Diffusion of sodium chloride in green olives

The diffusivity of sodium chloride in green olives was investigated in laboratory experiments. The olives were immersed in brines of limited volume and salt absorption was measured from changes in brine concentration. The salt diffusivity was determined by a numerical method of non-linear regression analysis. Low salt diffusivity values, ranging from 3·2 × 10⁻¹¹ to 4·3 × 10⁻¹¹ m² s⁻¹, with a mean value of 3·8 × 10⁻¹¹ m² s⁻¹, were obtained, due to the high resistance to mass transfer of the olive skin and flesh. Pretreatment of the olives in 1·8% sodium hydroxide solution, used to remove the bitter component oleuropein, has the added advantage of increasing the salt diffusivity almost 5-fold.     

Variations in Dextrose Equivalent and Dynamic Rheology of Dextrin Obtained by Enzymatic Hydrolysis of Edible Canna Starch

We aimed to evaluate the dextrose equivalent and the dynamic rheological parameters of dextrin obtained by hydrolysis of edible canna starch by using α-amylase enzyme. We found that the dextrose equivalent value and dynamic rheological properties, as presented by storage and loss modulus (G? and G″) values, varied with the incubation time (1, 3, and 5 h) and α-amylase concentration (0.03, 0.04, 0.05, and 0.06% w/w). Increase in the incubation time and α-amylase concentration increased the dextrose equivalent from 9.0 ± 0.2 to 21.3 ± 1.9 and decreased the storage modulus (G′) from 3747.4 to 18.0 Pa and the loss modulus (G″) from 659.4 to 5.5 Pa at 25°C. Meanwhile, G′ decreased from 27781.0 Pa to 11313.1 Pa and G″ decreased from 6647.2 Pa to 1826.4 Pa at 95°C.     

Modelling water diffusion during long-grain rice soaking

Three different mathematical equations were obtained by solving the diffusion equation of Fick analytically for an infinite cylinder with three different boundary conditions: (i) immediate surface saturation; (ii) surface resistance; (iii) two layers with different diffusion properties. The soaking of long-grain white rice (La Belle) can best be approximated by a model where an immediate surface saturation is assumed, while the two-layer model gives the best approximation in simulating the moisture uptake of brown rice. The activation energies of the diffusivity through the endosperm and the testa were calculated, assuming an Arrhenius type equation for diffusion dependence on temperature, to be 22·5 kJ mol⁻¹ and 64·5 kJ mol⁻¹.     

Finite Element Analysis of Nonlinear Water Diffusion During Rice Soaking

The formulation of a finite element model is described that could be used to analyze water diffusion during rice soaking with concentration dependent diffusivity and change in the size of rice. The rice is divided into 135 elements and moisture distribution with time is calculated. Knowing the moisture absorbed by each element, the nodal displacements are obtained by minimizing the potential energy of the system. Average mass diffusivity of milled rice decreased from 6.4 × 10⁻⁷ to 3.0 × 10⁻⁷ m²/hr as the moisture content increased from 13 to 50%. The density and concentration dependent mass diffusivity model adequately described experimental data.     

Drying behaviour of hazelnuts

A diffusion-based drying model has been used to model the single-layer drying of whole hazelnuts (hull, air-gap and kernel). The drying of whole hazelnut was simulated by means of the numerical solution of Fick's second law for a composite solid consisting of an air gap which is between two solid bodies. The Crank–Nicholson implicit numerical method has been applied to solve the diffusion equation with variable mass diffusivity for whole hazelnut. The numerical data so obtained has been presented in the form of a series of curves which represent the drying characteristics of a whole hazelnut. Experimental results from whole hazelnuts were correlated with the theoretical results. A correlation describing the diffusivity of the whole hazelnut with moisture content and temperature was established, when the expression of diffusivity for hazelnut was used. Predicting the drying behaviour of the hazelnut for a known value of initial moisture content, equilibrium moisture and equivalent radius, a good agreement was obtaind between the experimental data and prediction. Whole hazelnut diffusivity was determined at 25–45°C, air velocity 0·2–0·3 ms⁻¹, 60% relative humidity of air, using the theoretical curves that best fit the data. The diffusivity of whole hazelnut was determined as a function of drying air temperature and velocity. © 1998 SCI.     

