Reversible Covalent Immobilization of Cinnamaldehyde on Chitosan Films via Schiff Base Formation and Their Application in Active Food Packaging

[EN] In this work, cinnamaldehyde was reversibly anchored to chitosan films via imino-covalent bonding. The Schiff base was synthesized in solid phase employing neutralized chitosan films immersed in acidified 95 % (v/v) ethanolic solution in which the aldehyde was dissolved. The substitution degree (%) of cinnamaldehyde to the amine group was close to 70 %. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analysis revealed the formation of the chitosan-cinnamaldehyde Schiff base. The hydrolysis of the imino bond and subsequent release of cinnamaldehyde were studied after the films had been subjected to different combinations of temperature/time treatments simulating food preservation methods. The amount of aldehyde that remained covalently attached to the films was monitored by ATR-FTIR, and the substitution degree was determined by elemental analysis. Surface contact angle and colour parameters of cinnamaldehyde-imine-chitosan films and these films subjected to different treatments were also evaluated. The antimicrobial properties of chitosan-Schiff base films were tested in vitro against Staphylococcus aureus and Escherichia coli and in milk inoculated with Listeria monocytogenes. The antimicrobial activity varied depending on the treatment applied and consequently the degree of imino bond hydrolysis achieved and cinnamaldehyde released. Films of Schiff base-chitosan derivative subjected to different time/temperature treatments inhibited the growth of L. monocytogenes for 12 days under refrigeration conditions, which may extend the microbiological shelf life of such products. Sensory analysis of milk in contact with the films showed that a cinnamon smell does not cause any rejection among potential consumers. These novel films could be used in the design of antimicrobial food packaging and in various other technological areas where sustained-release systems are requiredThe authors wish to thank the financial support provided by the Spanish Ministry of Science and Innovation (project AGL2012-39920-C03-01) and Spanish Research Council (CSIC, JAE-Predoc L.H. fellowship).Higueras-Contreras, L.; Lopez-Carballo, G.; Gavara Clemente, R.; Hernández-Muñoz, P. (2015). Reversible Covalent Immobilization of Cinnamaldehyde on Chitosan Films via Schiff Base Formation and Their Application in Active Food Packaging. Food and Bioprocess Technology. 8(3):526-538. https://doi.org/10.1007/s11947-014-1421-8S52653883Abreu, F. O., Oliveira, E. F., Paula, H. C., & de Paula, R. (2012). Chitosan/cashew gum nanogels for essential oil encapsulation. Carbohydrate Polymers, 89(4), 1277–1282.Balaguer, M. P., Gómez-Estaca, J., Gavara, R., & Hernández-Muñoz, P. (2011a). Biochemical properties of bioplastics made from wheat gliadins cross-linked with cinnamaldehyde. Journal of Agricultural and Food Chemistry, 59(24), 13212–13220.Balaguer, M. P., Gómez-Estaca, J., Gavara, R., & Hernández-Muñoz, P. (2011b). Functional properties of bioplastics made from wheat gliadins modified with cinnamaldehyde. Journal of Agricultural and Food Chemistry, 59(12), 6689–6695.Belletti, N., Lanciotti, R., Patrignani, F., & Gardini, F. (2008). Antimicrobial efficacy of citron essential oil on spoilage and pathogenic microorganisms in fruit-based