Effects of crosslinking degree of poly(vinyl alcohol) hydrogel in aqueous solution: kinetics and mechanism of copper(II) adsorption

Recently, a renewed interest in hydrogels for heavy metal removal of wastewater has been growing because of embarking opportunities in industrial applications. One of the most interesting hydrogels potentially used as absorbent is poly(vinyl alcohol) (PVA), owing to its biocompatibility. In this study, the adsorption capacity of copper(II) ion onto PVA hydrogel (PVAH) adsorbents with different crosslinking degrees of 1, 3 and 5 % from aqueous solution was investigated. The PVAH adsorbents were prepared from PVA, using glutaraldehyde as a crosslinking agent. Their properties were determined by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and water absorption measurement. The results showed that PVA was crosslinked with glutaraldehyde. It exhibited an equilibrium swelling ratio in the range of 195–250 %, depending on the crosslinking degree with different PVAH structures defined from SEM micrographs. The adsorption capacity of copper(II) ion onto PVAH adsorbents was investigated and found that higher crosslinking degree decreased the absorption capacity. This behavior is due to the decrease in reactive sites, resulting in the decrease of interaction between copper(II) ion and PVA. Besides, the adsorption capacity also depended on contact time, pH and temperature. The adsorption process followed pseudo-second-order kinetic, having a 0.99 correlation coefficient. Intraparticle diffusion was confirmed by the adsorption mechanism controlled by particle and film diffusions.     

Phase Transformation Modelling and Parameter Identification from Dilatometric Investigations

The goal of this paper is to propose a new approach towards the evaluation of dilatometric results, which are often employed to analyse the phase transformation kinetics in steel, especially in terms of continuous cooling transformation (CCT) diagram. A simple task of dilatometry is deriving the start and end temperatures of the phase transformation. It can yield phase transformation kinetics provided that plenty metallographic investigations are performed, whose analysis is complicated especially in case of several coexisting product phases. The new method is based on the numerical solution of a thermomechanical identification problem. It is expected that the phase transformation kinetics can be derived by this approach with less metallographic tasks. The first results are remarkably promising although further investigations are required for the numerical simulations.     

Signaling Pathways Impact on Induction of Corneal Epithelial-like Cells Derived from Human Wharton’s Jelly Mesenchymal Stem Cells

Corneal epithelium, the outmost layer of the cornea, comprises corneal epithelial cells (CECs) that are continuously renewed by limbal epithelial stem cells (LESCs). Loss or dysfunction of LESCs causes limbal stem cell deficiency (LSCD) which results in corneal epithelial integrity loss and visual impairment. To regenerate the ocular surface, transplantation of stem cell-derived CECs is necessary. Human Wharton’s jelly derived mesenchymal stem cells (WJ-MSCs) are a good candidate for cellular therapies in allogeneic transplantation. This study aimed to test the effects of treatments on three signaling pathways involved in CEC differentiation as well as examine the optimal protocol for inducing corneal epithelial differentiation of human WJ-MSCs. All-trans retinoic acid (RA, 5 or 10 µM) inhibited the Wnt signaling pathway via suppressing the translocation of β-catenin from the cytoplasm into the nucleus. SB505124 downregulated the TGF-β signaling pathway via reducing phosphorylation of Smad2. BMP4 did not increase phosphorylation of Smad1/5/8 that is involved in BMP signaling. The combination of RA, SB505124, BMP4, and EGF for the first 3 days of differentiation followed by supplementing hormonal epidermal medium for an additional 6 days could generate corneal epithelial-like cells that expressed a CEC specific marker CK12. This study reveals that WJ-MSCs have the potential to transdifferentiate into CECs which would be beneficial for further applications in LSCD treatment therapy.     

Comparison of Antioxidant Activity of Grape Seed Extract and Fruits Containing High β-Carotene,Vitamin C,and E

Antioxidant activity of a potent antioxidant, grape seed extract, and fruits containing high β-carotene, vitamin C, and vitamin E was measured and compared by 2,2-diphengl-1-picrylhydrazyl radical and ferric reducing antioxidant power assay. The results showed that antioxidant activity of a 20-mg capsule of grape seed extract was approximately 10 to 20 times greater than 1 g of tomato, papaya, banana, and mango. However, if antioxidant activity was calculated per fruit or piece of fruit, the values were comparable. Therefore, consumption of fruit could be a cost-effective way of healthy eating when the price of a dietary supplement is relatively high.     

