The objective of this research was investigated the effect of polyphenol oxidase microwave treatment on phenolic composition, antioxidant activity and microstructure of loquat fruit. Phenolic profile of methanolic ext...The objective of this research was investigated the effect of polyphenol oxidase microwave treatment on phenolic composition, antioxidant activity and microstructure of loquat fruit. Phenolic profile of methanolic extracts prepared from fresh, and microwave-treated samples were analyzed. Antioxidant activity was also evaluated by 2,2’-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS?+) and 1,1-diphenyl-2-picrylhydrazyl (DPPH+) methods. In addition, polyphenol oxidase inactivation was carried out using a response surface methodology to establish the optimal conditions of treatment. The phenolic content of fresh mesocarp was 311 ± 0.60 mg gallic acid equivalents (GAE)/100g dry weight (DW) and that of microwave-treated mesocarp was 1230 ± 0.36 mg GAE/100g DW. Total phenolic content of water/ methanol extract significantly increases after microwave treatment rather than methanolic extract of fresh loquat. Five glycoside phenolics were identified by HPLC-DAD-MS as 3-caffeoylquinic acid, 3-p-coumaroylquinic acid, 5-caffeoylquinic acid and quercetin-3-O-sambubioside. Methanolic extract of microwave-treated mesocarp showed higher antioxidant activity than that of fresh mesocarp. Thus, polyphenol oxidase inactivation by microwave energy preserved the integrity of phenolic compounds as well as antioxidant activity in mesocarp extracts prepared from loquat fruit. It was also noted that phenolics were more abundant in the microwaved samples than in the fresh samples.展开更多
We report the synthesis of undoped ZnO and Al-doped ZnO (ZnO:Al) nanowires grown using a two-step process: (a) preparation of the seed layer, and (b) growth of the nanostructures. In the first step,? 10 mM solutions o...We report the synthesis of undoped ZnO and Al-doped ZnO (ZnO:Al) nanowires grown using a two-step process: (a) preparation of the seed layer, and (b) growth of the nanostructures. In the first step,? 10 mM solutions of zinc acetate dihydrate and 1-propanol were spin coated on polyethylene terephthalate? (PET) substrate at 2000 rpm by 30 s. Vertical nanowires were then grown by dipping the substrates in an equimolar solution of zinc nitrate hexahydrate and hexamethylenetetramine. As doping source, aluminum nitrate nonahydrate powders were added in the solution. In the solutions, Al doping concentrations were established as 0.5 At %, 1.0 At %, 2.0 At % and 3.0 At %, respectively. The hydrothermal process were carried out with a commercially microwave at 140 W power setting. The nanowires were characterized optically and morphologically. XRD patterns show the presence of ZnO, Zn(OH)2 and Zn6Al2O9. Scanning electron microscopy analysis showed that the size of ZnO nanowires was 50 nm in diameter. The undoped ZnO and ZnO:Al nanowires bandgap energy was obtained from optical transmission spectra.展开更多
In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has variou...In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has various industrial applications such as tapping, drilling, dry machining and punching. Angular silicon carbide (SiC) was used as an abrasive particle with a grain size of 350-450 μm. Erosion tests were carried out using different incident angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s, an abrasive flow rate of 0.7 ± 0.5 g/min, and the test temperature was between 35°C and 40°C. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were brittle fracture characterized by radial cracks on the surface by multiple impact and a few pits at 30°, while a few cracks and the formation of craters in random positions were observed at angles near or at 90°. Elliptical scars were observed at 30° and 45°, which are a characteristic feature when the specimens are impacted at low-incident angles (α ≤ 45°) whereas a roughly circular scar was seen at 60° and 90°. In addition, roughness variations were analyzed using atomic force microscopy (AFM), before and after the erosion tests, and the results exhibited an increase in the roughness as the TiN samples were impacted at angles near or at 90°.展开更多
文摘The objective of this research was investigated the effect of polyphenol oxidase microwave treatment on phenolic composition, antioxidant activity and microstructure of loquat fruit. Phenolic profile of methanolic extracts prepared from fresh, and microwave-treated samples were analyzed. Antioxidant activity was also evaluated by 2,2’-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS?+) and 1,1-diphenyl-2-picrylhydrazyl (DPPH+) methods. In addition, polyphenol oxidase inactivation was carried out using a response surface methodology to establish the optimal conditions of treatment. The phenolic content of fresh mesocarp was 311 ± 0.60 mg gallic acid equivalents (GAE)/100g dry weight (DW) and that of microwave-treated mesocarp was 1230 ± 0.36 mg GAE/100g DW. Total phenolic content of water/ methanol extract significantly increases after microwave treatment rather than methanolic extract of fresh loquat. Five glycoside phenolics were identified by HPLC-DAD-MS as 3-caffeoylquinic acid, 3-p-coumaroylquinic acid, 5-caffeoylquinic acid and quercetin-3-O-sambubioside. Methanolic extract of microwave-treated mesocarp showed higher antioxidant activity than that of fresh mesocarp. Thus, polyphenol oxidase inactivation by microwave energy preserved the integrity of phenolic compounds as well as antioxidant activity in mesocarp extracts prepared from loquat fruit. It was also noted that phenolics were more abundant in the microwaved samples than in the fresh samples.
文摘We report the synthesis of undoped ZnO and Al-doped ZnO (ZnO:Al) nanowires grown using a two-step process: (a) preparation of the seed layer, and (b) growth of the nanostructures. In the first step,? 10 mM solutions of zinc acetate dihydrate and 1-propanol were spin coated on polyethylene terephthalate? (PET) substrate at 2000 rpm by 30 s. Vertical nanowires were then grown by dipping the substrates in an equimolar solution of zinc nitrate hexahydrate and hexamethylenetetramine. As doping source, aluminum nitrate nonahydrate powders were added in the solution. In the solutions, Al doping concentrations were established as 0.5 At %, 1.0 At %, 2.0 At % and 3.0 At %, respectively. The hydrothermal process were carried out with a commercially microwave at 140 W power setting. The nanowires were characterized optically and morphologically. XRD patterns show the presence of ZnO, Zn(OH)2 and Zn6Al2O9. Scanning electron microscopy analysis showed that the size of ZnO nanowires was 50 nm in diameter. The undoped ZnO and ZnO:Al nanowires bandgap energy was obtained from optical transmission spectra.
文摘In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has various industrial applications such as tapping, drilling, dry machining and punching. Angular silicon carbide (SiC) was used as an abrasive particle with a grain size of 350-450 μm. Erosion tests were carried out using different incident angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s, an abrasive flow rate of 0.7 ± 0.5 g/min, and the test temperature was between 35°C and 40°C. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were brittle fracture characterized by radial cracks on the surface by multiple impact and a few pits at 30°, while a few cracks and the formation of craters in random positions were observed at angles near or at 90°. Elliptical scars were observed at 30° and 45°, which are a characteristic feature when the specimens are impacted at low-incident angles (α ≤ 45°) whereas a roughly circular scar was seen at 60° and 90°. In addition, roughness variations were analyzed using atomic force microscopy (AFM), before and after the erosion tests, and the results exhibited an increase in the roughness as the TiN samples were impacted at angles near or at 90°.