salads. Journal of Food Science, 73(7), M331–M338.Burt, S. (2004). Essential oils: their antibacterial properties and potential applications in foods—a review. International Journal of Food Microbiology, 94(3), 223–253.Cocchiara, J., Lalko, J., Lapczynski, A., Letizia, C. S., & Api, A. M. (2005). Fragrance material review on cinnamaldehyde. Food and Chemical Toxicology, 43(6), 867–923.Coma, V., Martial-Gros, A., Garreau, S., Copinet, A., Salin, F., & Deschamps, A. (2002). Edible antimicrobial films based on chitosan matrix. Journal of Food Science, 67(3), 1162–1169.Damodaran, S., & Kinsella, J. E. (1980). Flavor protein interactions. Binding of carbonyls to bovine serum-albumin: thermodynamic and conformational effects. Journal of Agricultural and Food Chemistry, 28(3), 567–571.dos Santos, J. E., Dockal, E. R., & Cavalheiro, E. T. G. (2005). Synthesis and characterization of Schiff bases from chitosan and salicylaldehyde derivatives. Carbohydrate Polymers, 60(3), 277–282.Doyle, M. P., & Beuchat, L. R. (2007). Food microbiology: fundamentals and frontiers. Washington: ASM Press.Fleming, D. W., Cochi, S. L., MacDonald, K. L., Brondum, J., Hayes, P. S., Plikaytis, B. D., Holmes, M. B., Audurier, A., Broome, C. V., & Reingold, A. L. (1985). Pasteurized milk as a vehicle of infection in an outbreak of listeriosis. New England Journal of Medicine, 312(7), 404–407.Foster, L. J. R., & Butt, J. (2011). Chitosan films are not antimicrobial. Biotechnology Letters, 33(2), 417–421.Gallstedt, M., & Hedenqvist, M. S. (2006). Packaging-related mechanical and barrier properties of pulp-fiber-chitosan sheets. Carbohydrate Polymers, 63(1), 46–53.Gill, A., & Holley, R. (2004). Mechanisms of bactericidal action of cinnamaldehyde against Listeria monocytogenes and of eugenol against L. monocytogenes and Lactobacillus sakei. Applied and Environmental Microbiology, 70(10), 5750–5755.Guinesi, L. S., & Cavalheiro, E. T. G. (2006). Influence of some reactional parameters on the substitution degree of biopolymeric Schiff bases prepared from chitosan and salicylaldehyde. Carbohydrate Polymers, 65(4), 557–561.Guo, Z. Y., Xing, R. E., Liu, S., Zhong, Z. M., Ji, X., Wang, L., & Li, P. C. (2007). Antifungal properties of Schiff bases of chitosan, N-substituted chitosan and quaternized chitosan. Carbohydrate Research, 342(10), 1329–1332.Gutierrez, J., Barry-Ryan, C., & Bourke, R. (2008). The antimicrobial efficacy of plant essential oil combinations and interactions with food ingredients. International Journal of Food Microbiology, 124(1), 91–97.Higueras, L., López-Carballo, G., Cerisuelo, J. P., Gavara, R., & Hernández-Muñoz, P. (2013). Preparation and characterization of chitosan/HP-beta-cyclodextrins composites with high sorption capacity for carvacrol. Carbohydrate Polymers, 97(2), 262–268.Holley, R. A., & Patel, D. (2005). Improvement in shelf-life and safety of perishable foods by plant essential oils and smoke antimicrobials. Food Microbiology, 22(4), 273–292.Hosseini, S., Zandi, M., Rezaei, M., & Farahmandghavi, F. (2013). Two-step method for encapsulation of oregano essential oil in chitosan nanoparticles: preparation, characterization and in vitro release study. Carbohydrate Polymers, 95(1), 50–56.Huang, Z.H., Wan, D.C. & Huang, J.L. (2001). Hydrolysis of Schiff bases promoted by UV light. Chemistry Letters, (7), 708–709.Inukai, Y., Chinen, T., Matsuda, T., Kaida, Y., & Yasuda, S. J. (1998). Selective