Kappa carrageenan fluid gel material properties. Part 2: Tribology

Semi-solid and liquid food thickeners typically take the form of either polymeric or particulate structures. These structures are known to control flow properties and mixing efficiency which can influence performance, texture and the perception of tastants and aromas. However, their structural influence on thin-film rheology (tribology), which is also relevant for texture perception, is not so well understood. In this investigation, the tribology in a boundary regime of lubrication is tested using kappa carrageenan lubricants formulated both in solution and as gelled particles in suspension (fluid gels) to provide new insights into the structural influence of thickener type on tribology. Polymeric lubricated systems were shown to be dominated by elastic deformation of the tribo surfaces and particulate suspensions were dominated by particles acting as contacting asperities of the mating surfaces. The tribology of gelled particles was shown to depend strongly on particle elasticity where less deformable (stiffer) particles reduce surface–surface contact and therefore reduce friction coefficients. The effect of particle volume fraction on friction coefficient is related to the number of particles entraining the contact and not particle–particle interactions or bulk rheological behaviour.     

Effect of typical sugars on the viscosity and colloidal stability of apple juice

Cloudy apple juice may be modeled as a dilute colloidal dispersion of solid particles in a solution of pectins, sugars, organic acids, and salts. In order to evaluate the effect of sugars on the viscosity and stability of the juice, it was diafiltered by ultrafiltration to remove the native soluble solids, and controlled amounts of sugars (glucose, sucrose, and maltose) were added afterwards. The addition of sugars produced a linear increase of the specific viscosity at decreasing water activities. The rates of increase (slopes) were proportional to the hydration capacity of each sugar. The specific viscosity of a colloidal dispersion of solid particles in sugar solution depends on three types of interactions: particle–particle (p–p), particle–water (p–w), and particle–sugar (p–s). P–p and p–w interactions were estimated from the extended DLVO theory in terms of the energy barrier between pairs of particles, and found to decrease at increasing sugar concentrations. Then, the increase of the specific viscosity was attributed to an increase of p–s interactions. The total energy barrier of the system (a measure of its stability) was modeled to be the sum of a p–p (including p–w) contribution plus a p–s contribution, and estimated from specific viscosity vs. particle volume fraction data at different sugar concentrations. The p–s contribution was estimated by difference. It was found to be positive (which was attributed to hydration repulsion) and higher than the p–p contribution at sugar concentrations ?0.04 mol/mol.     

The effects of freezing on soybean microstructure and qualities of soymilk

This study was to investigate the effects of freezing on soybean microstructure and the qualities of soymilk made from the soybean by direct grinding in water without soaking. Transmission electron microscopic (TEM), particle size distribution determination and SDS–PAGE were used for the examination. TEM images showed that freezing treatment could induce the coalescence of protein storage vacuoles (PSVs) and oil bodies. Particle size distribution showed a trend that prolonging of freezing could decrease the average particle size of soymilk and increase the extraction efficiency of soybean. SDS–PAGE showed that extractable proteins were mainly composed of glycinin and β-conglycinin even after freezing. After freezing, soybean could be easily stored and could be used to make soymilk without soaking. The soymilk had a higher solid content and better stability than the soymilk from soybean without treatment. Thus, this study provided a convenient and short-time way to process soymilk at home.     

Particle crystallization during spray drying in humid air

A new and modified spray drying setup was arranged to produce spray-dried crystalline lactose particles. According to Williams–Landel–Ferry kinetics (WLF), it was suggested that a higher particle temperature and lower glass-transition temperature would increase the crystallization rate of the particles during the spray-drying process while still giving dry powders. The new experimental setup allowed the particle temperature to reach higher values by using an insulated drying chamber and also allowed the particle glass-transition temperature to reach lower values by maintaining a higher gas humidity with the aid of a condenser unit attached to the dryer. Modulated differential scanning calorimetry (MDSC) and moisture-induced sorption analysis were used to verify the crystallinity of the spray-dried lactose powders. These analyses showed a higher degree of crystallinity for the particles than have previously been reported in the literature. X-ray diffraction and Raman spectroscopic analyses were further used to identify different lactose anomers. The results suggest that only α-lactose anomer exists in the products as obtained from the modified spray-drying system. The micrographs from scanning electron microscopic analysis also indicated a very crystalline nature for the particles.     