Enhancement of glucose production from maltodextrin hydrolysis by optimisation of saccharification process using mixed enzymes involving novel pullulanase

Pullulanase is important to enhance the production and quality of glucose from starch hydrolysis by mixed enzymatic saccharification. To improve glucose production, it would be necessary to manipulate the enzymatic saccharification process and conditions. For enzymatic saccharification involving the newly identified recombinant pullulanase, glucose, maltose and isomaltose were detected, and glucose was the main product from maltodextrin hydrolysis, with the dextrose equivalent value over 99.5%. During the saccharification process, there would be a balance between glucose and disaccharides due to enzymatic hydrolysis and its reverse reaction. With the optimised ratio of glucoamylase to pullulanase (50:1) and dry maltodextrin concentration (20%, w/w), the glucose content (DX) around 99% was obtained with the space‐time yield of 6 mg g^?1·h. After optimisation by orthogonal design and response surface methodology, the DX value of 99.35% was achieved with enzyme loading 75 U g^?1 at 55 °C and pH 4.5 for 36 h.     

Preparation of maltotriose by hydrolyzing of pullulan with pullulanase

In this paper, maltotriose was prepared by hydrolyzing of pullulan with pullulanase. The optimal hydrolyzing conditions were investigated and the optimum conditions were as follows: time 6 h; pH 5.0; temperature 45 °C; amount of pullulanase, 10 ASPU/g; concentration of pullulan, 3% (w/v). Under these conditions, the dextrose equivalent value reached up to 30.1. The hydrolysate was filtrated through a filter membrane that could intercept any particle whose molecular weight was more than 1,000 Da, concentrated to 20% (w/v) and precipitated with 8 volumes of ethanol. The product of maltotriose was obtained by drying the precipitate at 80 °C for 2 h. The content of maltotriose in the product and the yield of maltotriose were 93.5% (w/w) and 87.3% (w/w), respectively. Results of experiments indicated that this was a promising way of preparation of maltotriose.     

Thermal conductivity of tomato paste

Experimental measurements of the thermal conductivity and thermal diffusivity of tomato paste at concentrations of 27–44° Brix are reported. The thermal conductivity was measured in a guarded hot-plate apparatus while the diffusivity was estimated by a simplified transient method. The thermal conductivity (λ) values fell in the region of 0·460–0·660 W m^?1 K^?1, decreasing with increasing solids concentration and increasing as the temperature was raised from 30 to 50°C. The temperature effect was less pronounced at higher solids concentration. The thermal diffusivity of tomato paste at 35° Brix and 20°C was estimated as 1·42 × 10^?7 m² s^?1, which is in good agreement with data from the steady-state method.     

柠檬黄素在淀粉凝胶内的扩散特性研究

测定了在4℃和35℃条件下柠檬黄素在3种浓度的小麦﹑小米淀粉凝胶内的扩散系数。结果表明,在相同条件下,与小麦淀粉凝胶相比,柠檬黄在小米淀粉凝胶内的扩散较慢。扩散系数随着凝胶浓度的减小而增大,随着温度升高而升高。与改变浓度相比,降低温度更能有效地降低柠檬黄在淀粉凝胶内的扩散速度。     

Modeling of Salt Diffusion in White Cheese during Long-Term Brining

Salt transport in white cheese was investigated at two brine concentrations (15 and 20% w/w) and at three temperatures (4, 12.5 and 20°C) for each brine concentration. Two mathematical models were developed based on treating the cheese samples as finite or semi-infinite bodies. Theoretical and experimental salt concentration profiles were in good agreement. The semi-infinite model was valid only for low Fourier numbers, i.e., Fo≤0.07. Effect of convectional flow was insignificant. Salf diffusivity remained constant with time, and an Arrhenius-type equation described its variation with temperature. Salt diffusivity in white cheese was estimated as 0.21 × 10^?9 m²/sec at 4°C and 0.31 × 10^?9 m²/sec at 12.5°C for both brine concentrations and as 0.39 × 10^?9 m²/sec for brine concentration 15% (w/w) and 0.34 × 10^?9 m²/sec at 20°C for 20% (w/w).     

An Improvement of the Cell Diffusion Method for the Rapid Determination of Diffusion Constants in Gels or Foods

A diffusion cell was designed to study the apparent diffusion coefficient of solutes through foodstuffs. The mathematical model corresponding to the experimental setup did not assume quasi-steady state diffusion within the slice of food. It was used to obtain the effective diffusion coefficient of NaCl through 3% Agar gels. The results were compared to those obtained by using two agar gel cylinders at different concentrations. The diffusion coefficient of Cl^? in gel at 25°C was obtained with at least the same precision (D = 1.30 × 10^?9 m²/sec, S_D= 0.03 × 10^?9 m²/sec) within less than 110 min compared to a few hours with the two cylinder technique. With the mathematical model used to determine diffusion coefficients, the equilibrium ratio between solute concentration in solution and at the interface of foodstuff can be determined.     

