Role of water state and mobility on the antiplasticization of green and roasted coffee beans

The effect of water on "antiplasticization" and plasticization of green and roasted coffee was studied by textural analysis, sorption isotherms, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). From BET monolayer value to a(w) = 0.61 and 0.75 for green and roasted coffee, respectively, the solid matrix hydration occurred and water induced hardening. Very short NMR T(2) values and the concomitant absence of any DSC endothermic peak assignable to water freezing were observed at these a(w) values. When solid matrix hydration was completed, water started to act as a plasticizing agent, the compressive modulus started to decrease, and NMR revealed the appearance of a new proton pool with increased mobility. According to DSC, only when the plasticizing effect became important did water present enough mobility to freeze. Above this moisture value (a(w) = 0.78 and 0.86 for green and roasted coffee, respectively), water determined a decrease of bean hardness and a further decrease of the elastic modulus.     

线性和非线性方法估计单宁酸共存下形成的无定形铝氧化物上菲的吸附等温线参数比较

采用批实验研究了菲在单宁酸干扰下形成的不同晶形铝氧化物上的吸附现象,并用不同的吸附等温线方程对吸附平衡数据进行了拟合,重点比较了线性和非线性回归方法估计吸附等温线参数的差异。结果表明:菲在各种晶形的铝氧化物上都有明显的吸附,但并不是完全随着单宁酸含量和结晶度的变化而规律性变化。吸附平衡数据以Langmuir、Redlich-Peterson和Dubinin-Radushkevich吸附等温方程,用不同的回归方法估计的等温线参数值均有显著性差异。线性回归得到的参数有不确定性,表明用线性回归来判断吸附等温线能否对吸附平衡数据进行最优拟合是不可靠的。相反,非线性回归能较好地确定菲在不同晶形铝氧化物上的最佳吸附等温线及相应参数。采用R2和χ2共同检验发现,菲在4种不同结晶度(单宁酸与铝的摩尔比(MR)=0,10-3,10-2,10-1)铝氧化物上的最佳吸附等温线方程并不尽相同,分别为Freundlich,Freundlich,Dubinin-Radushkevich和Freundlich,反映了各种晶形的铝氧化物的表面异质性。修正的Freundlich方程比较不同晶形铝氧化物对菲的相对吸附容量顺序为:MR=10-3MR=10-2MR=0MR=10-1。由此,认为菲在无定形铝氧化物上的吸附是熵驱动的结果。     

Sorption behavior of prochloraz in different soils.

The sorption behavior of the imidazole fungicide prochloraz [PCZ; N-propyl-N-[2-(2,4,6-trichlorophenoxy)ethyl]imidazole-1-carboxamide] was studied in batch experiments with different soils. The soil organic matter content was found to control the amount sorbed by different soils. K(d) values ranged from 56 +/- 0 to 552 +/- 10 (mean = 221 +/- 5) and K(OC) values from 7273 +/- 0 to 16250 +/- 1300 (mean = 11829 +/- 303). As calculated from a linear regression of K(d) versus %OC, K(OC) was 12900 +/- 1300. Additionally, the pH value of the soil had considerable influence on the sorption of the weakly basic PCZ (pK(a) = 3.8), giving rise to stronger sorption at lower pH. K(d) values determined on pH-modified soils confirmed the pH dependency. Sorption isotherms on two soils were recorded, initial concentrations ranging from 0.09 to 5.71 mg L(-)(1). The Freundlich isotherm was fitted to the values measured. The Freundlich exponents calculated were significantly smaller than unity, indicating nonlinear sorption. Sorption experiments with two metabolites of PCZ (PCZ-formylurea and PCZ-urea) revealed K(d) values one-fourth to one-third those for PCZ on two soils.     

