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Salmonella is one of the main microorganisms that causes food-borne illnesses worldwide, although there are standard procedures to determine its presence or absence in food samples. However, these ...

Chia (Salvia hispanica L.) seeds contain antioxidants with great benefits for health and are widely used in the food industry. Antioxidants can be degraded by environmental factors, decreasing their biological activity. Their encapsulation in chitosan (CH) particles represents an alternative to protect them and increases their application. The encapsulation efficiency (%EE) of the antioxidants in the CH particles depends on the synthesis conditions. In this study, two methods for encapsulation of chia extract in chitosan particles were evaluated: method A, 0.05% CH in 1% acetic acid was mixed with 0.07% of tripolyphosphate (TPP) and method B, 0.3% CH in 2% acetic acid was mixed with 1% TPP. The results showed that the %EE decreased with the concentration of the extract, and the FTIR analysis suggested that the compounds of the extract were adsorbed on the surface of the particles. Dynamic light scattering and zeta potential analysis showed that the particles of method A are unstable and with a tendency to agglomerate, and the particles of method B are stable. The highest %EE was obtained with 0.2 mg·mL−1 (method A) and 1.0 mg·mL−1 (method B) of the extract. The higher loading capacity (%LC) (16–72%) was exhibited by the particles of method A. The best particle yield (62–69%) was observed for method B. The particles with the extract adsorbed showed antioxidant activity (5–60%) at 25°C; however, in the particles with the extract encapsulated, the activity increased after subjecting to acidic conditions at 40°C due to the breakdown of the particles. The results obtained will allow choosing the appropriate conditions for the synthesis of chitosan particles loaded with chia extracts with specific characteristics (%EE, %LC, size, and type) according to their future applications. The particles could be used in food and pharmaceutical industries and even in edible films for food packaging.

The water vapor permeability (WVP) and hardness of biodegradable nanocomposite films based on glutelin from Jatropha curcas L. were determined and the results were analyzed by response surface meth...

Physalis ixocarpa Brot. ex Hornem. and Physalis angulata L. are two edible species of the family Solanaceae, which have an important variety of antioxidant compounds present in their roots, stems, ...

A practical method to determine Staphylococcus aureus using bioconjugated gold nanoparticles is reported. The protocol uses gold nanoparticles stabilized by tetramethylrhodamine isothiocyanate labeled streptavidin followed by functionalization with biotinylated anti-staphylococcus aureus antibodies. The streptavidin stabilized gold nanoparticles were obtained by titration and analyzed by ultraviolet-visible spectroscopy and transmission electron microscopy. The obtained fluorescent bioconjugate selectively linked to the surface of S. aureus in samples contaminated with the microorganism, as demonstrated by confocal micrographs. The biorecognition process was performed by mixing the fluorescent bioconjugate with the sample. Bacterial dilutions from 1 × 108 to 1 × 102 cell/ml of S. aureus were determined, obtaining sensitivity values of 1 × 105 cell/ml by photoluminescence and 1 × 102 cell/ml by bioimpedance. This methodology represents a useful bioanalytical approach for the determination of Staphy...

Attenuated total reflectance-Fourier transform infrared (ATR–FTIR) spectroscopy and multivariate analysis were used to study honey intentionally adulterated with standard sugar solutions (glucose, fructose and sucrose), and also with cheap syrups (corn, inverted and cane sugar). By using the principal component analysis (PCA) method on pure and adulterated (0–100%) honey samples, the determination of the type of adulterant was realized in an easy way through the use of the two- and three-dimensional PCA score plots. From this analysis, a tetrahedral structure was obtained. Superior vertex is formed by the set of samples of pure honey, whereas the edges are formed by the adulterant sugars. Partial least squares method was employed to develop optimal calibrations for the six adulterants used, obtaining values of standard error of calibration in the range 0.377–0.583 and standard error of prediction in the range of 1.550–3.150 for the standard sugars, which suggest a good predictive capacity of the model emp...