Studies on the purification of banana polyphenoloxidase

Studies on the extractability of polyphenoloxidase (PPO) from the pulp of five banana cultivars revealed a varietal difference in the nature of binding of the PPO in the cell, with the enzyme being entirely in the soluble fraction in one and partly associated with the cell wall in others, necessitating use of a detergent to release it from the latter. Partial purification by acetone precipitation and chromatography using a DEAE-cellulose column yielded two major fractions DE-I and DE-II with purifications of 4- and 16·3-fold and activity recoveries of 38·2 and 43·3% respectively. Further gel filtration of the two fractions on a Sephadex G-100 column improved the purifications to 44- and 50-fold respectively with full activity recovery. Polyacrylamide gel electrophoretic studies showed the two fractions to be composed of isoenzymes differing in pattern. The purified enzyme showed maximum absorption at 275 nm.     

Ascorbic acid in food: Development of a rapid analysis technique and application to diffusivity determination

A rapid, easy to handle and low cost assay of ascorbic acid was developed, which consists in miniaturization on microplate of a redox reaction monitored spectrophotometrically, the signal being directly related to the concentration of ascorbic acid in the sample. This method was investigated in accordance with the prerogative of regulation covering food additives in terms of linear range/linearity, limits of detection and quantification, accuracy (including trueness and precision), robustness and selectivity. The application of the method was tested to determine ascorbic acid diffusivity in agar gel used as an aqueous food simulant. The diffusivity value obtained was 0.31 × 10^?9 m² s^?1, with a confidence interval of 20% at 95% level. Accuracy of the assay and of the point’s location on ascorbic acid profiles were examined by Monte-Carlo method to assess their influence on accuracy of diffusivity value obtained. Assay uncertainty was clearly demonstrated to be a critical parameter.     

Diffusion coefficients of humic substances in agarose gel and in water

Measurements of the diffusion coefficients of five different humic substances (HS) have been performed in water and in agarose hydrogels at several pH values (in the range of 3-10) and gel concentrations (in the range of 0.7-3% w/w). Fluorescence correlation spectroscopy (FCS) and classical diffusion cells were used in parallel to probe diffusion over both microscopic and mesoscopic distance scales. In general, agreement between the techniques was reasonable, which indicated that local nonhomogenities in the gel did not play an important role. Diffusion coefficients (D) in the gel were generally in the range of 0.9-2.5 x 10(-10) m2 s(-1) but were generally only 10-20% lower than in solution. At low pH values, one of the studied humic substances (a peat humic acid, PPHA) formed large aggregates that could not penetrate into the gel and therefore could not be defined by a single D value. The observed decreases of D in the gel for other HS were too large to be explained by the tortuousity and obstructive effects of the gel alone. D decreased slightly with increasing gel concentration and increased slightly with pH. Because modifications of D due to pH were similar in both the gel and the free solution, it is unlikely that complexation with the gel was greatly influenced by the pH. Rather, the main effect that appeared to decrease the diffusive flux in gels was likely small increases in the hydrodynamic radii of the humic macromolecules. An anomalous diffusion model was used to describe the FCS data in the gel. The characteristic exponent determined by fitting the autocorrelation functions with this model decreased only slightly (from 0.96 to 0.90) with increasing gel concentration providing support that HS complexation with the gel fibers was not very important. The results have important implications for our understanding of the fate and behavior of the HS and their associated pollutants and for interpreting metal speciation data obtained using gel-covered analytical sensors.     

Modeling effective diffusivity of volatile organic compounds in activated carbon fiber

Volatile organic compounds (VOCs) comprise 67% of total hazardous air pollutants (HAPs) that are emitted by major industrial point sources into the U.S. atmosphere (1). Adsorption by activated carbon fiber (ACF) has been recognized as one of the feasible regenerative control processes to separate and recover VOCs for reuse. Characteristics of VOCs transport in ACFs are required to efficiently design ACF sorption systems. However, extensive resources are spent experimentally obtaining transient sorption data to design adsorption systems. As an alternative, this work develops a new model that predicts effective diffusivities of VOCs into ACFs. The diffusion process is modeled as Knudsen transport into the ACF open pore spaces coupled with activated surface diffusion on the ACF's internal surface area. Temperature and Darken's factors are included in the surface diffusion model to provide corrections for thermodynamic state and deviation from Fick's Law, respectively. Depth of the adsorption potential well is considered as the product of the heat of adsorption of a reference VOC, an adsorption similarity factor, and a surface diffusion energy factor. Introduction of the adsorption similarity factor in the effective diffusivity model is a new concept providing a means to predict effective diffusivity of similar adsorption systems from a reference system. Experimental data from a short length column are used to determine effective diffusivity of acetone in ACF. Results from this diffusivity model are compared to experimental values for the acetone/ACF system to describe the degree of closure between modeled and experimental results.     