Action of Oxidants on Water Sorption, 2H Nuclear Magnetic Resonance Mobility,and Glass Transition Behavior of Gluten

Oxidation of vital wheat gluten with potassium bromate and ascorbic acid significantly extends or broadens glassy-rubber transition to a higher final temperature range or moisture content. Thermomechanical and deuterium nuclear magnetic resonance (NMR) data show that the increased stiffness due to oxidation could be detected from the thermomechanical and deuterium NMR mobility level, indicating increased rigid fractions. The oxidation also resulted in increased water sorption, but no significant change in “freezable” water, and a much decreased mobile deuterium NMR signal. Room temperature sorption of water resulted in a glassy-rubbery transition over a ≈10–20% mc range for the control. For the oxidized sample, it started at ≈10%mc, but the transition was gradual and extended into much higher moisture ranges that corresponded to a more rigid fraction of deuterium (NMR) signal. This suggests that the oxidative interactions led to a more rigid gluten fraction, extending the transition to a higher temperature range, perhaps resulting in a more elastic dough.     

Prediction of the water sorption isotherm in air dry soils

Within this work we present a revised pedotransfer function (PTF) that predicts water sorption isotherms for dry soils based on the clay content of the soils. When the water sorption isotherm is plotted as a water retention curve (log water potential plotted against the water content) it typically results in a log linear function as described by Campbell and Shiozawa (1992). The linear function is defined by its slope and a fixed endpoint at zero water content. The reciprocal of the slope shows a strong correlation with the clay fraction. For the calibration of a PTF we measured water sorption data for 18 soils with clay contents from 2% to 61%. The final predictions of the water sorption isotherms from the clay mass fraction were very good if the clay content was higher than 7%. The use of a revised theoretical endpoint at the dry end of the WRC did improve the prediction as compared to the endpoint that has been used in the literature before. In addition Literature data for 22 soils and 3 pure clay minerals were used for validation. The good performance of the PTF only occurred if the clay fraction was dominated by 2:1 clay minerals. The water retention isotherm of soils rich in the 1:1 clay mineral kaolinite could not be predicted by this approach; the actual water content was strongly over-predicted and the water retention curve did not follow a log linear relationship.     

Relationship between meat structure, water mobility, and distribution: a low-field nuclear magnetic resonance study

Nuclear magnetic resonance (NMR) measurements were carried out on pork longissimus muscle, which pre rigor had been manipulated to various muscle lengths, to investigate the relationship between the microstructure of meat and the NMR T(2) relaxation. Distributed exponential analysis of the NMR T(2) relaxation data revealed the existence of three distinct water populations: T(2b), T(21), and T(22). A high, significant correlation was found between the T(21) time constant and the sarcomere length (r = 0.84) and calculated ration of myofilament lattice volume in the I-band and A-band regions, respectively (r = 0.84), considering sigmoid relationships. The result implies that the T(21) time constant mainly is determined by the structure of the myofilament lattice and so strongly supports a previously proposed theory that the T(21) population corresponds to water located within a highly organized myofibrillar protein matrix including actin and myosin filament structures. A high correlation was also found between the T(22) population and the water-holding capacity (WHC) (r = 0.76), which suggests that the WHC is mainly determined by the amount of loosely bound extramyofibrillar water. However, the correlation between NMR T(2) parameters and WHC was further increased (r = 0.84) by including the T(21) time constant in the correlation analysis. This implies that the formation of drip loss is an ongoing process involving the transfer of water from myofibrils to the extracellular space and is affected by structural features at several levels of organization within the muscle tissue. This study demonstrates the advantages of NMR T(2) relaxation as an effective technique for obtaining further understanding of the relationship between the microstructure of meat, its WHC, water mobility, and water distribution.     

Role of water upon the formation of acrylamide in a potato model system

The moisture sorption isotherms of a commercial potato powder were investigated at 20 degrees C for water activities ranging from 0.11 to 0.97. The sorption isotherms were typical type-II sigmoidal curves, with a steep increase in moisture content for water activities above 0.9 and exhibiting hysteresis over the whole water activity range. On the basis of the isotherms, the influence of the initial water activity and moisture content on both Maillard browning and acrylamide formation was determined by heating oil containing potato powder mixtures in a closed stainless-steel tubular reactor. The Maillard browning, as determined spectrophotometrically, showed an optimum at intermediate water activities. The yields of acrylamide, expressed relatively to the molar amount of asparagine, remained constant below 0.8 aw and below moisture contents of about 20% (on a dry basis). For the more intense heat treatments, an increased acrylamide yield was however observed at higher moisture contents, with an optimum at water contents of about 100% (on a dry basis). However, this increase and optimum was not observed at less intense heat treatments. At moisture contents above 100%, a significant decrease in acrylamide yields was assessed, although the water activity increased only marginally in this area of the sorption isotherms. It was thus observed that the acrylamide content was rather dependent upon the moisture content than upon the water activity in the high-moisture potato powder model system.     

