 6 mo of ripening, cell counts in cheese were 4.68 and 4.24 log cfu/g for primed and unprimed cultures, respectively. These results suggest that whereas priming bifidobacteria with sublethal stresses before incorporation in a cheese fermentation may improve the number of viable cells that get incorporated into the cheese, it does not affect viability during cheese ripening.     

Activation Profile of TAS2R2, the 26th Human Bitter Taste Receptor

Scope

To avoid ingestion of potentially harmful substances, humans are equipped with about 25 bitter taste receptor genes (TAS2R) expressed in oral taste cells. Humans exhibit considerable variance in their bitter tasting abilities, which are associated with genetic polymorphisms in bitter taste receptor genes. One of these variant receptor genes, TAS2R2, is initially believed to represent a pseudogene. However, TAS2R2 exists in a putative functional variant within some populations and can therefore be considered as an additional functional bitter taste receptor.

Methods and results

To learn more about the function of the experimentally neglected TAS2R2, a functional screening with 122 bitter compounds is performed. The study observes responses with eight of the 122 bitter substances and identifies the substance phenylbutazone as a unique activator of TAS2R2 among the family of TAS2Rs, thus filling one more gap in the array of cognate bitter substances.

Conclusions

The comprehensive characterization of the receptive range of TAS2R2 allows the classification into the group of TAS2Rs with a medium number of bitter agonists. The variability of bitter taste and its potential influences on food choice in some human populations may be even higher than assumed.     

Hydroxy Acid Activation in Fungal Non-Ribosomal Peptide Synthesis Assessed by Site-Directed Mutagenesis

The fungal cyclodepsipeptides (CDPs) enniatin, beauvericin, bassianolide, and PF1022 consist of alternating N-methylated l -amino and d -hydroxy acids. They are synthesized by non-ribosomal peptide synthetases (NRPS). The amino acid and hydroxy acid substrates are activated by adenylation (A) domains. Although various A domains have been characterized thus giving insights into the mechanism of substrate conversion, little is known about the utilization of hydroxy acids in NRPSs. Therefore, we used homology modelling and molecular docking of the A₁ domain of enniatin synthetase (EnSyn) to gain insights into the mechanism of hydroxy acid activation. We introduced point mutations into the active site and used a photometric assay to study the substrate activation. The results suggest that the hydroxy acid is selected by interaction with backbone carbonyls rather than by a specific side chain. These insights enhance the understanding of non-amino acid substrate activation and could contribute to the engineering of depsipeptide synthetases.