Transport and Mechanical Properties of High-ZT Mg2.08Si0.4−x Sn0.6Sb x Thermoelectric Materials

Mg₂(Si,Sn) compounds are promising candidate low-cost, lightweight, nontoxic thermoelectric materials made from abundant elements and are suited for power generation applications in the intermediate temperature range of 600 K to 800 K. Knowledge on the transport and mechanical properties of Mg₂(Si,Sn) compounds is essential to the design of Mg₂(Si,Sn)-based thermoelectric devices. In this work, such materials were synthesized using the molten-salt sealing method and were powder processed, followed by pulsed electric sintering densification. A set of Mg_2.08Si_0.4?x Sn_0.6Sb _x (0 ≤ x ≤ 0.072) compounds were investigated, and a peak ZT of 1.50 was obtained at 716 K in Mg_2.08Si_0.364Sn_0.6Sb_0.036. The high ZT is attributed to a high electrical conductivity in these samples, possibly caused by a magnesium deficiency in the final product. The mechanical response of the material to stresses is a function of the elastic moduli. The temperature-dependent Young’s modulus, shear modulus, bulk modulus, Poisson’s ratio, acoustic wave speeds, and acoustic Debye temperature of the undoped Mg₂(Si,Sn) compounds were measured using resonant ultrasound spectroscopy from 295 K to 603 K. In addition, the hardness and fracture toughness were measured at room temperature.     

Self-organized Ce(1-x)Gd(x)O(2-y) nanowire networks with very fast coarsening driven by attractive elastic interactions

Assembling arrays of ordered nanowires is a key objective for many of their potential applications. However, a lack of understanding and control of the nanowires' growth mechanisms limits their thorough development. In this work, an appealing new path towards self-organized epitaxial nanowire networks produced by high-throughput solution methods is reported. Two requisites are identified to generate the nanowires: a thermodynamic driving force for an unrestricted elongated equilibrium island shape, and a very fast effective coarsening rate. These requirements are met in anisotropically strained Ce(1-x)Gd(x)O(2-y) nanowires with the (011) orientation grown on the (001) surface of LaAlO(3) substrates. Nanowires with aspect ratios above ≈100 oriented along two mutually orthogonal axes are obtained leading to labyrinthine networks. A very fast effective nanowire growth rate (≈60 nm min(-1)) for ex-situ thermally annealed nanostructures derives from simultaneous kinetic processes occurring in a branched network. Ostwald ripening and anisotropic dynamic coalescence, both promoted by strain-driven attractive nanowire interaction, and rapid recrystallization, enabled by fast atomic diffusion associated with a high concentration of oxygen vacancies, contribute to such an effective growth rate. This bottom-up approach to self-organized nanowire growth has a wide potential for many materials and functionalities.     

Reduction of Listeria monocytogenes on frankfurters treated with lactic acid solutions of various temperatures

United States regulations require ready-to-eat meat and poultry processors to control Listeria monocytogenes using interventions which may include antimicrobials that reduce post-processing contamination by at least 1 log-cycle; if the treatment achieves ≥2 log reductions, the plant is subject to less frequent microbial testing. Lactic acid (LA) may be useful as a post-lethality intervention and its antimicrobial properties may increase with temperature of application. The aim of this study was to evaluate the effect of LA solution concentration and temperature on L. monocytogenes counts of inoculated frankfurters and to identify parameters (concentration, temperature, and time) that achieve 1 and 2 log-unit immediate reductions. Frankfurters were surface-inoculated with a 10-strain mixture of L. monocytogenes (4.4 ± 0.1 log CFU/cm²) and then immersed in distilled water or LA solutions (0–3%) of 4, 25, 40, or 55 °C for 0–120 s. A regression equation for L. monocytogenes reduction included significant (P < 0.05) effects by the terms of concentration, time, temperature, and the interaction of concentration and temperature; other tested parameters (other interactions, quadratic and cubic terms), within the experimental range examined, did not affect (P ≥ 0.05) the extent of reduction. Results indicated that the effectiveness of LA against L. monocytogenes, in addition to concentration, increased with solution temperature (in the range of 0.6–2.8 log CFU/cm²). The developed equation may allow processors to vary conditions of treatment with LA to achieve a 1 or 2 log-unit reduction of the pathogen and comply with United States regulations.     

