New methods to assess water diffusion in amorphous matrices during storage and drying

Water diffusion coefficient is an important parameter for food processing and stability, strongly influenced by the composition and the physical state of the matrix (amorphous glassy or rubbery/crystalline). In this study, two different methods to assess water diffusion in amorphous matrices were compared. First, an automatic sorption device was used to measure the water sorption kinetics of powders of maltodextrin DE21 and DE47 with defined shapes when equilibrating at different air relative humidity (0–60% at 25 °C). Calculation of water diffusion coefficients was done according to Crank’s and Weibull’s models, and it was not possible when powders undergo glass transition. In the second part of the study a thin film dryer was used to assess the drying kinetics of aqueous solutions of maltodextrin (DE 6-12-29-40). The Yamamoto’s model allowed calculating water diffusion as a function of water content and temperature, above and below glass transition temperature.     

Polymer-Water Interaction of Maltodextrins. Part I: Water Vapour Sorption and Desorption of Maltodextrin Powders

Polymer-water interactions of a low DE maltodextrin and its P _n fractions are investigated by water vapour sorption and desorption measurements. The interpretation of the isotherms was done by the application of the three parameter Guggenheim-Anderson-de Boer equation and by the Flory-Huggins theory. The polymer-water interactions of the maltodextrin and its fractions exhibit strong dependence on P _n. The monolayer water content, the water uptake up to a_w 0.95, the hysteresis effect, the water content of the transition powder-gel under sorption conditions and the ability to form gels decrease with decreasing P _n. The water uptake above a_w 0.95, the monolayer sorption enthalpy and solubility increase with decreasing P _n. The participation of molecular different fractions of the maltodextrin in polymer-water interaction depends on the polymer concentration. Shelf live conditions for the maltodextrin are derived.     

Review characterization of edible films formulated with sodium alginate and low-methoxyl pectin in osmotic dehydration applications

The aim of this work was to evaluate the behaviour of two edible films (sodium alginate and low-methoxyl pectin) under different osmotic conditions (solutions: sucrose, glucose syrup and maltodextrin; concentrations: 40 °Brix and 60 °Brix; temperature 40 °C and processing times: 0.5, 1 and 2 h). From the experimental water loss and solid uptake kinetics, effective diffusion coefficients and the dehydration performance ratio were obtained. The microstructural characteristics of the osmodehydrated films were also analysed using pear as a food matrix. The results showed that films osmodehydrated with maltodextrin and glucose syrup solutions presented higher dehydration performance ratio values than those osmodehydrated with sucrose. A reduction in the thicknesses of edible coatings was observed. The best formulation was sodium alginate 2% and calcium lactate 5% according to the microstructural analysis and structural integrity for at least up to 16 h of osmotic dehydration.     

Evaluation of diffusion coefficients in osmotic concentration of bananas (Musa Cavendish Lambert)

The effect of time of exposure, solution concentration and temperature on the osmotic concentration of banana (slices of 11 mm thickness) was studied in aqueous sucrose solutions. the selectivity of the cellular tissues was reduced by steam blanching the banana slices before osmotic treatment. Effective diffusion coefficients for the loss of water and the increase in sucrose content were determined according to Fick's Law applied to a two-dimensional body; calculated on the basis of the concentration of various components in the liquid phase impenetrating the fruit. These coefficients revealed values similar to binary diffusion coefficients for pure sucrose solutions.     

Properties and release kinetics of pine bark incorporated agar and carrageenan film

Effects of plasticisers (glycerol, sorbitol and polypropylene glycol) and blend ratios on release behaviour, molecular vibration, mechanical and water barrier properties in agar and carrageenan films incorporating pine bark extract were investigated. Infrared spectra indicated hydrogen bonding of sorbitol and polypropylene glycol with film polymers which improved water diffusion and agar solubility but showed no effect in carrageenan films due to high water affinity. Hydrophilicity of the plasticisers modified dissolution of films and strongly affected the release behaviours of polyphenols and antioxidant capacity (DPPH• and FRAP). Film solubility showed high correlation to release behaviours. Fick’s diffusion kinetics fitted well to release behaviour of pine bark to aqueous media (water, 3% acetic acid and 10% ethanol). Agar gave a higher diffusion coefficient that was improved by the addition of sorbitol and polypropylene glycol. Increased diffusion coefficients enhanced degree of release, with some diversions suggesting that solvent modified matrices and, hence, release properties.     

