The aim of this work was to study the degree of hydrolysis and changes in the apparent viscosity of casein suspensions as a result of various enzymes addition. Suspensions with 3, 12 and 15 g/100 mL of casein, at pH 5.2, 6.0 and 6.5 were prepared in buffer solutions. Previous standardization; plant (papain and bromelain) and animal (chymosin) enzymes were added to hydrolize the casein suspensions. A control with no enzyme addition was used. The rheological behaviour was determined using a rotational rheometer (Haake RV20), with a cone and plate geometry. The Casson and the power law equations were applied to the data. The degree of hydrolysis was a function of the enzyme, pH and casein concentration, presenting chymosin the highest values. All enzymes showed the highest activity at acidic pH. Also, some substrate inhibition was observed. All samples behaved as non-Newtonian, shear-thinning systems with a yield stress value. In all cases, a significant increase in the viscosity was observed when shifting from 3 to 12 g/100 mL. Further increase in concentration caused an opposite effect. Changes in pH of the casein suspensions affected the viscosity, presenting maximum values at pH 6.0. The Casson equation fitted the results better than the power law model. 相似文献
Ripening is one of the most important processes to occur in fruits and involves changes in colour, flavour and texture. An important goal in quality control of fruits is to substitute traditional sensory testing methods with reliable and quantitative methods. In this study, methyl jasmonate (MJ) (220 μL L?1) and calcium chloride (at 1%) were applied to guava fruits stored at 6 °C. The compression test (CT) and acoustic impact test were used to monitor the shelf life of guavas. The results obtained using both techniques showed that Young’s modulus diminishes as a function of time in all samples; however, the texture of samples treated for 20 days with MJ deteriorated unacceptably, a condition which did not occur in the samples treated with calcium chloride. The control samples had a shelf life of 20 days. In conclusion, it appears that the acoustic impact test is more appropriate than the CT and has the additional advantage of being a nondestructive technique. 相似文献
The electrochemical polymerization of 2-aminobenzene sulfonic acid, also called ortanilic acid (o-ASA), on a gold electrode precoated with polyaniline (PANI), has been carried out. We proved that the electropolymerization of o-ASA is enhanced on PANI electrodes, resulting in thicker films obtained in aqueous media at room temperature. The electrosynthesized film (P(o-ASA)) was characterized by cyclic voltammetry, FTIR and nuclear magnetic resonance. The compensation of P(o-ASA) charge was evaluated using electrochemical quartz crystal microbalance combined with cyclic voltammetry, which showed that the electroneutralization process mainly involves cations. Additionally, copolymers of aniline and o-ASA were electrosynthesized, using a metallic electrode modified with PANI also as a working electrode. The degree of sulfanation of copolymers has been modulated with the proportions of monomers in the electrosynthesis solution. The studies reveal a more important participation of cations in fully sulfonated polyaniline than in partially sulfonated polyaniline. 相似文献
A transient reactor model was used to consolidate and quantify the data of ammonia adsorption microcalorimetry and single ammonia TPD runs, using several members of the commercial CBV series of dealuminated HY zeolites. The model accounts for the competitive re-adsorption of molecules desorbing from multiple sites, using the microcalorimetric data to constrain the desorption energy parameters to physically meaningful values. All TPD profiles were well represented by models consisting of only two or three distinct site types, even though the differential heat plots imply a continuous distribution of sites in the 160-80 kJ/mol range for all catalysts. Increasing dealumination severity is evidenced by a decrease in total site density for sites 100 kJ/mol. While there was no evidence of an enhancement of adsorption strength within the series studied, the range of site strengths available remained the same. There is correspondence between the density of adsites = 100 kJ/mol and the framework Al3+ concentration, although the ratio of these is less than one, even for Si/Al80. The inherent limits in using ammonia adsorption as an acidity probe are briefly mentioned. 相似文献
Chemically deposited SnS thin films possess p-type electrical conductivity. We report a photovoltaic structure: SnO2:F-CdS-SnS-(CuS)-silver print, with Voc > 300 mV and Jsc up to 5 mA/cm2 under 850 W/m2 tungsten halogen illumination. Here, SnO2:F is a commercial spray-CVD (Pilkington TEC-8) coating, and the rest deposited from different chemical baths: CdS (80 nm) at 333 K, SnS (450 nm) and CuS (80 nm) at 293-303 K. The structure may be heated in nitrogen at 573 K, before applying the silver print. The photovoltaic behavior of the structure varies with heating: Voc ≈ 400 mV and Jsc < 1 mA/cm2, when heated at 423 K in air, but Voc decreases and Jsc increases when heated at higher temperatures. These photovoltaic structures have been found to be stable over a period extending over one year by now. The overall cost of materials, simplicity of the deposition process, and possibility of easily varying the parameters to improve the cell characteristics inspire further work. Here we report two different baths for the deposition of SnS thin films of about 500 nm by chemical deposition. There is a considerable difference in the nature of growth, crystalline structure and chemical stability of these films under air-heating at 623-823 K or while heating SnS-CuS layers, evidenced in XRF and grazing incidence angle XRD studies. Heating of SnS-CuS films results in the formation of SnS-CuxSnSy. ‘All-chemically deposited photovoltaic structures’ involving these materials are presented. 相似文献
In this work is report the synthesis by mechanochemical method of a small molecule of the oligophenylene (bisquinoline) design (OBM), excellent optical and electrical properties, and potential use as an electroluminescent material in the form of a nano-film in the manufacture of an organic light-emitting diode (OLED). OBM was synthesized by a Knoevenagel condensation reaction and was chemically characterized by 1H-NMR, 13C-NMR, FT-IR spectroscopy, and AccuTOF-DART mass spectrometry. UV–Vis and fluorescence spectroscopies were used to obtain the optical properties of OBM, both in solution and in film. Also, the OBM film was examined by atomic force microscopy and showed a high degree of homogeneity which allowed the manufacture of an OLED device with ITO/OBM/PEDOT: PSS/Al configuration with a luminance of 2350 cd/m2 when supplied with a fixed current of 15 mA and 10 volts.