separation of germanium (IV) by 2,3-dihydroxypropylchitosan resin. Analytica Chimica Acta, 371(2–3), 187–193.Ji, C., & Shi, J. (2013). Thermal-crosslinked porous chitosan scaffolds for soft tissue engineering applications. Materials Science and Engineering: C, 33(7), 3780–3785.Jin, X., Wang, J., & Bai, J. (2009). Synthesis and antimicrobial activity of the Schiff base from chitosan and citral. Carbohydrate Research, 344(6), 825–829.Junttila, J. R., Niemela, S. I., & Hirn, J. (1988). Minimum growth temperatures of Listeria monocytogenes and non-haemolytic Listeria. Journal of Applied Bacteriology, 65(4), 321–327.Kasaai, M. R., Arul, J., Chin, S. L., & Charlet, G. (1999). The use of intense femtosecond laser pulses for the fragmentation of chitosan. Journal of Photochemistry and Photobiology, A: Chemistry, 120(3), 201–205.Kirdant, A. S., Shelke, V. A., Shankarwar, S. G., Shankarwar, A. G., & Chondhekar, T. K. (2011). Kinetic study of hydrolysis of N-salicylidene-m-methyl aniline spectrophotomerically. Journal of Chemical and Pharmaceutical Research, 3(4), 790–796.Kuhn, J., Considine, T., & Singh, H. (2006). Interactions of milk proteins and volatile flavor compounds: implications in the development of protein foods. Journal of Food Science, 71(5), R72–R82.Li, X., Shao, T., Shi, Q., & Hu, M. (2013). A diaryl Schiff base as a photo- and pH-responsive bifunctional molecule. RSC Advances, 3(45), 22877–22881.Lovett, J., Francis, D. W., & Hunt, J. M. (1987). Listeria monocytogenes in raw milk: detection, incidence, and pathogenicity. Journal of Food Protection, 50(3), 188–192.Mohamad, A. (2013). Reactivity of base catalysed hydrolysis of 2-pyridinylmethylene-8-quinolinyl-Schiff base iron(II) iodide complexes: solvent effects. Chemické zvesti, 67(4), 464–476.Muhamad, S. G. (2011). First photolysis of benzidine Schiff base in non aqueous solvents. International Journal of Chemistry, 1(3), 142–145.Muriel-Galet, V., López-Carballo, G., Gavara, R., & Hernández-Muñoz, P. (2012). Antimicrobial food packaging film based on the release of LAE from EVOH. International Journal of Food Microbiology, 157(2), 239–244.Nazzaro, F., Fratianni, F., De Martino, L., Coppola, R., & De Feo, V. (2013). Effect of essential oils on pathogenic bacteria. Pharmaceuticals, 6(12), 1451–1474.Renault, F., Sancey, B., & Crini, G. (2009). Chitosan for coagulation/flocculation processes—an eco-friendly approach. European Polymer Journal, 45(5), 1337–1348.Sashiwa, H., & Aiba, S. I. (2004). Chemically modified chitin and chitosan as biomaterials. Progress in Polymer Science, 29(9), 887–908.Shahidi, F., Arachchi, J. K. V., & Jeon, Y. J. (1999). Food applications of chitin and chitosans. Trends in Food Science & Technology, 10(2), 37–51.Vallapa, N., Wiarachai, O., Thongchul, N., Pan, J. S., Tangpasuthadol, V., Kiatkamjornwong, S., & Hoven, V. P. (2011). Enhancing antibacterial activity of chitosan surface by heterogeneous quaternization. Carbohydrate Polymers, 83(2), 868–875.Wang, J. T., Lian, Z. R., Wang, H. D., Jin, X. X., & Liu, Y. J. (2012). Synthesis and antimicrobial activity of Schiff base of chitosan and acylated chitosan. Journal of Applied Polymer Science, 123(6), 3242–3247.Zivanovic, S., Chi, S., & Draughon, A. F. (2005). Antimicrobial activity of chitosan films enriched with essential oils. Journal of Food Science, 70(1), M45–M51