单性木兰枝多酚提取工艺及抗氧化性研究

以单性木兰枝为原材料,采用超声波辅助法对其多酚进行提取,通过响应面试验优化提取工艺条件,并从总抗氧化性、对DPPH·和·OH的清除作用3个方面研究了单性木兰枝多酚的抗氧化活性。结果表明,单性木兰枝多酚的最佳提取条件为丙酮浓度67%,液固比22∶1(mL/g),提取时间20min,该条件下多酚得率为1.45%。单性木兰枝多酚具有一定的总抗氧化活性,但对DPPH·和·OH具有良好的清除能力。     

Sugar Diffusivity in Agar Gel/Milk Bilayer Systems

To study sucrose and lactose transfer between a dairy product and a fruit layer, this system was modeled with milk on the top of a gel containing 1.5% agar, 0.5% citric acid and different concentrations of sucrose (22.8, 43.3 and 61%). Average disaccharide concentrations at different locations were determined for the system after different diffusion times. Experimental data were fitted to a Fickian diffusion model with separate diffusivities in the milk and the agar gel phases, with correlation coefficient r² >0.98. The values of diffusivity estimated were close to those in aqueous solutions containing identical sucrose concentrations.     

Effect of calcium and calmodulin antagonists on ethylene biosynthesis in tomato fruits

The aim of this work was to elucidate the mode of action of calcium in calcium-inhibited ethylene biosynthesis. In one experiment, mature green tomatoes were treated with 1·5% (w/v) CaCl₂+60 μM N-6(aminohexyl)-1-naphthalenesulphonamide (W5). 1·5% (w/v) CaCl₂+60 μM N-6(aminohexyl)-5-chloro-1-naphthalenesulphonamide (W7), 1·5% (w/v) CaCl₂ alone or distilled water (control). The control and the W7 treatment had much higher ethylene production than either the CaCl₂ treatment alone or the CaCl₂+W5 treatment. In another experiment, similar tomatoes were treated with 1·5% (w/v) CaCl₂+15 μM trifluoperazine (TFP). 1·5% (w/v) CaCl₂ only, or distilled water (control). The treatment with 1·5% CaCl₂+15 μM TFP gave higher ethylene production than 1·5% (w/v) CaCl₂ without TFP, and nearly the same level as the control towards the end of the experimental period. For enzyme and intermediate metabolite assays, mature green tomatoes were treated with 1·5% (w/v) CaCl₂ plus either W5 or W7. W5 treatment had a lower ethylene forming enzyme (EFE) activity, higher 1-aminocyclopropane-1-carboxylic acid (ACC) concentration, similar levels of ACC synthase activity and 1-(malonylamino)-cyclopropane-1-carboxylic acid concentration, compared to the control and W7 treatment. As W7 is a more potent calmodulin antagonist than W5, these results suggest a calcium-calmodulin inactivation of EFE activity. © 1998 SCI.     

莴笋渗透脱水有效扩散系数研究

以葡萄糖溶液浓度(10%～40%)和温度(35～65℃)为影响因素,研究了莴笋渗透脱水的动力学过程。分别使用Azuara模型和Fick第二扩散定律计算出了平衡时刻的失水率、固形物增加率以及相应的水分和固形物有效扩散系数。设计了均匀实验,通过曲面拟合的方法得到了水分、固形物有效扩散系数与因素的回归方程。结果表明:失水率随着葡萄糖溶液浓度增加而增大,但随着温度的升高而降低;固形物增加率随着溶液浓度和温度的增加而增加。Azuara模型可用来预测失水率和固形物增加率,通过曲面拟合得到的有效扩散系数回归方程拟合性较高。有效扩散系数反映了失水率和固形物增加率达到平衡时刻的快慢程度。     

Purification and properties of three albumins from Triticum aestivum seeds

Three albumins were isolated from bread wheat seeds by gel filtration on Sephadex G-100 and differential preparative disc-electrophoresis on polyacrylamide gel. The proteins were obtained in sufficient yield and purity to carry out characterisation studies. The electrophoretic mobilities of the three albumins in polyacrylamide discs in glycine—Tris medium, pH 9·5, were 0·28, 0·34 and 0·39 (referred to that of bromophenol blue taken as 1). The isoelectric points were 6·40, 6·40 and 5·35 and the molecular weights 17, 700, 18, 200 and 18, 900, respectively. The amino acid compositions of the purified albumins were very similar. The correlation of the purified albumins with those isolated from bread wheats by other authors is discussed.