Modeling water uptake in a cereal grain during soaking

A diffusion equation to describe the isothermal absorption of liquid water in a spherical solid that undergoes uniform swelling was derived. The resulting partial differential equation was solved using a finite difference method, taking into consideration water content dependence of the diffusion coefficient. The developed model was applied to simulate the water uptake of brown rice for the soaking temperatures of 25, 45, 55 and 65 °C. The estimated “differential” diffusion coefficients were a strongly increasing function of moisture content for all temperatures tested, approaching to the self-diffusion coefficients of water for brown rice moisture contents near to the saturation values. The “integral” diffusion coefficient corresponding to range of moisture content resulting from soaking conditions were calculated and correlated according to Arrhenius equation with an activation energy of 32.5 kJ/mol.     

Utilization of Fick's second law for the evaluation of diffusion coefficients in food processes controlled by internal diffusion

Several processes in the food industry, such as leaching and drying are usually controlled by internal diffusion. In many cases these processes have been interpreted on the basis of constant diffusion coefficients calculated through a series solution of Fick's second law which converge rapidly for large values of time. This work presents a numerical solution of Fick's second law for various types of concentration dependence of the diffusion coefficient. The results indicate that the above mentioned conventional treatment of experimental data, may not be sufficient to establish whether or not the process is characterized by a constant or variable diffusion coefficient.     

响应面法优化柿叶总黄酮的超声波辅助提取条件

利用响应面法(Response surface methodology,RSM)优化柿叶总黄酮的超声波辅助提取条件。以提取温度、乙醇体积分数、液固比、提取时间为试验因子,以柿叶提取物中总黄酮含量为响应值,采用Box-Behnken试验设计进行试验。结果表明,提取温度对总黄酮含量影响最大,其次为液固比、乙醇体积分数和提取时间。柿叶总黄酮的最佳超声波辅助提取条件为:温度53℃、乙醇体积分数69%、液固比21∶1、提取时间32min。在此条件下,柿叶提取物总黄酮含量的预测值为35.05mg/g,验证试验所得总黄酮的含量为35.36mg/g。回归方程的预测值和试验值差异不显著,所得回归模型拟合情况良好,达到设计要求。因此,超声波辅助提取法能提高提取效率、缩短提取时间和保护有效成分,具有一定的实际应用价值。     

A Study of the Physico-chemical Behavior of Diacetyl in Hydroalcoholic Solution With and Without Added Catechin and Wood Extract

The interactions of diacetyl and ethanol in model solutions were studied in order to improve understanding of the changes in flavor perception that occur during both alcoholic beverage processing and consumption. A gradual reduction was demonstrated in the activity and partition coefficients of diacetyl as the ethanol concentration in aqueous solutions increased. From a sensory point of view, this fact would be expected to cause an increase in the diacetyl sensory thresholds. The expected diacetyl sensory thresholds were calculated based on experimental determination of the diacetyl vapor pressure in ethanol-water solutions at different ethanol concentrations. These sensory thresholds were not measured but merely obtained by theoretical interpolations. No significant variations in the activity coefficients of diacetyl were observed in the presence of catechin. Conversely, the dissolution of wood extract at 40% ethanol caused a significant decrease in diacetyl vapor pressure. The addition of catechin and wood extract to 40% ethanol-water solution contributed to the interactions of ethanol and water measured by DSC analysis.     