Water content or water activity: what rules crispy behavior in bread crust?

A dry crust loses its crispness when water migrates into the crust. It is not clear if it is the amount of water absorbed or the water activity ( a w) that leads to a loss of crispness. The hysteresis effect observed when recording a water sorption isotherm allowed us to study the effects of a w and moisture content separately. All experiments were carried out on model bread crusts made from Soissons bread flour. The effect of water content and water activity on the glass transition of model bread crusts was studied in detail using two complimentary techniques: phase transition analysis (PTA) and nuclear magnetic resonance (NMR). The results were compared with sensory data and results from a puncture test, which provided data on acoustic emission and fracture mechanics during breaking of the crusts. The water content of the crust was found to be decisive for the transition point as measured by PTA and NMR. However, both water content and water activity had an effect on perceived crispness and number of force and sound peaks. From this may be concluded that the distribution of the water in the samples with a history of high water content is more inhomogeneous, which results in crispy and less crispy regions, thus making them overall more crispy than samples with the same water content but higher a w.     

Water uptake mechanism in crispy bread crust

Crispness is an important quality characteristic of dry solid food products such as crispy rolls. Its retention is directly related to the kinetics of water uptake by the crust. In this study, a method for the evaluation of the water sorption kinetics in bread crust is proposed. Two different sorption experiments were used: an oscillatory sorption test and a sorption test in which the air relative humidity (RH) was increased stepwise. These two experiments had different time scales, which made it possible to get a better understanding of the mechanisms involved. Results show that the adsorption and desorption dynamics of the oscillatory sorption test could be described by a single exponential in time. The water uptake rate ( k) was one of the fitting parameters. A maximum in the water uptake rate was found for a RH value between 50 and 70%. The rate parameters of the experiment where RH was increased stepwise were around a factor 10 lower than those derived from oscillatory sorption experiments. This is an important factor when designing experiments for the determination of water uptake rates. In addition, also a parameter describing the time dependence of the rate parameters of the oscillatory sorption experiment was calculated (C), again by fitting a single exponential to the rate parameters. C was in the same range as the rate parameter of the isotherm experiment. This indicates that different (relaxation) processes are acting at the same time in the bread crust during water uptake.     

Glass transition and water effects on sucrose inversion by invertase in a lactose-sucrose system

Enzymatic changes are often detrimental to quality of low-moisture foods. In the present study, effects of glass transition and water on sucrose inversion in a lactose-sucrose food model were investigated. Amorphous samples were produced by freeze-drying lactose-sucrose (2:1)-invertase (20 mg invertase/49.4 g of carbohydrate) dissolved in distilled water. Sorption isotherms were determined gravimetrically at 24 degrees C. Sucrose hydrolysis was determined by monitoring glucose content using a test kit and the amounts of fructose, glucose, and sucrose using HPLC. The glass transition temperatures, T(g), at various water contents were measured using differential scanning calorimetry (DSC). The BET and the GAB sorption models were fitted to experimental data up to a(w) 0.444 and 0.538, respectively. Water sorption and DSC results suggested time-dependent crystallization of sugars at a(w) 0.444 and above. Significant sucrose hydrolysis occurred only above T(g), concomitantly with crystallization. Sucrose hydrolysis and crystallization were not likely in glassy materials.     

Influence of pH and Zinc Concentration on Cadmium Sorption in Acid, Sandy Soils

Batch adsorption experiments were carried out with samples from an A-, Bh- and C-horizon of contaminated sandy soil of podzolic character from the Kempen region at the Dutch-Belgian border. Cadmium sorption was studied on 3 soil samples at 3 different pH-levels (3.6, 4.3 and soil buffered pH) and 3 different additions of zinc (0–40 mg l^-1). Adsorption of cadmium by acid sandy soils can be fitted by a Freundlich adsorption isotherm. Although zinc competes with cadmium for the sorption sites, we observe a two to three times stronger competition effect of the proton cation, which is explained by the chemical properties of both ions. The cadmium adsorption coefficient K_F decreases considerably by an increase of the proton activity used in the sorption experiments. Organic matter content explains for a large part the variation of KF of te three soil samples. Desorption data do not fit the proposed regression model for adssorption. Not all the cadmium, intitially present in the polluted soil, will fylly desorb reversibly. Thus, part of the cadmium may be irreversible bound.     