LIQUID-TO-PARTICLE HEAT TRANSFER DURING CONTINUOUS TUBE FLOW: INFLUENCE of FLOW RATE and PARTICLE to TUBE DIAMETER RATIO1

Liquid-to-particle convective heat transfer coefficients were measured during continuous flow through tubes, using an experimental technique in which a thermocouple was moved at the same speed as the particle. Water was used as the carrier fluid and transducer particles were made hollow to approximate densities of real food particles. Results from over 250 experimental runs over a fluid Reynolds number range from 7300 to 43600, showed that the convective coefficient was increased significantly with increasing fluid flow rate and particle to tube diameter ratio. Convective coefficient values ranged from 688 to 3005 w/m²⁰C depending on the experimental conditions. Dimensionless correlations obtained between the Nusselt number, particle Reynolds number, particle to tube diameter ratio, and the particle Froude number yielded R² values ranging from 0.82 to 0.92 depending on the complexity of the relation.     

Acoustical performance of loose cork granulates

This paper reports on an investigation of the acoustical performance of loose cork granulates. This investigation is based on the physical parameters of loose granular cork obtained through an empirical model of the acoustic properties of loose granular media shown by Voronina and Horoshenkov and the experimental performance of these granulates. The performance is assessed according to ISO 10534-2 (1998). The data obtained show clearly that this porous absorber exhibits high sound absorption performance varying with particle size. The relationship between the experimental and the model results demonstrates the existence of significant differences between particle sizes >3.5 mm. Finally, the performance of this material is compared to other granular materials.     

Using biopolymer blends for shrimp feedstuff microencapsulation — I. Microcapsule particle size,morphology and microstructure

A shrimp feedstuff was microencapsulated through spray drying using different biopolymer treatments as wall materials after a three component Simplex Centroid experimental design, employing wall material to feedstuff ratios of 2:1 and 3:1, and pH values of 4 and 8. The response surface methodology indicated that the three above mentioned variables affected the microcapsule particle size and microstructure, as evidenced by scanning electron microscopy. Predictive equations show that the factor that affected significantly the microcapsule particle size was the binary interactions among the biopolymers. The higher the wall material-feedstuff ratio the larger the microcapsule particle size. As pH varied from 4 to 8, the biopolymer adsorbed layers around the core material were more extended. All the resulting microcapsules were of the matrix type, in which the feedstuff microparticles were distributed within the solid wall material matrix.     

Emulsion gels: The structuring of soft solids with protein-stabilized oil droplets

Many food products can be categorized as emulsion gels. This is especially the case for protein-based oil-in-water emulsions which can be converted into soft-solid-like materials by common food processing operations such as heating, acidification, and enzyme action. This review article outlines how the rheological and structural properties of protein-stabilized emulsion gels are influenced by the dispersed oil volume fraction, the oil–water interfacial composition, and the colloidal interactions of the constituent emulsion droplets. For model systems of variable oil content and containing different food proteins, some general trends of rheological behaviour at small and large deformations are identified. Experimental rigidity data are considered in relation to: (i) material science theories of the reinforcement of solid materials by active and inactive filler particles, and (ii) Brownian dynamics simulations of aggregated particle networks containing bonded and non-bonded particles. Influences of interfacial composition and particle–matrix interactions on microstructure and rheology are explained with particular reference to the role of small-molecule surfactants. Compositional and structural factors affecting the large-deformation rheology and fracture properties are described. Finally, the practical relevance of the model system studies to the behaviour of real food products is critically assessed.     

A rapid HPLC post-column reaction analysis for the quantification of ergothioneine in edible mushrooms and in animals fed a diet supplemented with extracts from the processing waste of cultivated mushrooms

For establishing an efficient and sensitive method for the quantitative determination of 2-thiol-l-histidine-betaine (ergothioneine, ERG) in edible mushrooms and the blood and muscles of animals, a technique using reversed-phase separation and post-column reaction between 2′-dipyridyl disulphide and ERG was developed. A corresponding derivative 2-thiopyridone, detected at 343 nm, was used for estimating ERG concentration. The flow rate, temperature, pH, and composition of the solution were optimised. A low limit of quantification (1.41 ppm) and a simpler sample preparation made this technique more rapid compared to other methods using liquid chromatography–mass spectrometry. The coefficient of variation (CV) values for the reproducibility and recovery of ERG were within the acceptable values of 6% and 97.5–100.0%, respectively. The efficiency of this methodology was compared with that of spectrophotometric and mass-spectrometric quantitative methods, and was assessed in the light of previous studies. The ERG contents in different mushrooms were 12.69–234.85 mg/kg wet weight basis. Dietary supplementation with extracts from mushroom processing waste significantly improved ERG bioavailability in the blood of yellowtail fish and muscle tissue of cattle.     

