RESUMO
Strawberries are highly consumed around the world; however, the post-harvest shelf life is a market challenge to mitigate. It is necessary to guarantee the taste, color, and nutritional value of the fruit for a prolonged period of time. In this work, a nanocoating based on chitosan and ZnO nanoparticles for the preservation of strawberries was developed and examined. The chitosan was obtained from residual shrimp skeletons using the chemical method, and the ZnO nanoparticles were synthesized by the close-spaced sublimation method. X-ray diffraction, scanning electron microscopy, electron dispersion analysis, transmission electron microscopy, and infrared spectroscopy were used to characterize the hybrid coating. The spaghetti-like ZnO nanoparticles presented the typical wurtzite structure, which was uniformly distributed into the chitosan matrix, as observed by the elemental mapping. Measurements of color, texture, pH, titratable acidity, humidity content, and microbiological tests were performed for the strawberries coated with the Chitosan/ZnO hybrid coating, which was uniformly impregnated on the strawberries' surface. After eight days of storage, the fruit maintained a fresh appearance. The microbial load was reduced because of the synergistic effect between chitosan and ZnO nanoparticles. Global results confirm that coated strawberries are suitable for human consumption.
RESUMO
The nonlinear optical response of graphene oxide quantum dots (GOQDs) fabricated by the carbonization and exfoliation of electrospun polyacrylonitrile (PAN) fibers is reported. Electrospun and carbonized fibers were characterized by SEM and XPS. SEM micrograph confirmed the formation of PAN fibers of 153.44 ± 6.44 nm, while by XPS the binding energies associated with sp2 and sp3 carbon hybridizations were found, after the carbonization process. On the other hand, the GOQDs obtained were characterized by photoluminescence (PL), UV-Vis, Raman spectroscopy, and High-Resolution Transmission Electron Microscopy (HRTEM). The GOQDs size of 10 nm was estimated by HRTEM. Raman spectroscopy showed the D and G bands associated with the sp2 and sp3 hybridizations of the GOQDs, by PL two energy values of 2.67 and 2.97 eV were calculated. The UV-Vis spectrum showed two absorption bands confirming the presence of GOQDs. The nonlinear characterization was carried out using the P-scan technique, previously photodepositing GOQDs onto an optical fiber, using a coherent radiation source at a wavelength of 1550 nm. The results obtained showed a saturable absorption behavior with a value of ß = - 2.474 × 10 - 4 m / W and a nonlinear susceptibility of χ ( 3 ) ≈ - 7.749 × 10 - 4 ( e s u ) . The results of this work showed that GOQDs obtained can be used for optical switching applications.
RESUMO
OBJECTIVE: To determine the concentration of lead (Pb), cadmium (Cd), and chromium (Cr) and establish the possible association of these heavy metals with some sociodemographic factors. MATERIAL AND METHODS: A representative sample of one hundred dental students from the National Autonomous University of Mexico living in Mexico City participated in this study. Unstimulated human whole saliva samples were analyzed by Atomic Absorption Spectroscopy. RESULTS: Concentrations of Pb, Cd, and Cr were higher than those reported elsewhere: Pb (X = 3.10 micrograms/dL-1; Maximum: 16.8 micrograms/dL-1 and Minimum: 0.04 microgram/dL-1), Cd (X = 0.25 microgram/dL-1; Maximum: 2.04 micrograms/dL-1 and Minimum: 0.004 microgram/dL-1) and Cr (X = 1.43 micrograms/dL-1; Maximum: 4.82 micrograms/dL-1 and Minimum: 0.05 microgram/dL-1). No association was found between the variables studied (age, sex, geographic area and canned food consumption) with Pb and Cr. However, an inverse association was found between Cd and age (Chi 2 = 5.9012, p < or = 0.05); (gamma = -0.5224, p < or = 0.05). CONCLUSIONS: Salivary monitoring can be used for detection of environmental pollutants (atmospheric or occupational), in addition for detection of drugs, and local and systemic diseases. Heavy metal pollution continues to be a public health problem, and therefore the government should form a program for eliminating pollutants from the environment. Likewise, other studies should be carried out to verify the association between variables such as sex, age, use of glazed ceramics, nutrition, and home address with the concentrations of heavy metals in saliva.