The effect of sugars on the diffusion of water in starch gels: a pulsed field gradient NMR study

The self-diffusion coefficient of water was measured in starch–sugar–water systems of various compositions. The starch was either waxy maize or potato starch and the sugar was either sucrose or xylose. The diffusion results obtained from sugar solutions (i.e. with a zero polymer concentration) suggested that a free water behaviour should only be expected after a bilayer coverage of the sugar molecule. The presence of sugars was found to decrease considerably the translational mobility of water in starch gels. This reduction was proportional to the sugar concentration in the system but showed little dependence on the type of sugar. An attempt was made to relate the self-diffusion coefficients of water in starch–sugar–water gels to those obtained for the individual binary systems (starch–water and sugar–water). A prediction based on the additive effects of sugar and starch only corresponded with experimental results in dilute systems.     

喷雾干燥法制备无花果微胶囊的研究

以阿拉伯胶和麦芽糊精为壁材,以无花果的乙醇提取物为芯材,用喷雾干燥法制取无花果微胶囊粉。通过正交试验分析,确定了最佳生产工艺条件:芯材与壁材的比例为1:4,阿拉伯胶与麦芽糊精的比例为1:1,固形物浓度为30%,乳化剂用量为0.3%,30 MPa均质2遍,进风温度为200℃,出风温度为81℃。生产出的微胶囊无花果粉色泽、溶解性好,水、表面油含量低,无甚粘壁现象,适合于工业化生产。     

Comparison of Conventional and Ultrasound Assisted Extraction Techniques of Yellow Tea and Bioactive Composition of Obtained Extracts

Yellow tea is the least investigated type of tea (Camellia sinensis), therefore, this study is focused on characterization of bioactive content of yellow tea extracts as well as application of inovative extraction techniques (ultrasound bath and probe) compared to conventional extraction, in water and aqueous ethanol media. Comparison of obtained extracts was based on total flavonoid (TFC) and nonflavonoid (TNC) content, HPLC analysis of individual polyphenols and methylxanthines, and antioxidant capacity. The highest TFC was detected in extracts obtained by ultrasound probe assisted extraction in aqueous ethanol as an extraction medium and the lowest in extracts obtained by ultrasound bath extraction (water and aqueous ethanol) with a trend of increase with prolonged extraction time. Conventional extraction was successful when combined with 75% aqueous ethanol as an extraction medium. Results of HPLC analysis and antioxidant capacity assays were generally in compliance with these results. This study proves that ultrasound probe extraction could succesfully be used for extraction of polyphenols and methylxanthines from yellow tea.     

Extraction of ginger rhizome: kinetic studies with dichloromethane, ethanol, 2-propanol and an acetone—water mixture

The kinetics of extraction of [6]-gingerol from ground Jamaican ginger rhizome have been determined at 30°C in dichloromethane, ethanol, isopropanol and an 80% (v/v) acetone + 20% (v/v) water mixture. The extractions all proceeded in three stages: an initial 'washing' stage, a fast stage and a subsequent much slower stage. The rate of extraction of hexahydrocurcumin in ethanol was found to follow a simpler pattern. From the first order plots, the diffusion coefficients of the extracted solubles within the ginger particles were calculated. They varied inversely with the 0.6 power of the solvent viscosity, which explained why the rates of [6]-gingerol extraction decreased in the sequence: acetone < acetone + water < dichloromethane < ethanol < isopropanol. These results show that solvents of low viscosity should be chosen to attain fast extraction rates. The diffusion coefficient of [6]-gingerol was also measured at 30°C in pure acetone, ethanol and isopropanol. The values in these bulk solvents were 13–20 times greater than the diffusion coefficients of [6]-gingerol within the ginger particles for the fast stage and over 900–1800 times greater than those for the slow stage. These hindrance factors quantify the effect of the ginger matrix environment on internal diffusion.     

