Chitosan Coatings Modified with Nanostructured ZnO for the Preservation of Strawberries

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.

Recuperation and characterization of calcium carbonate from residual oyster and clamshells and their incorporation into a residential finish

The final disposal of waste generated by human activities has been turned into a great challenge; until now, little attention has been paid to organic waste, particularly from the restaurant sector. This work describes the process of obtaining calcium carbonate contained in oyster and clam shells re-collected in seafood restaurants. The IR absorption spectra of all the samples revealed the presence of characteristic bands of the carbonate group located at 872, 712 and 1414 cm^-1; the peak at 1081 cm^-1 of the clamshells confirms the presence of the aragonite phase. The SEM images allow observing a granular morphology whose agglomerates having a size within the range of 0.5-15 μm in brown shells, and a lower dispersion prevails in the grey species and oyster shells that go from 0.3 to 5.9 μm. All of the shells were found to be composed of carbon (C), oxygen (O₂) and calcium (Ca) in different concentrations. The calcium carbonate obtained from clamshells has an orthorhombic crystalline structure, while the oyster carbonate has a rhombohedral structure as the calcium carbonate used in the construction industry; the morphology particles also coincide with each other. The material obtained combined with a mixture composed of resin, cellulose, and granules were used to prepare a paste, which was used as a residential finish.

Using self-etch adhesive agents with pit and fissure sealants. In vitro analysis of shear bond strength, adhesive remnant index and enamel etching patterns

Purpose

The aim of this study was to evaluate in vitro, the shear bond strength (SBS) and adhesive remnant index (ARI) of pit and fissure sealants (PFS) after enamel conditioning with different new-generation self-etching (SE) agents; additionally, enamel etching patterns were assessed.

Methods

Healthy unerupted third molars surgically removed for therapeutic reasons (n = 25p/g), were randomly assigned to six groups. Conventional etching (CE) or SE was applied prior to pit and fissure sealants bonding. Enamel conditioned surfaces were evaluated by SEM at × 500, × 1000, and × 2000 magnification to determine etching patterns. Subsequently, 25 PFS blocks (3 × 2 × 1.5 mm) p/g were bonded to enamel surface.

Samples were stored in water at 37 °C for 24 h, previous to SBS and ARI test. One-way ANOVA and Tamhane statistic tests were used for SBS; while Mann–Whitney U and Kruskal–Wallis were employed for ARI (p ≤ 0.05).

Results

For SBS test, CE_PFS_3M and SE1_PFS_Shofu groups showed the lowest values (8.74 ± 4.02 and 8.75 ± 3.90, respectively). The highest scores were observed in SE_PFS_Kuraray group (13.46 ± 5.83). Significant differences in SBS and ARI assessments were found. All experimental groups showed type 1 etching pattern.

Conclusion

The etching pattern was less pronounced in self-etching groups, which showed an equal or superior in vitro performance compared to conventional etching agents. The clinical use of self-etching agents could be recommended before pit and fissure sealants application in new dental protocols. The best in vitro performance was observed when both applied materials, self-etching agent and pit and fissure sealant have 10-methacryloyloxydecyl dihydrogen phosphate in their chemical composition.

Ultrasound in the deproteinization process for chitin and chitosan production

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.

Wet chemical synthesis of nanocrystalline hydroxyapatite flakes: effect of pH and sintering temperature on structural and morphological properties

Wet chemical synthesis of hydroxyapatite (HAp) nanostructures was carried out with different solution pH values (9, 10 and 11) and sintering temperatures (300°C, 500°C, 700°C and 900°C). The effects of pH and sintering temperature on the structural and morphological properties of nanocrystalline HAp powders were presented. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were performed to obtain the crystalline structure, chemical composition, morphology and particle size of the HAp powders. The TEM analysis is used in order to observe the rod- and flake-like HAp structures. XRD confirms the presence of both HAp hexagonal and monetite phases, although the monetite phase was less abundant in the resultant powders. Increase in pH reduced the monetite phase and enhanced Ca/P ratio from 1.7 to 1.83. Additionally, an increment in sintering temperature increased the crystallite size from 20 to 56 nm. The SEM analysis revealed the formation of semi-spherical and flake-like HAp structures with preferential flake morphology. An increase in pH and sintering temperature resulted in the growth and coalescence of crystals resulting in a porous capsular morphology. The FTIR analysis confirmed the reduction of carbonate stretching modes with an increase in pH and H-O-H antisymmetric stretching mode is eliminated for powders sintered at 900°C confirming the formation of stable and porous HAp powders.

The effect of cyclic heat treatment on the physicochemical properties of bio hydroxyapatite from bovine bone

This paper focus on physicochemical changes in bio-hydroxyapatite (BIO-HAp) from bovine femur obtained by calcination at high temperatures: 520-620 (each 20 °C) at 7.4 °C/min and from 700 to 1100 °C (each 100 °C) at three heating rates: 7.4, 9.9, and 11.1 °C/min. BIO-HAp samples were obtained using a multi-step process: cleaning, milling, hydrothermal process, calcination in an air atmosphere, and cooling in furnace air. Inductively Couple Plasma (ICP) showed that the presence of Mg, K, S, Ba, Zn, and Na, is not affected by the annealing temperature and heating rate. While Scanning Electron Microscopy (SEM) images showed the continuous growth of the HAp crystals during the calcination process due to the coalescence phenomenon, and the Full Width at the Half Maximum for the X-ray patterns for temperatures up to 700 is affected by the annealing temperature and the heating rate. Through X-ray diffraction, thermal, and calorimetric analysis (TGA-DSC), a partial dehydroxylation of hydroxyapatite was found in samples calcined up to 900 °C for the three heating rates. Also, Ca/P molar ratio decreased for samples calcined up to 900 °C as a result of the dehydroxylation process. NaCaPO₄, CaCO₃, Ca₃(PO₄)₂, MgO, and Ca(H₂PO₄)₂ are some phases identified by X-ray diffraction; some of them are part of the bone and others were formed during the calcination process as a function of annealing temperature and heating rate, as it is the case for MgO.

PbS nanostructured thin films by in situ Cu-doping

PbS:Cu nanocrystalline films were prepared by chemical bath at temperature of 80 degrees C and deposited on glass substrates. Different Cu-doping levels were obtained changing the volume of the Cu-reagent-solution into the PbS growing solution. X-ray diffraction (XRD) and optical absorption (OA) measurements were carried out to characterize the semiconductor. The morphological changes of the layers were analyzed using an atomic force microscopy. Diffraction X-ray spectra displayed peaks at 2 theta = (26.00, 30.07, 43.10, 51.00 and 53.48), indicating growth on the zinc blende face. The grain size determined by X-rays diffraction of the undoped samples, was found -37 nm, whereas with the doped sample was - 32-25 nm. Raman spectra reports strong band in - 133-140 cm(-1) attributed to a combination of longitudinal and transversal acoustic modes. Optical absorption, forbidden band gap energy (E(g)) shift disclose a shift in the range 1.4-2.4 eV. Gibbs free energy calculation for the Cu doping PbS is also included heading.