Characterization of a multilayer film activated with Lactobacillus curvatus CRL705 bacteriocins

BACKGROUND: Bacteriocins produced by lactic acid bacteria offer enormous promise for food safety preservation. In this study an active multilayer film obtained by the incorporation of lactocin 705 and lactocin AL705, two bacteriocins produced by Lactobacillus curvatus CRL705 with antimicrobial activity against Lactobacillus plantarum CRL691 and Listeria innocua 7, respectively, was characterized for its potential application in active packaging technology. Film activity performance at different storage conditions, bacteriocins transfer into water and sunflower oil, and film surface properties were evaluated. RESULTS: Film activity against L. innocua 7 was maintained during 2, 4 and 6 weeks at 30, 10 and 5 °C respectively. At 30 and 10 °C, activity loss against L. plantarum CRL691 was observed on the second week of storage and after the fourth week at 5 °C. Results showed no significant difference for active multilayer film contact angle and seal properties compared to the control (without bacteriocins). A decrease in lactocin 705 inhibitory activity after sunflower oil contact was observed, while lactocin AL705 remained unaffected. After water contact, film activity was retained for both bacteriocins. CONCLUSIONS: As demonstrated by antimicrobial activity and physico‐mechanical properties retention, lactocin 705 and AL705 active multilayer film present potential for application in active packaging technology. Copyright © 2011 Society of Chemical Industry     

Incorporation of citrus fibers in fermented milk containing probiotic bacteria

The incorporation of Lactobacillus acidophilus CECT 903, Lactobacillus casei CECT 475 and Bifidobacterium bifidum CECT 870 together with lemon (LF) and orange (OF) fibers obtained from juice by-products were tested in (i) a model system: fiber enriched with de Man Rogosa Sharp (MRS) broth cultured with each probiotic bacteria and (ii) evaluation of populations of probiotic bacteria in fermented milks formulated with citrus fibers. Citrus fibers enhanced L. acidophilus CECT 903, and L. casei CECT 475 survival in MRS during refrigerated storage, whereas erratic results were obtained for B. bifidum CECT 870, OF enhanced its growth and LF had inhibitory effect. Populations of probiotic bacteria decreased with storage time in MRS broth. The presence of yogurt starter bacteria in probiotic fermented milks favored the growth and survival of L. acidophilus and B. bifidum. Citrus fiber presence in fermented milks also enhanced bacterial growth and survival of the tested probiotic bacteria. This study indicates that citrus fiber enriched fermented milk have good acceptability and are good vehicles for a variety of commercial probiotics but survival of B. bifidum will need to be improved.     

Consumer assessment of safety and date labeling statements on ready-to-eat meat and poultry products designed to minimize risk of listeriosis

Point-of-purchase safety-based labeling guidance on the proper storage and handling of refrigerated ready-to-eat (RTE) meat and poultry products could help reduce the risk of listeriosis. Seniors and pregnant women are two population groups at increased risk of listeriosis due to suppressed or compromised immune systems. We conducted 11 focus groups with senior-aged women and women of childbearing age in Colorado and Ohio to assess consumer awareness of Listeria, storage practices of RTE meat products, perceptions regarding the acceptability and usefulness of common date and potential food safety labeling statements on RTE meat and poultry products, and food safety information needs. Storage times for opened and unopened RTE products varied widely, with opened products often being stored longer than recommended. Women in both age groups paid attention to date labels on packages but varied highly in their interpretation of the statements. "Use by" statements were considered clearer and more helpful than "Sell by" or "Best if used by" labels. Proposed food safety-based labeling statements listing "antilisterial" agents used in RTE products were not well received. However, labels giving consumers instructions on how long they could keep RTE products and when to discard them after opening were considered helpful and well received. Participants indicated the need for further information about Listeria and its control. Educational information at point-of-purchase and where seniors and pregnant women congregate are suggested. Manufacturers are encouraged to provide more complete information on the safe storage and use of ready-to-eat meat and poultry products on package labels.     

