MODELING RHEOLOGICAL BEHAVIOR OF GELATINIZING STARCH SOLUTIONS USING MIXER VISCOMETRY DATA

A Brookfield RVTD mixer viscometer was used to gelatinize 5.5, 6.4, and 7.3% (d.b.) native corn starch solutions, and a 6% bean starch solution. Torque, the dependent variable, was used to estimate parameters in a generalized viscosity model. The independent variables were impeller speed, temperature (50–95°C), concentration, temperature-time history, and strain history. The starch dispersions thickened with decreasing temperature and had an Arrhenius activation energy between 6.4 and 12.7 kJ/mol. There was no evidence that retrogradation caused this effect. First-order reaction kinetics was accurate (9.8% standard deviation) in describing viscosity increase during gelatinization. After initial gelatinization, torque decayed exponentially with time. Predicted curves followed experimental pasting curves when interactions among the independent variables were accounted for in the model. The major variables controlling the pasting process were temperature-time history before peak torque, strain history between peak torque and cooling, and temperature during cooling.     

SOLUBILIZATION OF AQUEOUS SOLUTIONS IN NONPOLAR LIQUIDS

ABSTRACT— Water was solubilized in orange oil, soybean oil, benzyl alcohol, n-heptane, n-hexane and cottonseed oil. Using dioctyl sodium sulfosuccinate, aqueous ascorbic acid was solubilized in orange oil, soybean oil, benzyl alcohol, n-heptane and n-hexane. Triglycerol monooleate and decaglycerol dioleate, or caprylic acid and ethoxylated stearic acid solubilized aqueous ascorbic acid in cottonseed oil. Solubilization applications are suggested.     

PEG/(NH4)2SO4双水相萃取法提取果胶酶的研究

对PEG（聚乙二醇）／（NH4）2SO4。双水相提取果胶酶进行了研究，考察了PEG分子量、pH、成相物质浓度、NaCl浓度、温度等因素对果胶酶分配系数的影响，结果表明：双水相最佳提取条件为PEG 100027％，（NH4）2SO419％，Na-Cl0．002％，pH5．0，温度50℃，在此条件果胶酶分配系数可达到14．0。     

RHEOLOGICAL PROPERTIES OF AQUEOUS SOLUTIONS OF THE GUMMY EXUDATE OF ZANTHOXYLUM TESSMANNII

Some factors that affect the rheological properties of the aqueous solutions of zanthoxylum gum were studied. The solutions exhibited Newtonian flow at low concentrations, becoming pseudoplastic as concentration increased. It was impossible to obtain a completely wetted mass at concentrations above 25% w/v. The viscosity of the gum solutions reduced irreversibly on storage and when stored at elevated temperature. However, an increase was observed with decrease in storage temperature with the solution turning into a stable gel at 4°C. The gum solutions exhibited characteristics of an acidic polyelectrolyte at dilute concentrations and in the presence of acid and salts. The expected increase in viscosity with added base was not obtained. A thick gel layer formed at interfaces between the gum solution and air, and containers and closures made with polymeric materials. This was attributed to the adsorption and interaction of the gum molecules at these interfaces.     

7–THE LIQUID RETENTION OF REDUCED WOOLS IN AQUEOUS SOLUTIONS

An investigation is reported in which samples of wool fabric were converted to the thiol, S-carboxymethyl, and S-aminoethyl forms by reduction with tributylphosphine and alkylation with either iodoacetate or bromoethylamine. The liquid retention of the samples was measured after immersion in aqueous solutions at 20°C under various conditions of pH and ionic strength.

Plots of liquid retention against pH for the different samples are explained on the basis of the net charge on the sample at a given pH. Untreated wool has a liquid retention of 38–45% (w/w) throughout the pH range examined, whereas the treated wool samples all have maximum liquid retentions of more than 150% at pH values distant from their iso-electric points. Liquid retentions of less than 50% are observed at the iso-electric points of the various samples. The extent of liquid retention of reduced wools is shown, in most instances, to diminish with increasing ionic strength of solution.

Wool fabrics in which a small fraction of the disulphide cross-links has been broken also show slightly increased liquid retention. The importance of cross-link breakdown and electrostatic-charge balance on swelling during wool processing is discussed.     

STABILITY OF INOSINIC ACID, INOSINE AND HYPOXANTHINE IN AQUEOUS SOLUTIONS

The stability of inosinic acid. inosine and hypoxanthine in aqueous solutions at 90°C was studied. Inosinic acid, inosine and hypoxanthine were separated by ion exchange chromatography and spectrometrically estimated. Reaction rates in the region pH 2–12 were calculated. The activation energy at pH 3, 4 and 5 were 34.0, 30.4 and 28.1 kca1/mol, respectively. Results show that inosinic acid contents of heat-preserved meat products and enzyme-free systems would stay practically unchanged during normal storage conditions.     