Sorption of polycyclic aromatic hydrocarbons to mineral surfaces

Minerals contribute crucially to the retention of polycyclic aromatic hydrocarbons (PAHs) in subsurface environments. To investigate the sorption behaviour to mineral surfaces batch sorption experiments were conducted using three PAHs (phenanthrene, pyrene, benzo(a)pyrene) and three mineral sorbents that were representative of subsurface materials (quartz, goethite‐coated quartz, quartz‐montmorillonite mixture). Sorption kinetics showed an instantaneous, considerable PAH sorption to all minerals, except for phenanthrene sorption to quartz at small aqueous‐phase concentrations. Apparent sorption equilibrium was achieved after 4 hours of contact time. The sorption characteristics were fitted to six isotherm models by applying Monte Carlo simulation and nonlinear regression. Best‐fit models were obtained by a model discrimination approach. Phenanthrene and pyrene sorption were best described by the Freundlich isotherm model, with the exception of phenanthrene sorption to quartz (linear isotherm). Good fit results for quartz were also obtained for the combined linear‐Freundlich isotherm. Benzo(a)pyrene sorption to all minerals followed linear high‐affinity isotherms. In the case of phenanthrene and pyrene, the Monte Carlo simulations resulted in mean values with small standard deviations for the isotherm parameters, indicating a negligible influence of the experimental uncertainties on the accuracy of the fitted parameters. For phenanthrene, (i) linear isotherms to quartz and goethite‐coated quartz and (ii) a nonlinear concave‐shaped isotherm to quartz–montmorillonite, assuming a pore‐filling process to micropores formed by clay aggregates, were confirmed. For pyrene, nonlinear convex‐shaped isotherms to the mineral surfaces were assessed. A specific sorption affinity of pyrene to the goethite surface indicated a non‐covalent cation‐π interaction. Small sorption affinities to quartz–montmorillonite support an unfavourable partitioning into the adjacent water.     

Linuron sorption-desorption in field-moist soils

Pesticide sorption or binding to soil is traditionally characterized using batch slurry techniques. The objective of this study was to determine linuron sorption in field-moist or unsaturated soils. Experiments were performed using low-density (i.e., 0.25 g mL(-)(1)) supercritical carbon dioxide to remove linuron from the soil water phase, thus allowing calculation of sorption coefficients (K(d)) at low water contents. Both soil water content and temperature influenced sorption. K(d) values increased with increased water content, if less than saturated. K(d) values decreased with increased temperature. K(d) values for linuron sorption on silty clay and sandy loam soils at 12% water content and 40 degrees C were 3.9 and 7.0 mL g(-)(1), respectively. Isosteric heats of sorption (DeltaH(i)) were -41 and -35 kJ mol(-)(1) for the silty clay and sandy loam soils, respectively. The sorption coefficient obtained using the batch method was comparable (K(f) for sandy loam soil = 7. 9 microg(1)(-)(1/)(n)() mL(1/)(n)() g(-)(1)) to that obtained using the SFE technique. On the basis of these results, pesticide sorption as a function of water content must be known to more accurately predict pesticide transport through soils.     

