Effect of Vacuum Impregnation-Dehydration on the Mechanical Properties of Apples

The effect of sucrose solution concentration and vacuum/atmospheric pressure periods on the mechanical properties of apples (Gala var.) was studied through a stress relaxation test. The empiric model proposed by Peleg was used to fit the curves and the parameters a (level of relaxation) and b (relaxation rate) were evaluated. The experimental results obtained in this study showed that vacuum impregnation conditions had a great influence on the final mechanical properties of the apples. The Peleg model fitted well the data from the stress relaxation curves and may be useful for assessing sample deformation resulting from the vacuum impregnation process.     

Efficient Solvent-Free Synthesis of Sucrose Esters via Sand-Milling Pretreatment on Solid–Liquid Mixtures

A general and efficient method, involving sand-milling pretreatment and base-catalyzed transesterification of sucrose and fatty acid methyl ester (FAME), was presented for the solvent-free synthesis of sucrose esters. A metastable homogeneous paste with a solid particle size of 13 μm (D₅₀) was obtained by milling at 1000 rpm for 1 h. This reaction mixture generated a total SE yield of 88.2% with a methyl stearate (MS) conversion of 91.4% using K₂CO₃ as a catalyst at 135 °C for 3 h at a stirring rate of 500 rpm, while those without milling (D₅₀, 153 μm) yielded a total sucrose fatty acid esters (SE) of 49.3% with a MS conversion of 83.1% under the same reaction conditions. The reaction kinetics revealed that the reaction mixture with milling pretreatment displays a shorter induction time and a faster reaction rate for the formation of SE. The promotion of the solvent-free synthesis of SE in the current study could be attributed to the reduction of solid particle sizes and the increased compatibility of solid–liquid phases. We believe that this strategy could be used as a general way for strengthening other heterogeneous reactions in the organic synthesis.     

Effect of sucrose on rheological properties of aqueous zirconia suspensions with polyacrylate

The role of pH, additive concentration, aging time and solids loading in determining the rheological properties of aqueous zirconia suspensions, which contained polyelectrolyte and sucrose molecules, was investigated. It was found that at alkaline pH, the appropriate sucrose addition (4 wt.%) enhanced the stability of zirconia suspensions with polyacrylate, and the amount of polymer required to obtain the maximum fluidity decreased as sucrose was added. However, the positive effect of sucrose on stability cannot maintain at the higher solids loading (40 vol.%) because of the bridging attraction between the overlapping adlayers. On the other hand, the effectiveness of sucrose would be greatly weakened by hydrolyzation in acidic media as well as biodegradation with aging time.     

SECONDARY NUCLEATION OF SUCROSE BY FLUID SHEAR IN AQUEOUS SOLUTIONS

The motivation for this work was based on two hypotheses: subcritical nuclei of sucrose may be generated by secondary nucleation using a fluid shear field acting on the surface of a growing seed crystal in aqueous solutions, and a near-dynamic equilibrium distribution of embryos may be attained. These were supported experimentally. The value of a σ-based model parameter, a, was obtained by describing the system by a Boltzman- like distribution model. The number concentration of subcritical nuclei was well described by the model. Despite differences in experimental method and in the basic nature of the solute, sucrose, the behavior of the system and results were similar to those obtained in the earlier work using aqueous salt solutions [Sung et al. (1973), Jagannathan et al. (1980)].     

