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

Recently, chitin and chitosan are widely investigated for food preservation and active packaging applications. Chemical, as well as biological methods, are usually adopted for the production of these biopolymers. In this study, modification to a chemical method of chitin synthesis from shrimp shells has been proposed through the application of high-frequency ultrasound. The impact of sonication time on the deproteinization step of chitin and chitosan preparation was examined. The chemical identities of chitin and chitosan were verified using infrared spectroscopy. The influence of ultrasound on the deacetylation degree, molecular weight and particle size of the biopolymer products was analysed. The microscopic characteristics, crystallinity and the colour characteristics of the as-obtained biopolymers were investigated. Application of ultrasound for the production of biopolymers reduced the protein content as well as the particle size of chitin. Chitosan of high deacetylation degree and medium molecular weight was produced through ultrasound assistance. Finally, the as-derived chitosan was applied for beef preservation. High values of luminosity, chromatid and chrome were noted for the beef samples preserved using chitosan films, which were obtained by employing biopolymer subjected to sonication for 15, 25 and 40 min. Notably; these characteristics were maintained even after ten days of packaging. The molecular weight of these samples are 73.61 KDa, 86.82 KDa and 55.66 KDa, while the deacetylation degree are 80.60%, 92.86% and 94.03%, respectively; in the same order, the particle size of chitosan are 35.70 µm, 25.51 µm and 20.10 µm.

Assuntos

Quitina/química , Quitosana/química , Proteínas/isolamento & purificação , Sonicação , Acetilação , Animais , Peso Molecular , Proteínas/análise , Proteínas/química

RESUMO

Using first principles calculations, we investigate the electronic properties of a new boron nitride based system, the graphene-like boron nitride oxide. We use the Density Functional Theory as implemented in the DMOL3 code, employing the LDA (PWC) and GGA (PBE) for the exchange-correlation term. The atomic sheets are modeled through the (N27B27H17 + (OH)3 + COOH + O) cluster, considering two cases, the OH and carboxylic groups bonded to the nitrogen atom and then bounded to boron atom. Both systems are structurally stable and the gap between the HOMO and LUMO are 1.24 y 2.36 eV, respectively, smaller than the boron nitride sheet (4.84 eV). Moreover, when the carboxylic group is bonded to the nitrogen atom, the system presents high polarity, compared with graphene oxide and with the another configuration.