[A环-U-~(14)C]丙酯草醚在土壤中的吸附与解吸特性研究

丙酯草醚(ZJ0273)是我国拥有自主知识产权的新型高效油菜田除草剂。本文以[A环-U-14C]丙酯草醚为示踪剂,在实验室模拟条件下,采用液体闪烁测量技术对其在7种土壤中的吸附和解吸特性进行了研究。结果表明:(1)丙酯草醚在7种土壤中的吸附等温线均能极显著符合Freundlich、Langmuir和线性模型,相对而言,前两种模型的相关系数R2(0.9883~0.9998)明显高于线性模型(R2=0.9173~0.9593);(2)丙酯草醚在7种土壤中的解吸等温线能被Freundlich模型和线性模型很好地描述;(3)丙酯草醚极易被土壤吸附,不同类型的土壤对其吸附的差异较大,吸附常数KF与土壤有机质含量呈显著正相关,与之对应的解吸率极低。丙酯草醚吸附解吸过程存在明显的滞后现象,应科学合理地在有机质丰富的土壤中使用。     

黄土高原干旱半干旱区生物结皮覆盖土壤水汽吸附与凝结特征

生物结皮是一种广泛分布于干旱半干旱地区土壤表层的特殊复合体,为揭示其对土壤水汽吸附与凝结过程的影响,该研究通过室内定量水汽吸附试验和野外对水汽凝结的连续观测,对黄土高原典型生物结皮(藻结皮、藻藓混生结皮、藓结皮)与裸沙的水汽吸附和凝结特征进行对比研究。结果表明:生物结皮的覆盖显著提升了表层土壤的水汽吸附能力,其平均水汽吸附量比裸沙高66.7%。不同类型生物结皮水汽吸附能力差异显著,表现为藓结皮最高,混生结皮次之,而藻结皮最低。GAB(Guggenheim-Anderson-de Boer)吸附模型能较好的描述生物结皮土壤水汽吸附与解吸附过程,模拟结果决定系数R20.99、均方根误差RMSE0.001 2 g/g及平均相对偏差百分比E16.0%;此外,生物结皮加剧了土壤水汽吸附与解吸附曲线之间的滞后效应,其滞后指数平均是裸沙的2.0～2.9倍。水汽凝结结果显示,水汽凝结过程均受气温与相对湿度等气象因子制约,且生物结皮覆盖下表层土壤的水汽凝结和蒸发过程相较于裸沙更为迅速。同时,生物结皮的日均水汽凝结量是裸沙的1.6～1.8倍。综上,干旱和半干旱地区生物结皮覆盖显著提高了表层土壤的水汽吸附能力、并增加了水汽凝结量,对区域表层土壤的水分运动过程产生了重要影响。     

Multi-level approach for the analysis of water effects in corn flakes

The purpose of this work was to analyze the effect of water on thermal transitions, mechanical properties, and molecular mobility in corn flakes (CF), and their relationships. Commercial common (CCF) and sugar-frosted (SCF) corn flakes were studied in a water content (wc) range from 5 to 20 (% dry basis). The slope of (1)H NMR spin-spin relaxation time T 2* (determined by FID) versus temperature plot changed close to T g. Compression force showed a maximum at wc of ca. 12 and 16% (db) for SCF and CCF, respectively. (1)H NMR complemented DSC data in determining the temperature dependence of water and solid mobility, in order to assess quality of laminated corn products. The results of the present work indicate that while the compression force showed a maximum value as a function of water content, T g values determined by DSC or by spin-spin relaxation decreased progressively with increasing water content.     

Effect of pH on binding of mutagenic heterocyclic amines by the natural biopolymer poly(gamma-glutamic acid)

Poly(gamma-glutamic acid) (gamma-PGA), a nontoxic and biodegradable macropolymer, was evaluated for its efficiency in binding three mutagenic heterocyclic amines (HAs), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-p-2), as affected by pH in a batch mode. The maximum HA sorption was attained for pH 3-7 and decreased sharply for pH less than 3. Binding isotherms obtained at pH 2.5 and 5.5 showed different isotherm shapes that belong to S and L types, respectively. The isotherm data at pH 2.5 were well described by a linear form of the Langmuir equation, while at pH 5.5 it showed two distinct curves, which were precisely fitted as multiple Langmuir curves. The deviation of linearity in Scatchard plot proved the multisite HA sorption. The Brunauer-Emmett-Teller equation also fitted better to isotherm data at pH 5.5, suggesting a multisite sorption caused by multimolecular HA layers on gamma-PGA. High HA sorption levels of 1250, 667, and 1429 mg/g at pH 2.5 and 1429, 909, and 1667 mg/g at pH 5.5 were observed for MeIQ, 4,8-DiMeIQx, and Trp-p-2, respectively. Among the HAs studied, the sorption capacity correlated directly with hydrophobicity of HAs and inversely with the number of methyl groups in HA molecules. The plausible binding mechanism of HAs on gamma-PGA may include a combination of hydrophobic, hydrogen-bonding, ionic, and dipole-dipole interactions.     