Diffusion of 22Na and 85Sr in montmorillonite: evidence of interlayer diffusion being the dominant pathway at high compaction

A mechanistic understanding of transport phenomena in compacted clays is essential for the use of such materials as engineered barrier systems for the safe geological disposal of radioactive wastes. The present contribution is a first step in the development of an integrative treatment of the properties of tracer cations in compacted bentonites with respect to diffusion and sorption. The diffusion of 22Na and 85Sr in highly compacted montmorillonite and kaolinite is investigated as a function of the "external salt concentration" (NaClO4), i.e., of the solution in equilibrium with the clay. Consistent results were obtained from through-diffusion experiments and tracer profile analysis. Knowledge of genuine diffusion coefficients of the filter plates turned out to be crucial in cases where the diffusive resistance of the filter plates was similar to that of the clay. Diffusion coefficients formally calculated on the basis of the tracer concentration gradient in the external aqueous phase, and the sorption distribution ratios were found to decrease with increasing external salt concentration in the case of montmorillonite. In a logarithmic representation of these data, a slope of -1 was obtained for the monovalent 22Na, whereas the slope was -2 for the divalent 85Sr. In the case of kaolinite, diffusion coefficients were independent of the external salt concentration. It is postulated that the diffusion of the tracer cation through the interlayer water is the dominant pathway in compacted swelling clays under the experimental conditions tested. Effective diffusion coefficients, based on a tracer concentration gradient in the interlayer water of the clay, were found to be independent of the composition of the external aqueous phase. The latter gradient is assumed to be a function of the external salt concentration, according to a calculated distribution of the tracer cation between free pore water and the interlayer water via cation exchange.     

RELEASE OF PROPYL PARABEN FROM A POLYMER COATING INTO WATER AND FOOD SIMULATING SOLVENTS FOR ANTIMICROBIAL PACKAGING APPLICATIONS

The release phenomena of propyl paraben from a polymer coating to water and three food simulating solvents (10% aqueous ethanol, 50% aqueous ethanol, n-heptane) were studied for antimicrobial packaging applications. The effects of food simulating solvent, initial concentration in the coating and temperature on the propyl paraben release were examined. The initial concentration of propyl paraben in the coating ranged from 1.26 × 10⁴ to 10.52 × 10⁴ g/m³ and the temperature from 5.5 to 30C. For water, the release was controlled by Fickian diffusion with constant diffusion coefficient (7±11 × 10^-11 cm²/s at 30C), and independent of the initial concentration. For 10% ethanol, the release followed again the Fickian model with constant diffusion coefficient (30±40 × 10^-11 cm²/s at 30C). For 50% ethanol and n-heptane, the release was instantaneous and not controlled by Fickian diffusion. For the release into water, the activation energy for diffusion from the Arrhenius relationship was around 88 kJ/mole.     

CFD Modeling and Simulation of Maltodextrin Solutions Spray Drying to Control Stickiness

Particle stickiness during spray drying can lead to operational problems or be used to perform agglomeration inside the chamber. A simplified computational fluid dynamics approach is proposed to simulate the spray drying of 40% w/w aqueous solutions of maltodextrin DE12 and DE21 in a pilot cocurrent spray dryer equipped with rotary atomizer. Drying was simulated at steady state considering the geometry of the equipment (drying chamber, air inlet, atomizer) and the close relation between drying air and product properties. To take into account the lower drying rate of liquid solutions compared to pure water, the water vapor pressure of the drying particles was decreased with a coefficient determined from experimental data on air temperatures and humidities measured in the chamber. The evolution of particle temperature and water content was simulated. From these values and glass transition temperatures of the considered materials, it was possible to determine zones and operating conditions for which particles could be sticky inside the chamber. Maltodextrin DE12 was quickly dried close to the atomizer reaching a stable nonsticky state below glass transition temperatures Tg, while maltodextrin DE21 with lower Tg could exhibit a sticky behavior in a wider part of the chamber, depending on the liquid flow rate. This approach provides a methodology to evaluate possible stickiness to avoid fouling of the plant or to optimize powder insertion position for agglomeration.     

Influence of carrier agents on the physicochemical properties of blackberry powder produced by spray drying

The aim of this work was to study the effect of different carrier agents (maltodextrin, gum arabic or a blend of both carrier agents) on the physicochemical properties of blackberry powder produced by spray drying. Moisture content, anthocyanin retention, antioxidant activity, colour parameters, bulk and absolute density, porosity, wettability, sorption isotherms, particle size and morphology of blackberry powders were evaluated. The use of maltodextrin resulted in less hygroscopic powders with lower moisture content and better reconstitution properties. Powders produced with maltodextrin or a blend of maltodextrin and gum arabic presented the best anthocyanin retention and the highest antioxidant activity. Experimental data of water adsorption were well fitted to GAB model. All the samples exhibited a large number of irregular particles with spherical shapes. However, particles produced with gum arabic were smaller and showed more dented surfaces, which probably contributed to the increase in wettability values and lower pigments retention.     

