			Home About us Contact

Test Substrates (test + substrate)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Evaluation of the Genotoxicity of Chitosan Nanoparticles for Use in Food Packaging Films

JOURNAL OF FOOD SCIENCE, Issue 6 2010
Renata De Lima
Abstract:, The use of nanoparticles in food packaging has been proposed on the basis that it could improve protection of foods by, for example, reducing permeation of gases, minimizing odor loss, and increasing mechanical strength and thermal stability. Consequently, the impacts of such nanoparticles on organisms and on the environment need to be investigated to ensure their safe use. In an earlier study, Moura and others (2008a) described the effect of addition of chitosan (CS) and poly(methacrylic acid) (PMAA) nanoparticles on the mechanical properties, water vapor, and oxygen permeability of hydroxypropyl methylcellulose films used in food packaging. Here, the genotoxicity of different polymeric CS/PMAA nanoparticles (size 60, 82, and 111 nm) was evaluated at different concentration levels, using the,Allium cepa,chromosome damage test as well as cytogenetic tests employing human lymphocyte cultures. Test substrates were exposed to solutions containing nanoparticles at polymer mass concentrations of 1.8, 18, and 180 mg/L. Results showed no evidence of DNA damage caused by the nanoparticles (no significant numerical or structural changes were observed), however the 82 and 111 nm nanoparticles reduced mitotic index values at the highest concentration tested (180 mg/L), indicating that the nanoparticles were toxic to the cells used at this concentration. In the case of the 60 nm CS/PMAA nanoparticles, no significant changes in the mitotic index were observed at the concentration levels tested, indicating that these particles were not toxic. The techniques used show promising potential for application in tests of nanoparticle safety envisaging the future use of these materials in food packaging. [source]

Potential for 4- n -nonylphenol biodegradation in stream sediments

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008
Paul M. Bradley
Abstract The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three hydrologically distinct streams impacted by wastewater treatment plants (WWTPs) in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring- 14C]4- n -nonylphenol (4- n -NP) as a model test substrate. Microcosms prepared with sediment collected upstream of the WWTP outfalls and incubated under oxic conditions showed rapid and complete mineralization of [U-ring- 14C]4-n-NP to 14CO2 in all three systems. In contrast, no mineralization of [U-ring- 14C]4- n -NP was observed in these sediments under anoxic (methanogenic) conditions. The initial linear rate of [U-ring- 14C]4- n -NP mineralization in sediments from upstream and downstream of the respective WWTP outfalls was inversely correlated with the biochemical oxygen demand (BOD) of the streambed sediments. These results suggest that the net supply of dissolved oxygen to streambed sediments is a key determinant of the rate and extent of 4-NP biodegradation in stream systems. In the stream systems considered by the present study, dissolved oxygen concentrations in the overlying water column (8,10 mg/L) and in the bed sediment pore water (1,3 mg/L at a depth of 10 cm below the sediment,water interface) were consistent with active in situ 4-NP biodegradation. These results suggest WWTP procedures that maximize the delivery of dissolved oxygen while minimizing the release of BOD to stream receptors favor efficient biodegradation of 4-NP contaminants in wastewater-impacted stream environments. [source]

In vitro evaluation of sun protection factors of sunscreen agents using a novel UV spectrophotometric technique

INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 4 2008
M. D. Bleasel
Synopsis A method for the in vitro determination of low- and high-value sun protection factors (SPF) of sunscreens using artificial substrates and a novel pseudo double beam (PDB) mode of operation of a standard double beam UV spectrophotometer is described. The method allows transmittance to be calculated from detector responses of reference and sample beams measured at different gain levels and facilitates the accurate quantification of low levels of electromagnetic radiation transmitted through highly absorbing samples. The spectrophotometer was modified to hold quartz diffusing plates on which a substrate [TransporeÔ adhesive tape or human stratum corneum obtained from a skin surface biopsy (SSB)] and the sunscreens to be tested were applied. The PDB mode of operation increased the effective linear range of the detector response of the spectrophotometer by a factor of approximately 20000-fold, enabling the in vitro SPF determination technique to be applied to both high and low SPF value sunscreens. Eight commercial sunscreens with known SPF values ranging from 4 to 77, previously determined by in vivo methods, were tested in vitro using both test substrates and correlations between the in vivo and in vitro values were determined. SPF values determined using the in vitro method correlated well with the known in vivo results (TransporeÔ tape, R2 = 0.611; SSB, R2 = 0.7928). The in vitro SPF obtained for one of the tested products differed substantially from the cited in vivo SPF value. Independent in vitro and in vivo re-evaluation of the SPF of this product matched the value predicted by the present method much more closely than the originally cited in vivo value. All determined SPFs were ordered correctly in comparison to in vivo ranking and the technique appeared to correctly identify a sunscreen that had a labelled SPF value that was significantly higher than its true SPF. Résumé Une méthode destinée à déterminer in vitro les facteurs de protection solaire (SPF) d'écrans solaires de faible et haut indice est décrite. Elle met en ,uvre des substrats artificiels et un nouveau mode opératoire reposant sur l'utilisation du pseudo double faisceau (PDB) d'un spectrophotomètre UV double faisceau standard. La méthode permet le calcul de la transmittence à partir des réponses du détecteur de référence et la mesure en simple faisceau à différents niveaux de gain facilitant ainsi la quantification précise des faibles niveaux de radiation électromagnétique (EMR) transmis à travers des échantillons hautement absorbants. Le spectrophotomètre a été modifié de façon à fixer des plaques diffusantes en quartz sur lesquelles un substrat (ruban adhésif Transport TM ou du stratum corneum humain obtenu à partir de biopsie de surface de peau (SSB) et les écrans solaires testés ont été appliqués. Le mode opératoire PTB augmente la gamme linéaire effective de la réponse du détecteur du spectrophotomètre d'un facteur approximatif 20.000 permettant, à cette technique de détermination des SPF in vitro, d'être appliquée à la fois sur les écrans solaires de haut et bas SPF. Huit écrans solaires commerciaux de SPF connus allant de 4 à 77, préalablement déterminés par des méthodes in vivo, ont été testés in vitro en utilisant les deux substrats, et les corrélations entre les valeurs in vivo et in vitro ont été déterminées. Les valeurs SPF déterminées en utilisant la méthode in vitro est bien corrélée avec les résultats in vivo connus (ruban transport, R2 = 0.611; SSB, R2 = .7928). Le SPF in vitro pour l'un des produits testés diffère fortement des valeurs SPF citées in vivo. Une réévaluation indépendante des SPF in vitro et in vivo de ce produit ajuste la valeur prédite par la présente méthode de façon beaucoup plus proche que la valeur originale citée in vivo. Tous les SPF ainsi déterminés sont ordonnés correctement en comparaison au classement in vivo et la technique semble identifier correctement un écran solaire qui possède un SPF libellé significativement plus haut que son vrai SPF. [source]

Insights into Sequence,Activity Relationships amongst Baeyer,Villiger Monooxygenases as Revealed by the Intragenomic Complement of Enzymes from Rhodococcus jostii RHA1

CHEMBIOCHEM, Issue 7 2009
Claudia Szolkowy
Abstract TheRhodococcus jostiiRHA1 genome encodes a number of enzymes that can be exploited as biocatalysts. Study of the substrate spectrum and enantioselectivity of Baeyer,Villiger monooxygenases from R. jostii allowed the identification of short amino acid sequences specific to groups displaying certain catalytic characteristics. The gel illustrates the substrate acceptance spectra and selectivities of the different proteins. Microbial genome sequences are providing a wealth of information on new enzymes that have considerable potential as biocatalysts. The recently sequenced genome of Rhodococcus jostii RHA1, for example, has revealed an impressive array of catabolic enzymes, including many putative Baeyer,Villiger monooxygenases (BVMOs). We have cloned 23 target BVMO sequences from the genome of R. jostii RHA1 and heterologously expressed 13 of these as soluble proteins to unearth new substrate specificities and selectivities. Whole-cell biocatalysts expressing the genes were screened against seven different test substrates. Each of these catalysts displayed activity toward at least three ketones. We observed a remarkable diversity of both regio- and enantioselectivity among the BVMOs from R. jostii RHA1 for the transformation of two chiral substrates, with some enzymes displaying high enantioselectivity for the isomers of 2-methylcyclopentanone. With the notable exception of the product of gene ro03437, named MO14, the biocatalysts' sequences correlated well with their respective activities and selectivities. This correlation allowed the identification of sequence motifs specific to subgroups of the BVMOs from R. jostii and other organisms. Overall, the data improve predictive models of BVMO activity from sequence and suggest new avenues to pursue in engineering these enzymes. [source]