Antimicrobial Effectiveness of Lauroyl Arginate Incorporated into Ethylene Vinyl Alcohol Copolymers to Extend the Shelf-Life of Chicken Stock and Surimi Sticks

[EN] This study was designated to determine the antimicrobial effect of ethyl-N-alpha-dodecanoyl-l-arginate hydrochloride (LAE) incorporated into ethylene vinyl alcohol copolymers (EVOH) films on chicken stock and ready-to-eat surimi sticks. Firstly, the effect of LAE against Listeria monocytogenes and Escherichia coli was studied by using flow cytometry and scanning electron microscopy. Next, film-forming solutions of ethylene vinyl alcohol copolymers EVOH29 and EVOH44 (29 and 44 % molar percentage of ethylene, respectively) containing 0, 5 and 10 % w/w of LAE were cast into films. Several experiments were conducted to determine the antimicrobial activity of the films in vitro and also in vivo with the above-mentioned food products. The outcome of the tests showed a high impact on the viability of bacteria treated with LAE, with dramatic damage to the membrane. The films were able to inhibit the microbiota of the food products studied for 10 days under storage at 4 A degrees C, showing a significant antibacterial effect against L. monocytogenes and E. coli. These films show great potential as systems for sustained release of active molecules to improve the safety and quality of packaged food products.The authors acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness, project AGL2012-39920-C03-01, and fellowship funding for V. M.-G.Muriel Galet, V.; Lopez-Carballo, G.; Gavara Clemente, R.; Hernández-Muñoz, P. (2015). Antimicrobial Effectiveness of Lauroyl Arginate Incorporated into Ethylene Vinyl Alcohol Copolymers to Extend the Shelf-Life of Chicken Stock and Surimi Sticks. Food and Bioprocess Technology. 8(1):208-216. https://doi.org/10.1007/s11947-014-1391-xS20821681Adams MR & Moss MO (2008) Food microbiology. The Royal Society of Chemistry Cambrigde, UKAppendini, P., & Hotchkiss, J. H. (2002). Review of antimicrobial food packaging. Innovative Food Science and Emerging Technologies, 3(2), 113–126.Bakal G & Diaz A (2005) The lowdown on lauric arginate. Food quality(Feb./March), 60-61.Fellows PJ (2009) Food processing technology: principle and practice. Third edn.Guo, M., Jin, T., Wang, L., Scullen, O. J., & Sommers, C. (2014). Antimicrobial films and coatings for inactivation of Listeria innocua on ready-to-eat deli turkey meat. Food Control, 40, 64–70.Han JH (2013) Innovations in food packaging.Hawkins, D. R., Rocabayera, X., Ruckman, S., Segret, R., & Shaw, D. (2009). Metabolism and pharmacokinetics of ethyl N-alpha-lauroyl-L-arginate hydrochloride in human volunteers. Food and Chemical Toxicology, 47(11), 2711–2715.Higueras, L., Lopez Carballo, G., Hernandez Munoz, P., Gavara, R., Rollini, M., López Carballo, G., & Hernández Muñoz, P. (2013). Development of a novel antimicrobial film based on chitosan with LAE (ethyl-N)-dodecanoyl-l-arginate) and its application to fresh chicken. International Journal of Food Microbiology, 165(3), 339–345.Kilcast D & Subramaniam P (2000) The stability and shelf-life of food. Woodhead Publishing CambridgeMuriel-Galet, V., Lopez-Carballo, G., Gavara, R., & Hernandez-Munoz, P. (2012). Antimicrobial food packaging film based on the release of LAE from EVOH. International Journal of Food Microbiology, 157(2), 239–244.Muriel-Galet, V., López-Carballo, G., Hernández-Muñoz, P., & Gavara, R. (2013). Characterization of ethylene-vinyl alcohol copolymer containing lauril arginate (LAE) as material for active antimicrobial food packaging. Food Packaging and Shelf Life, 1, 10–17.Rodriguez, E., Seguer, J., Rocabayera, X., & Manresa, A. (2004). Cellular effects of monohydrochloride of L-arginine, N-alpha-lauroyl ethylester (LAE) on exposure to Salmonella typhimurium and Staphylococcus aureus. Journal of Applied Microbiology, 96(5), 903–912.Sallam, & Ibrahim, K. (2007). Antimicrobial and antioxidant effects of sodium acetate, sodium lactate, and sodium citrate in refrigerated sliced salmon. Food Control, 18(5), 566–575.Sung, S.-Y., Sin, L. T., Tee, T.-T., Bee, S.-T., Rahmat, A. R., Rahman, W. A. W. A., Tan, A.-C., & Vikhraman, M. (2013). Antimicrobial agents for food packaging applications. Trends in Food Science & Technology, 33(2), 110–123.Theinsathid, P., Visessanguan, W., Kruenate, J., Kingcha, Y., & Keeratipibul, S. (2012). Antimicrobial activity of lauric arginate-coated polylactic acid films against Listeria monocytogenes and Salmonella typhimurium on cooked sliced ham. Journal of Food Science, 77(2), M142–149

Evaluation of evoh-coated pp films with oregano essential oil and citral to improve the shelf-life of packaged salad