球形中空微粒的可见光消光特性

根据Aden-Kerker理论,研究了球形中空微粒的散射特性。利用MATLAB编程,对球形中空微粒在可见光波长范围内的消光性能进行数值模拟,详细分析了中空微粒的外层折射率、尺度参数、壁厚等对其消光性能的影响。结果表明：随微粒外壳相对折射率的增加,其消光系数先减小后增大;随微粒尺度参数的增大,消光系数则呈现震荡并出现一系列极大极小值,最后振幅减弱并在2附近上下波动;随微粒壁厚的减小,消光系数一般先增大后减小。实际应用中可以利用中空微粒不同的直径和壁厚组合来实现某一特定的消光作用,且一般空心微粒的消光作用优于实心微粒。     

近红外光谱测定苹果饮料中原果汁含量

提出了一种遗传算法优化支持向量机参数的近红外光谱技术对苹果饮料中原果汁含量的快速测定方法。在确定光谱数据预处理方法的基础上,通过遗传算法对支持向量机(SVM)预测模型的各项参数进行寻优,将优化出的参数代入SVM预测模型中,得到基于遗传算法的SVM模型,利用此模型对苹果饮料中原果汁含量进行预测研究。结果表明,建立的SVM模型对预测集的决定系数为0.9757,能快速测定苹果饮料中的原果汁含量。      

不同壁材制备油茶籽油微胶囊的研究

研究以大豆分离蛋白、酪朊酸钠、麦芽糊精、大豆膳食纤维和阿拉伯胶为壁材,通过复配组合,利用喷雾干燥法制备油茶籽油微胶囊产品,同时以乳化稳定性、微胶囊化效率和产率、微胶囊形态的微观表征颗粒完整率和微胶囊感官品质评价为评定指标,比较不同壁材组合得到的微胶囊产品之间的差异。结果表明,以大豆分离蛋白、酪朊酸钠和麦芽糊精为复配壁材的油茶籽油微胶囊产品为乳白色粉末,具有良好冲调性和流动性,微胶囊化效率83.62%和产率63.87%,微胶囊形态的颗粒完整率接近70%,是较好的喷雾干燥制备油茶籽油微胶囊产品的复配壁材之一。     

Evaluation of tube-flow fluid-to-particle heat transfer coefficients under controlled particle oscillatory motion

A previously developed particle oscillatory motion technique, with direct temperature measurement of particles in motion under tube-flow conditions, was evaluated for studying the effect of several influencing factors associated with fluid-to-particle heat transfer coefficient (h_fp). A full factorial experimental design was employed involving spherical particles made of aluminum epoxy and Nylon of different sizes (12.7–17.5 mm), different particle linear velocities (0.06–0.21 m/s), heating medium viscosities (0 to 1% concentration of carboxymethyl cellulose solution, CMC) and fluid temperatures (60–80°C). Statistical analysis of experimental data indicated that all factors investigated had a significant (P<0.001) effect on h_fp. A t-test grouping analysis showed that mean values of h_fp were different (α=0.05) among the levels of the various factors. As expected, the fluid-to-particle heat transfer coefficient increased with particle velocity and fluid temperature, and decreased with CMC concentration. In agreement with some reports, h_fp decreased with particle size. Further, the values of h_fp associated with the aluminum epoxy particle were generally higher than that for the Nylon particle of the same size. The study thus demonstrates the feasibility and usefulness of the technique for gathering tube-flow h_fp data under a range of conditions involving particle oscillatory motion.     

Efficacy of pullulan in emulsification of turmeric oleoresin and its subsequent microencapsulation

Numerous advantages of turmeric oleoresins over ground turmeric are offset by their sensitivity to light, heat, oxygen and alkaline conditions. This can be overcome by microencapsulation. The present work evaluates the efficacy of pullulan to achieve a stable emulsion of turmeric oleoresin and its subsequent microencapsulation. Different ratios of gum arabic and maltodextrin (100:0–0:100) were used to evaluate the appropriate wall material for encapsulation of turmeric oleoresin by spray drying. The emulsions were prepared at 10% loading of turmeric oleoresin, and evaluated for emulsion stability index, particle size and viscosity. The microcapsules prepared by spray drying of these emulsions were evaluated for encapsulation efficiency, encapsulation yield, and stability of volatiles, non-volatiles and total curcumin for six weeks. The efficacy of pullulan was seen from emulsion characteristics, encapsulation efficiency and yield, and t_1/2, the time required for a constituent to reduce to 50% of its initial value.     

提升管内气固流动行为的CFD-DEM模拟

采用CFD-DEM耦合模型对提升管内的气固流动进行了模拟,分析了颗粒间碰撞弹性恢复系数及摩擦系数和Saffman升力、Magnus力等因素对管内气固流动结构的影响,分析得到了提升管内有关颗粒速度、颗粒含率及颗粒拟温度等的大量数据,对数据分析后得到了提升管特有的气粒流动规律:颗粒轴向呈现上稀下浓的分布规律,径向分布规律为管中心低壁面高。同时发现当管内的颗粒碰撞为完全弹性,其分布会更加均匀,另外Saffman力、Magnus力等对颗粒运动没有明显的影响。     

Physicochemical properties of cell wall materials from apple, kiwifruit and tomato