We performed a Raman scattering study of aluminum induced microcrystallization of thin films of phosphorous-doped hydrogenated amorphous silicon (n + a-Si:H). These thin films of heavily doped n + a-Si:H were prepared by plasma enhanced chemical vapor deposition. Afterwards, aluminum was deposited and followed by an annealing process at 523 K in a nitrogen environment during several hours. Raman results reveal the formation of microcrystalline regions distributed in the amorphous matrix, induced by the film annealing in the presence of the aluminum. We have used the spatial correlation model to estimate from the Raman signal the microcrystallite size and its relation with the annealing time. The estimated crystallite size was found to be between 6.8 and 9.5 nm and the broadening and downshift of the signals are explained in terms of the crystallite size and lattice expansion effects due to the annealing process. Conductivity values of the samples as a function of the annealing time are explained in terms of the contributions from the amorphous and from the microcrystalline phases.

Nonlinear optical and electronic properties of nanosized metal particles have drawn considerable attention because of their strong and size-dependent plasmon resonance absorption. In a metal nanoparticle system such as gold dispersed in a transparent matrix, an absorption peak due to surface plasmon resonance is usually observed in the visible spectral region. Metal nanoparticles are of special interest as nonlinear materials for optical switching and computing because of their relatively large third-order nonlinearity (χ3) and ultrafast response time. The purpose of this study was to analyze the nonlinear optical properties of biosynthesized gold nanoparticles. The samples were prepared by biosynthesis method using yeast extract as reducing agent and the nonlinear optical properties of the nanoparticles were investigated using a single beam Z-scan technique with a beam power of 20 mW and operated at wavelength of 514 nm. The reaction between metal ions and yeast extracts were monitored by UV–visible spectra of Au nanoparticles in aqueous solution with different pH (3-6). The surface plasmon peak position was shifted from 528 nm to 573 nm, according to of pH variation 4 to 6. The average particle size was calculated by the absorption peak position using the Fernig method, from 42 to 103 nm. The z-scan curves showed a negative nonlocal nonlinear refractive index with a magnitude dependent on the nanoparticle size.

We have analyzed the titration process of gold nanoparticles with several amounts of protein A (0.3, 0.5, 1, 3, 6, and 9lg/ml) in the presence of NaCl, which induces aggregation if the surface of particles is not fully covered with protein A. The colloidal solutions with different particle size (16, 18, 20, 33 nm) were synthesized by citrate reduction to be conjugated with protein A. UV-Visible spectroscopy was used to mea- sure the absorption of the surface plasmon resonance of gold nanoparticles as a function of the concentration of protein A. Such dependence shows an aggregation region (0 \ x\6 lg/ml), where the amount of protein A was insufficient to cover the surface of particles, obtaining aggregation caused by NaCl. The next part is the stability region (x C 6 lg/ml), where the amount of protein used covers the surface of particles and protects it from the aggregation. In addition to that the ratio between the intensities of both: the aggregates and of the gold nanoparticle bands was plotted as a function of the concentration of protein A. It was determined that 6 lg/ml is a sufficient value of protein A to stabilize the gold nanoparticle-protein A system. This method pro- vides a simple way to stabilize gold nanoparticles obtained by citrate reduction, with protein A.

The self assembled monolayers (SAM) have become in the most popular strategy for design and generate surfaces characterizing by specific functional organic groups. The aimed of this work is applied this SAM as optical transducer in biosensors. The techniques, Infrared (in ATR mode) and UV/Vis spectroscopy have been used to study the films generated in each step in the self assembled process. The SAM was generated as follow; first silane group was added to the glass substrate. After that, the substrates were immersed in a solution containing carbomiide group (EDC). Finally the spiropyran 1',3'-Dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indole] was attached to functionalized slides. In each process absorbance was analyzed by UV/Vis (270 to 500 nm) and FTIR (650 to 1800 cm-1). In UV, the spectra shows an absorbance band centered at 280 associated to EDC film and a lower intensity band centered at 380 nm associated to spiropyran. In FTIR spectra, the Si-Si and Si-O bond are present below the 1250 cm-1. The EDC film shows very weak bands in the region from 1300 to 1800 cm-1. For the spiropyran film the band associated to the C-N, N-O, C=C, C-H and aromatic ring have a very well defined peaks. Once the transducer bands were detected, it was immersed in glucose solution; the infrared spectral show bands are associated to glucose in the transducer.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.