[EN] The aim of this study was to improve the present packaging of salad by combining modified atmosphere packaging with a new antimicrobial active bag consisting of PP/EVOH film with oregano essential oil or citral, with the purpose of extending shelf-life and reducing possible microbiological risks. The (O-2) and CO2 barrier properties of PP/EVOH, mechanical properties (Young's modulus, tensile strength and elongation at break) were determined and compared with those of standard PP films. Antimicrobial tests were carried out for enterobacteria, total aerobic counts, yeasts and moulds, and lactic acid bacteria and psychrotrophic bacteria, and the effect of the release of the antimicrobial agent on the sensory characteristics of the salads was also studied. The application of the EVOH coating results in an increase in the tensile resistance of the PP films and a reduction in the elongation at break. The results showed that microorganism counts bacteria decreased especially at the beginning of the storage period. OEO and CITRAL samples had reductions of 1.38 log and 2.13 log respectively against enterobacterias, about 2 log against yeasts and moulds. The total aerobic counts reduced 1.08 log with OEO and 1.23 log with CITRAL and the reduction of lactic acid bacteria and psychrotrophic was about 2 log. Citral-based films appeared to be more effective than materials containing oregano essential oil in reducing spoilage flora during storage time. Sensory studies also showed that the package with citral was the most accepted by customers at the end of the shelf-life. (C) 2012 Elsevier Ltd. All rights reserved,Authors thank the financial support of the Spanish Ministry of Economy and Competitiveness (Project AGL2009-08776 and V.M-G fellowships), EU (Nafispack project 212544), Generalitat Valenciana (J.P.C. fellowship) and Mr. Karel Clapshaw (translation services).Muriel Galet, V.; Cerisuelo, JR.; López Carballo, G.; Aucejo, S.; Gavara Clemente, R.; Hernández Muñoz, P. (2013). Evaluation of evoh-coated pp films with oregano essential oil and citral to improve the shelf-life of packaged salad. Food Control. 30(1):137-143. https://doi.org/10.1016/j.foodcont.2012.06.032S13714330

Gaia Data Release 2 Mapping the Milky Way disc kinematics

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than G(RVS) = 12 mag. Both samples provide a full sky coverage. Aims. To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. Methods. We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (sigma((omega) over bar)/(omega) over bar Results. Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U - V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. Conclusions. Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non-axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential.Peer reviewe

Gaia Data Release 2. Kinematics of globular clusters and dwarf galaxies around the Milky Way

AIMS: The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. METHODS: Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. RESULTS: Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the Milky Way of 9.1{_₂.₆⁺⁶·²} x 10¹¹ M⊙ based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. CONCLUSIONS: All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release

Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram

Context. The ESA Gaia mission provides a unique time-domain survey for more than 1.6 billion sources with G ≲ 21 mag. Aims. We showcase stellar variability in the Galactic colour-absolute magnitude diagram (CaMD). We focus on pulsating, eruptive, and cataclysmic variables, as well as on stars that exhibit variability that is due to rotation and eclipses. Methods. We describe the locations of variable star classes, variable object fractions, and typical variability amplitudes throughout the CaMD and show how variability-related changes in colour and brightness induce “motions”. To do this, we use 22 months of calibrated photometric, spectro-photometric, and astrometric Gaia data of stars with a significant parallax. To ensure that a large variety of variable star classes populate the CaMD, we crossmatched Gaia sources with known variable stars. We also used the statistics and variability detection modules of the Gaia variability pipeline. Corrections for interstellar extinction are not implemented in this article. Results. Gaia enables the first investigation of Galactic variable star populations in the CaMD on a similar, if not larger, scale as was previously done in the Magellanic Clouds. Although the observed colours are not corrected for reddening, distinct regions are visible in which variable stars occur. We determine variable star fractions to within the current detection thresholds of Gaia. Finally, we report the most complete description of variability-induced motion within the CaMD to date. Conclusions. Gaia enables novel insights into variability phenomena for an unprecedented number of stars, which will benefit the understanding of stellar astrophysics. The CaMD of Galactic variable stars provides crucial information on physical origins of variability in a way that has previously only been accessible for Galactic star clusters or external galaxies. Future Gaia data releases will enable significant improvements over this preview by providing longer time series, more accurate astrometry, and additional data types (time series BP and RP spectra, RVS spectra, and radial velocities), all for much larger samples of stars

Gaia Data Release 2 Observations of solar system objects

CONTEXT: The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations. AIMS: We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality. METHODS: To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP). RESULTS: The overall astrometric performance is close to the expectations, with an optimal range of brightness G ∼ 12 − 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G ∼ 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects

Gaia Data Release 2: The celestial reference frame (Gaia-CRF2)

Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars which define akinematically non-rotating reference frame in the optical domain. A subset of them have accurate VLBI positions which allow the axes of thereference frame to be aligned with the ICRF radio frame. Aims. We aim to describe the astrometric and photometric properties of the quasars selected to represent Gaia-CRF2, the celestial reference frame of Gaia DR2, and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia-CRF2 is materialised by the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G ' 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = 20 mag. Large-scale systematics are estimated to be in the range 20 to 30 μas. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame meeting the ICRS prescriptions, i.e. built only on extragalactic sources. In accuracy it matches the current radio frame realised in the ICRF but with a much higher density of sources in all parts of the sky except along the Galactic equator

Photoactivated chlorophyllin-based gelatin films and coatings to prevent microbial contamination of food products

[EN] The aim of this work was to develop antimicrobial photosensitizer-containing edible films and coatings based on gelatin as the polymer matrix. incorporating sodium magnesium chlorophyllin (E-140) and sodium copper chlorophyllin (E-141). Chlorophyllins were incorporated into the gelatin film-forming solution and the inhibiting effect of the cast films was tested against Staphylococcus aureus and Listeria monocytogenes. The results demonstrated that water soluble sodium magnesium chlorophyllin and water soluble sodium copper chlorophyllin reduced the growth of S. aureus and L monocytogenes by 5 log and 4 log respectively. Subsequently, the activity of self-standing films and coatings containing E-140 was assessed on cooked frankfurters inoculated with S. aureus and L monocytogenes. These tests showed that it was possible to reduce microorganism growth in cooked frankfurters inoculated with S. aureus and L monocytogenes by covering them with sodium magnesium chlorophyllin-gelatin films and coatings.The authors would like to thank I. Galdeano for technical support. They are also grateful for the financial support of the Generalitat Valenciana (Project GV04B-194) and the Spanish Ministry of Education and Science (project AGL2003-07326-C02-01).Lopez-Carballo, G.; Hernandez-Munoz, R.; Gavara Clemente, R.; Ocio, M. (2008). Photoactivated chlorophyllin-based gelatin films and coatings to prevent microbial contamination of food products. International Journal of Food Microbiology. 126(1):65-70. https://doi.org/10.1016/j.ijfoodmicro.2008.05.002S6570126

Modified sodium caseinate films as releasing carriers of lysozyme

[EN] Films made of sodium caseinate containing lysozyme where modified by chemical or biochemical crosslinkers to achieve a controlled release of the antimicrobial lysozyme. Kinetic studies in buffered solutions at pH 3.02-5.80 were undertaken. Both the pH and the use of crosslinkers had a strong effect on the protein network, and consequently, a significant influence on the releasing of lysozyme activity. Sodium caseinate (NaCas) films became insoluble networks at pHs close to the isoelectric point of caseinate (pH 4.6), therefore decelerating remarkably the diffusion of lysozyme without the addition of crosslinkers. Additionally a slow release of lysozyme was achieved after mixing with glyoxal, achieving a modulation in the antimicrobial activity against Micrococcus lysodeikticus and Staphylococcus aureus. Other crosslinkers, as calcium chloride or transglutaminase, almost blocked enzyme release and were not found adequate to achieve enough antimicrobial activity. Results showed that active caseinate films modified by pH and glyoxal efficiently retarded the release of lysozyme, being a promising way to extend antimicrobial effects during food storage and to enhance food safety. (C) 2009 Elsevier Ltd. All rights reserved.Authors thank the Spanish Comision Interministerial de Ciencia y Tecnologia for financial support under contract AGL07-65936-C02 and the Consolider Project Fun-C-Food CSD2007-00063 from the Spanish Ministry of Science an Innovation. P. M. de Souza thanks the Generalitat Valenciana for Grant number BFPI/2008/230. A. Fernandez thanks the Ramon y Cajal program from MICINN.Mendes De-Souza, P.; Fernandez, A.; Lopez-Carballo, G.; Gavara Clemente, R.; Hernández-Muñoz, P. (2010). Modified sodium caseinate films as releasing carriers of lysozyme. Food Hydrocolloids. 24(4):300-306. https://doi.org/10.1016/j.foodhyd.2009.10.005S30030624