Volatile release from aqueous solutions under dynamic headspace dilution conditions.

Static equilibrium was established between the gas phase (headspace) and an unstirred aqueous phase in a sealed vessel. The headspace was then diluted with air to mimic the situation when a container of food is opened and the volatiles are diluted by the surrounding air. Because this first volatile signal can influence overall flavor perception, the parameters controlling volatile release under these conditions are of interest. A mechanistic model was developed and validated experimentally. Release of compounds depended on the air-water partition coefficient (K(aw)) and the mass transport in both phases. For compounds with K(aw) values <10(-)(3), K(aw) was the factor determining release rate. When K(aw) was >10(-)(3), mass transport in the gas phase became significant and the Reynolds number played a role. Because release from packaged foods occurs at low Reynolds numbers, whereas most experiments are conducted at medium to high Reynolds numbers, the experimentally defined profile may not reflect the real situation.     

Influence of electrolyte composition and pH on cadmium sorption by an acid sandy soil

Extraction of soil with CaCl₂, has been recommended as a measure of bioavailability of heavy metals. Interpretation of soil extraction data in terms of plant uptake potential may improve when the chemical behaviour of heavy metals in these extracts is ascertained. The effect of pH, Cd complexation by Cl, and competition between Cd and Ca on Cd sorption was studied at an ionic strength of 0.03 m . Sorption of cadmium was measured in 0.01 m CaCl₂, in 0.01 m Ca(NO₃)₂, in a mixture of 0.02 m NaCl and 0.01 m NaNO₃, and in 0.03 m NaNO₃, at different values of pH ranging from 3.8 to 4.9. Adsorption isotherms were all linear, with a negative intercept on the y-axis. This intercept indicated (linear) desorption of only part of the initial soil Cd content. About 50% of the Cd in solution was complexed in the presence of 0.02 m Cl at ionic strength of 0.03. Due to competition between Cd and Ca, sorption of Cd was reduced by 80% in the Ca-electrolytes as compared with the Na-electrolytes. Sorption was highly sensitive to pH as each 0.5 unit increase in pH resulted in twice as much sorption of Cd. An empirical factor in the sorption equation that accounts for this effect of pH showed a similar response to changes in pH as a mechanistic factor. This mechanistic factor was developed by assuming that Cd and protons sorb onto the same sites and that a two-site Langmuir sorption isotherm for protons was able to describe the titration curve of the soil. This similarity may explain the successful application of the empirical factor in this and previous studies.     

Removal of Arsenic from Aqueous Solutions by Sorption onto Sewage Sludge-Based Sorbent

This study aimed at evaluating and comparing the removal of arsenic from solutions by a low-cost waste-based sorbent, produced by pyrolysing sewage sludge under appropriate conditions, and by a commercially activated carbon. Batch sorption experiments were performed under isothermal conditions (20°C), in order to evaluate the effect of pH on the arsenic sorption kinetics and on the equilibrium sorption capacity of the materials under study. Kinetic data revealed that the arsenic sorption was faster onto the activated carbon than onto the pyrolysed sludge. The sorption process was well described by both the pseudo-first and pseudo-second-order kinetics equations for both materials. Changes in the initial solution pH have distinct effects on the removal of arsenic onto pyrolysed sludge and activated carbon. While for pyrolysed sludge, pH affects essentially the equilibrium time, for activated carbon it affects the sorption capacity. Equilibrium results were well described by both Freundlich and Langmuir isotherm models, although fittings corresponding to the Langmuir isotherm were slightly better. The Langmuir maximum sorption capacity determined for the pyrolysed sludge was 71???g?g^?1, while for activated carbon was 229???g?g^?1. Despite the relative lower capacity of the pyrolysed sludge, the considerable lower cost and the valorisation of the sludge may justify further research on its use for water decontamination.