蔗糖酶促水解制取富果糖浆新工艺

提出了将蔗糖酶促水解与产物分离同步进行制备富果糖桨的新方法。在装填Ｃａ［２＋］型离子交换树脂的反应－分离柱内考察了各种操作条件对蔗糖转化率和果葡糖分离度的影响。     

Enhanced photocatalytic water splitting activity of carbon-modified TiO2 composite materials synthesized by a green synthetic approach

We report a green and facile approach for the preparation of carbon-modified (C-modified) TiO₂ composite materials by hydrothermal synthesis followed by pyrolytic treatment. The resultant materials were characterized by powder X-ray diffraction (XRD), nitrogen physisorption studies, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). The photocatalytic performances of these materials were evaluated by calculating the amount of hydrogen evolved from the decomposition of water under solar simulated irradiation conditions. An improvement was achieved from no H₂ evolution at all with the bare TiO₂, to an evolution of 0.21 mL g⁻¹ h⁻¹ from a composite material modified with an optimum carbon loading of 3.62%. These results suggested that the interaction of carbon with predominantly rutile form of TiO₂ can promote shallow trapping of photogenerated electrons in the oxygen vacancies. This phenomenon consequently enhances the photocatalytic activity by minimizing charge carrier recombination, a characteristic demonstrated by fluorescence quenching of the TiO₂ emission.     

Fast simultaneous analysis of caffeine, trigonelline, nicotinic acid and sucrose in coffee by liquid chromatography–mass spectrometry

A rapid liquid chromatography–mass spectrometry method for the simultaneous quantification of caffeine, trigonelline, nicotinic acid and sucrose in coffee was developed and validated. The method involved extraction with hot water, clarification with basic lead acetate and membrane filtration, followed by chromatographic separation using a Spherisorb^® S5 ODS2, 5 μm chromatographic column and gradient elution with 0.3% aqueous formic acid/methanol at a flow rate of 0.2 mL/min. The electrospray ionization source was operated in the negative mode to generate sucrose ions and in the positive mode to generate caffeine, trigonelline and nicotinic acid ions. Ionization suppression of all analytes was found due to matrix effect. Calibrations curves prepared in green and roasted coffee extracts were linear with r² > 0.999. Roasted coffee was spiked and recoveries ranged from 93.0% to 105.1% for caffeine, from 85.2% to 116.2% for trigonelline, from 89.6% to 113.5% for nicotinic acid and from 94.1% to 109.7% for sucrose. Good repeatibilities (RSD < 5%) were found for all analytes in the matrix. The limit of detection (LOD), calculated on the basis of signal-to-noise ratios of 3:1, was 11.9, 36.4, 18.5 and 5.0 ng/mL for caffeine, trigonelline, nicotinic acid and sucrose, respectively. Analysis of 11 coffee samples (regular or decaffeinated green, ground roasted and instant) gave results in agreement with the literature. The method showed to be suitable for different types of coffee available in the market thus appearing as a fast and reliable alternative method to be used for routine coffee analysis.     

ANALYSIS OF RETENTION AND FLUX DECLINE DURING ULTRAFILTRATION OF LIMED SUGARCANE (CLARIFIED) JUICE

The flux decline behaviour of sugarcane juice solution during ultrafiltration (UF) process was studied both experimentally and theoretically. Rate of flux decline was analyzed under varying operating conditions such as pressure (550, 690, and 830kPa) and feed concentration (11, 14, 17, 20 brix). A solution of the clarified limed sugarcane juice containing low molecular weight (LMW)solutes, mainty sucrose, and high molecular weight solutes (HMW) like proteins, fats and wax, etc., was subjected to UF in a stirred cell employing a cellulosic membrane (Spectra Por). Under typical experimental conditions, solution flux was found to reach a steady state value in about three hours. High molecular weight solutes (e.g., proteins)retained by the membrane formed a gel like porous layer on top of the membrane surface. Relatively lighter molecular weight solutes (e.g., sucrose)were mostly permeable, though also partly retained within the gel layer. A mathematical model was developed to describe the flux decline behaviour during UF of sugarcane juice. The model analysis takes into account the formation of polarized concentration boundary layers of both types of solutes, permeable as well as non-permeable. Decline in the flux of sugarcane juice was attributed to the combined effects of gel layer formation as per the cake filtration theory and the development of osmotic pressure of sucrose in boundary layer; although contribution of osmotic pressure exerted by sucrose in flux decline was found to exist only during initial stage of filtration. The model predictions were found to agree well with the experimental data.