面糊组分对预油炸微波复热鸡米花品质及水分分布特性的影响

针对鸡米花在微波复热过程中水分“外迁”和油分“外浸”造成脆性降低的问题,研究不同面糊组分,羟丙基羧甲基纤维素（hydroxypropyl methylcellulose,HPMC）和麦芽糊精对预油炸及微波复热后鸡米花含油量、含水量及分布、脆性、颜色、感官品质的影响,以期提高鸡米花微波复热后的脆性及品质特性。结果表明,面糊中添加2%?HPMC和6%麦芽糊精显著降低了微波复热后鸡米花外壳中含水量的增加以及内芯肉中含水量的减少（P＜0.05）,同时使内芯肉T22向快弛豫方向移动,降低了自由水的移动性,同时微波后A22显著高于对照组（P＜0.05）,抑制微波过程中内芯肉中自由水向外壳的迁移,从而保证微波复热后鸡米花外壳脆性和内芯肉多汁性;添加2%?HPMC、6%麦芽糊精及两者复配的微波复热鸡米花外壳脆性较对照组均显著提高（P＜0.05）;但添加2%?HPMC的鸡米花外壳硬度最大,添加6%麦芽糊精的鸡米花含油量最高（P＜0.05）。当面糊中同时添加2%的HPMC和6%的麦芽糊精时,鸡米花经微波后其外壳脆性最好,硬度适中且无油腻感。该研究结果为裹粉类微波食品脆性及品质的改善提供了数据基础。     

Effect of freezing rate on quality parameters of freeze dried soursop fruit pulp

The effect of freezing rate on the final moisture and ascorbic acid content, water solubility, wettability and color of freeze dried soursop fruit pulp treated with maltodextrin was studied. Different size ice crystals derived from distinct freezing rates origins diversity of product specific surface area that influence both water desorption and water dissolution, but in opposite manners. After a constant drying time of 6 h the moisture content of the dried samples was in the range of 8.68–13.09% being higher for higher values of freezing rate. An inverse linear dependence between initial freezing rate and final water solubility (85.75–81.51%) of freeze dried samples was also found. Faster freezing rates also affected the wetting time (0.36–1.26 min) because they produced decreasing in pore size and simultaneously increasing in capillary tortuosity of the final micro-structure of the dried samples. Freeze-dried powders were much brighter in color compared to the maltodextrin treated pulp. Among the freeze dried samples, those prepared with higher freezing rates were lighter in color.     

大黄鱼鱼卵油微胶囊制备工艺及其性质表征

为实现大黄鱼鱼卵油高值化利用,本研究以大黄鱼鱼卵油为芯材,辛烯基琥珀酸淀粉钠复配麦芽糊精为壁材,采用喷雾干燥法制备大黄鱼鱼卵油微胶囊。在单因素实验基础上,以大黄鱼鱼卵油包埋率为指标,通过响应面法优化大黄鱼鱼卵油微胶囊的制备工艺;进一步对最优条件下所得的大黄鱼鱼卵油微胶囊的水分含量、溶解性、堆积密度、休止角及微观结构进行了表征。结果表明:在辛烯基琥珀酸淀粉钠/麦芽糊精复配比为1:1、固形物含量为20%、芯壁比为1:1.5、进风温度为80℃时,大黄鱼鱼卵油微胶囊包埋率可达到97.87%;在此条件下得到的大黄鱼鱼卵油微胶囊水分含量为1.1%、溶解性为47.56%、堆积密度为0.718 g/cm3、休止角为32.47°,微观结构表征显示其颗粒细小均匀、近球形、表面致密、无裂缝。研究结果可为大黄鱼鱼卵油的高值化利用提供理论指导。