Cell wall materials (CWMs) were isolated from the fruit of ripe apple, kiwifruit and tomato using methods of isolation which maximised the water retaining capacity and viscosity generating properties of the CWMs. Aqueous suspensions of all three CWMs were able to form a gel-like matrix at a concentration of 1%. There was a dramatic enhancement in gel firmness of kiwifruit and tomato following a high shear treatment, but no such effect was apparent with apple CWM. Confocal microscopy showed that the shear-induced increase in viscosity was accompanied by fragmentation of the CWMs of kiwifruit and tomato which increased the available surface area for particle–particle and/or particle–solvent interaction. The viscosity of kiwifruit and tomato CWM dispersions was reduced in the presence of electrolytes indicating an important role for the double electrical layer in the gelling properties of the CWMs. The viscosifying properties of apple CWM were however independent of both shear and added electrolyte. This was attributed to the fact that CWM from apple resisted breakup under high shear. The greater connective integrity of the apple cell walls compared to that of kiwifruit and tomato is discussed in relation to differences in ripening induced changes to the pectic polysaccharides of the cell walls.     

Optimisation of the formulation of β-carotene loaded nanostructured lipid carriers prepared by solvent diffusion method

In this study, the optimised β-carotene loaded nanostructured lipid carriers (NLC) were prepared using the solvent diffusion method. Response surface methodology (RSM) was employed in conjunction with a central composite design (CCD) to evaluate the effect of the preparation variables on particle size and β-carotene stability to optimise the NLC formulation. Quadratic polynomial was the best fitted mathematical model for the experimental results. The statistical evaluations revealed that the lipid phase concentration and the surfactant concentration had significant effect on particle size of NLC. In addition, the influence of the liquid lipid to total lipid ratio and temperature on β-carotene degradation was more important. The optimum formulations with minimum particle size (8–15 nm) and low β-carotene degradation (0–3%) were derived from the fitted models and were experimentally examined which demonstrated a reasonable agreement between experimental and predicted values. Transition electron microscopy (TEM) observations exhibited spherical morphology of β-carotene loaded NLC.     

基于磁电感应检测橄榄油酸价及过氧化值的研究

利用单相变压器工作原理将不同储藏期的橄榄油作为次级线圈,在室温下考察激励电压、频率和不同匝数比对橄榄油的电学特性影响,结果发现随样品的酸价和过氧化值提高其终端电压也增高,频率对不同样品的终端电压无显著影响,橄榄油的酸价和过氧化值可采用终端电压进行量化,激励电压为25 V时酸价和终端电压呈现线性关系且决定系数最高为R2=0.998,而激励电压为20 V时过氧化值和终端电压呈现2项式函数关系且决定系数最高为R2=0.991,采用130个不同酸价和过氧化值的样品对回归方程进行校验发现样品的酸价和过氧化值的预测值和实际值的相关系数分别为r=0.948和r=0.974,通过施加交变磁通来考察橄榄油的电学参数可作为一种潜在的快速检测其酸价和过氧化值的方法。     

Activity coefficients in the evaluation of food preservatives

Food preservatives are used in very low concentrations. However, usually they are used in aqueous high ionic strength solutions. The Pitzer model allows activity coefficient determination in these cases. Without the knowledge of activity coefficients, activity or ‘correct concentration’ cannot be known. In this work, the activity coefficients of sodium chloride, potassium chloride and calcium chloride in pure solutions were calculated by the Debye–Hückel theory and the Pitzer theory. The calculated values were compared with experimental values. Activity coefficients of pure sodium benzoate in aqueous mixed solutions with potassium chloride or calcium chloride were evaluated using the Pitzer model. The same evaluation can be done to more complex systems once all Pitzer parameters values for the ionic species are known.     

Effect of processing conditions on physicochemical properties of astaxanthin nanodispersions

A top-down approach based on an emulsification–evaporation technique was used to prepare nanodispersions of astaxanthin. Response-surface methodology was employed to investigate the effect of the main processing conditions, namely, the applied pressure (20–90 MPa), number of cycles (0–4) and evaporation temperature (16–66 °C), on the average particle size, polydispersity index and astaxanthin concentration of the nanodispersions. Second-order polynomial regression models expressing the astaxanthin nanodispersion properties as functions of the main processing variables were significantly (p < 0.05) fitted, with high coefficient-of-determination values (R² > 0.90). A multiple-optimisation procedure showed that the optimum conditions of pressure, number of cycles of homogenization and evaporation temperature, were 50 MPa, two cycles and 47 °C, respectively. A statistical assessment showed insignificant (p > 0.05) differences between experimental and predicted values, thus verifying the adequacy of the final reduced models fitted for explaining the variation of emulsion properties, as a function of homogenization and evaporation conditions.