植物乳杆菌发酵紫薯粉对酸面团面包的抗氧化特性及品质影响

采用紫薯粉和植物乳杆菌发酵紫薯粉制作富含花青素的面包,通过对比研究乳酸菌发酵紫薯粉对面包品质的影响;并探讨乳酸菌发酵紫薯粉对面包中花青素含量、总酚含量以及DPPH自由基清除率的影响。结果表明：相比紫薯粉面包,乳酸菌发酵紫薯粉使得面包pH值降低,总酸度(TTA)增加,面包比容有所减小,面包色度C*值增加而色相H*值减小,面包色泽由原来的浅紫色变为浅红色。感官评定的结果显示,采用紫薯粉或乳酸菌发酵紫薯粉制作的面包都为消费者所喜爱。同时,与紫薯粉面包相比,乳酸菌发酵紫薯粉面包的总酚含量和DPPH自由基清除率分别增加了90.8%和6.1%,增强了面包的抗氧化性。     

Inactivation of Salmonella during drying and storage of apple slices treated with acidic or sodium metabisulfite solutions

This study was undertaken to determine whether pretreating inoculated Gala apple slices with metabisulfite or acidic solutions enhanced the inactivation of Salmonella during dehydration and storage. Apple slices inoculated with a five-strain mixture of Salmonella (7.6 log CFU/g) were pretreated, dried for 6 h at 60 degrees C, and stored aerobically at 25 degrees C for 28 days. Predrying treatments included (i) no treatment, (ii) 10 min of immersion in sterile water, (iii) 10 min of immersion in a 4.18% sodium metabisulfite solution, (iv) 10 min of immersion in a 3.40% ascorbic acid solution, and (v) 10 min of immersion in a 0.21% citric acid solution. Samples were plated on tryptic soy agar with 0.1% pyruvate (TSAP), brilliant green sulfa (BGS) agar, and xylose lysine tergitol 4 (XLT4) agar for the enumeration of bacteria. Populations were not significantly (P > 0.05) reduced by immersion in water but were reduced by 0.7 to 1.1 log CFU/g by immersion in acidic solutions. Immersion in the sodium metabisulfite solution reduced populations by 0.4, 1.3, and 5.4 log CFU/g on TSAP, BGS agar, and XLT4 agar, respectively. After 6 h of dehydration at 60 degrees C, populations on untreated and water-treated slices were reduced by 2.7 to 2.8, 2.7 to 2.9, and 4.0 to 4.2 log CFU/g as determined with TSAP, BGS agar, and XLT4 agar, respectively. In contrast, populations on slices treated with sodium metabisulfite, ascorbic acid, and citric acid were reduced after 6 h of dehydration by 4.3, 5.2, and 3.8 log CFU/g, respectively, as determined with TSAP; by 4.7, 5.5, and 3.9 log CFU/g, respectively, as determined with BGS agar; and by 5.5, 5.7, and 5.6 log CFU/g, respectively, as determined with XLT4 agar. Bacteria were still detectable by direct plating after 28 days except on slices treated with ascorbic acid. Immersion in metabisulfite or acidic solutions prior to dehydration should enhance the inactivation of Salmonella during the dehydration and storage of Gala apple slices.     

Effect of steam cooking on distribution of paralytic shellfish toxins in different tissue compartments of scallops Patinopecten yessoensis

This study investigated the effect of steam cooking on distribution of paralytic shellfish poisoning toxins (PSP-toxins) in scallops Patinopecten yessoensis. Toxins analysis by high-performance liquid chromatography showed that most of the PSP-toxins (>70%) were accumulated in viscera and adductor muscle of the raw scallops. Steam cooking induced significant loss (p < 0.05) of PSP-toxins from viscera (16%), adductor muscle (24%), gill and mantle (11%) while 32% of the toxins were retained inside viscera and adductor muscle. Overall, 51% of PSP-toxins leaked out from scallop tissues during steam cooking. However, there was no significant loss (p > 0.05) of PSP-toxins from gonad. Consumption of viscera was the most significant risk factor for causing PSP, while gonad and scallop soup were the second most significant. A rapid PSP test further verified detectable levels of PSP-toxins in all samples. However, possible interfering substance(s) in adductor muscles and gonads might potentially affect the results from this test.