Effects of roasting degree on radical scavenging activity,phenolics and volatile compounds of Arabica coffee beans (Coffea arabica L. cv. Catimor)

We investigated the effect of roasting degree on volatile and phenolic compounds of coffee beans (Coffea Arabica L. cv. Catimor). The colour, 1,1‐diphenyl‐2‐picrylhydrazyl radical‐scavenging activity and phenolic acids of the aqueous extracts were studied. For the colour, L and b values were increased with an increase in roasting degree. Increasing roasting degrees led to a decrease in radical‐scavenging activity. Maximum radical‐scavenging activity was observed for the light‐roasted coffee. Chlorogenic acid was the most predominant amongst the ten phenolic acids identified, in green and all roasted beans. Syringic acid, p‐coumaric acid, gallic acid and sinapic acid increased with an increase in roasting degree. The volatile compounds were analysed using gas chromatography and mass spectroscopy. Aldehyde was the major volatile compound in green coffee. Our study has demonstrated that light‐roasted coffee gave the most desirable quality of roasted coffee with respect to phenolic content and radical‐scavenging activities.     

Effect of shading on yield, sugar content, phenolic acids and antioxidant property of coffee beans (Coffea Arabica L. cv. Catimor) harvested from north-eastern Thailand

BACKGROUND: Environmental conditions, including shading, generally influence the physical and chemical qualities of coffee beans. The present study assessed the changes in some phenolic compounds, antioxidant activity and agronomic characters of coffee beans (Coffea arabica L. cv. Catimor) as affected by different shading conditions including full sun, three artificial shading conditions using a saran covering (50% shade, 60% shade, and 70% shade) and lychee shade. RESULTS: Bean weight and bean size increased significantly (P < 0.05) when the shade level was progressively increased. The coffee beans grown under lychee shade exhibited superior bean yield, 1000‐bean weight, total phenolic content and antioxidant activity compared to all other beans. Chlorogenic acid was the most predominant phenolic acid in all samples studied, being the highest in the beans grown under lychee shade, followed by 60% shade, 70% shade, 50% shade and full sun, respectively. In contrast, bean grown under full sun had the highest amount of vanillic acid and caffeic acid. CONCLUSIONS: Antioxidant activity was highly positively associated with chlorogenic acid content. The content of total sugar (fructose, glucose and sucrose) was found highest in coffee beans grown in 60% shade, with fructose the predominant sugar. Under climatic conditions similar to this experiment, it is advisable that growers provide shade to the coffee crop to reduce heat from direct sunlight and promote yield as well as obtain good quality coffee beans. Copyright © 2012 Society of Chemical Industry     

Gelatinization and rheological properties of rice starch/xanthan mixtures: Effects of molecular weight of xanthan and different salts

Effects of molecular weight (M_w) of xanthan (XG) and salts (0.1 M NaCl or CaCl₂) on the pasting, thermal, and rheological properties of rice starch (RS) were studied. A series of five XG samples, having various M_w, was prepared by homogenization of native XG solutions in the presence or absence of salts. The presence of salts greatly reduced the intrinsic viscosities, [η], of all XG solutions. Rapid visco-analysis (RVA) data showed that XG addition increased the peak, breakdown, final, and setback viscosities of RS, either in the presence or absence of salts, whereas the pasting temperatures were unaffected. Differential scanning calorimetry (DSC) demonstrated that the gelatinization temperatures of RS were unaffected by XG addition but slightly increased by CaCl₂ addition, whereas the gelatinization enthalpies (ΔH) were significantly decreased by additions of XG and salts. Dynamic shear data revealed weak gel-like behaviour in all paste samples in which their rigidity was decreased by XG addition. Flow tests showed that all pastes exhibited time-dependent shear-thinning (thixotropic) with yield stress behaviour in which the hysteresis loop areas were significantly decreased by XG addition, whereas the other rheological parameters varied differently among the samples, with and without added salt. In general, the effects of XG addition on the pasting and rheological properties of RS were more pronounced with increasing M_w of XG and these effects depended on salts added.