A GAS CHROMATOGRAPHIC PROCEDURE FOR ANALYSIS OF AQUEOUS ORANGE ESSENCE

SUMMARY– A procedure for direct GLC analysis of orange essence was developed. The procedure uses a Porapak precolumn to separate the water, methanol, acetaldehyde and ethanol from the remainder of the volatile organic constituents of the essence. Determination of the organic material in the essence can be obtained by this method from a 25 μl sample of aqueous essence. The method allows a quantitative estimation of acetaldehyde, methanol and ethanol as well as the smaller amounts of other organic compounds in the essence.     

MODELING OF THICKNESS FOR SEMISOLID FOODS

We investigated the relationship between orally perceived thickness and calculated shear stress on the tongue for mayonnaise and custard. To this end, the applicability of the models of Kokini et al. (1977), describing the mechanical breakdown in the mouth, have been tested. Within a limited range of shear stresses (mayonnaise < 150 Pa; custard < 30 Pa), there was a linear relationship between shear stress and thickness, in accordance with the work of Kokini et al. (1977). Beyond this range, the linear relationship breaks down and the thickness levels off with shear stress for both mayonnaise and custard. The relationship over the entire range of shear stresses used in this paper can be satisfactorily described by a semilogarithmic (Fechner) relation. For both types of products, the quality of the thickness prediction by the decreasing‐height model and the constant‐height model of Kokini et al. (1977) is similar. For most mayonnaises, the contribution of the lateral movement of the tongue to the shear stress in the decreasing‐height model of Kokini et al. (1977) is orders of magnitude larger than the contribution of the squeezing or compression movement of the tongue towards the palate. This difference in magnitude is affected by the low value measured for the compression force and by the high values for material consistency K. The values for K are high because yield‐stress behavior has been neglected when the flow curves were analyzed. For custard, the models of Kokini et al. (1977) are found to be less adequate. It is proposed that this is because the models ignore interactions with saliva. Several routes to improve the modeling by incorporating viscoelastic behavior were unsuccessful. Elongational stress and yield stress were neglected in all tested models.     

MODELING DEAD-END ULTRAFILTRATION OF APPLE JUICE USING ARTIFICIAL NEURAL NETWORK

An artificial neural network (ANN) was developed to model the dead-end ultrafiltration process of apple juice. Molecular weight cutoff, transmembrane pressure, gelatin–bentonite concentration and time were the input variables, while filtrate flux and filtrate volume were the output variables of the ultrafiltration process. According to error results and correlation values for two types of network (one or two hidden layer configurations), configurations with two hidden layers had comparatively better performance. The highest correlation coefficient with the minimum prediction error was calculated for two hidden layers with 6-5 nodes configuration. Trained ANN (4-6-5-2) predicted filtrate flux and filtrate volume with 2.33 and 1.38% mean relative error, respectively. The results suggest that the ANN modeling can be effectively used to optimize filtration process.

PRACTICAL APPLICATION

Membrane separation processes including ultrafiltration have gained importance in the food industry. Today, fruit juices are widely clarified by means of ultrafiltration process instead of tedious and laborious conventional clarification treatments. Membrane fouling which results in flux decline is the main problem associated with the ultrafiltration of fruit juices. In order to perform an efficient ultrafiltration process, optimization is required to obtain maximum filtrate volume per unit time. Artificial neural network (ANN) modeling offers great advantage on improving the performance of ultrafiltration process by accounting the effects of different variables, i.e., feed properties, transmembrane pressure and membrane pore size on filtrate volume as the main output of the filtration process. ANN modeling of ultrafiltration may be an alternative to previously proposed empirical and semiempirical models.     

A PRIORIESTIMATE FOR LOWER SOLUTIONS OF A CLASS QUASILINEAR ELLIPTIC EQUATIONS

考虑了拟线性椭圆型方程∫Ｇ｛ｖＡ（ｘ，ｕ，ｕ）＋ｖＢ（ｘ，ｕ，ｕ）｝ｄｘ＝０，ｖ∈Ｗ１ｐ（Ｇ）得到了此方程下解的先验估计，推广和改进了已有文献中的某些结果。     

MODELING THERMAL SOFTENING KINETICS OF POTATOES USING FRACTIONAL CONVERSION OF RHEOLOGICAL PARAMETERS

Texture degradation in potatoes was investigated during heating of cylindrical test samples, 15 mm diameter and 30 mm long, in water at 60, 70, 80 and 90C by mechanical testing. The rheological parameters obtained from the axial and radial compression, creep and stress relaxation tests decreased exponentially with an increase in heating duration and temperature approaching steady levels corresponding to the remaining texture after prolonged heating. A single first-order kinetic model described the changes in various rheological parameters due to thermal softening of potatoes using fractional conversion technique indicating very high values of the coefficient of determination (R² > 0.97). In general, the visco-elastic test parameters were relatively more sensitive to texture degradation in potatoes in comparison with the quasi-static test parameters. Overall comparison showed that elasticity and viscosity parameters in Kelvin component of the 4-element model (E₂ and η₂) from creep tests and elasticity moduli from axial and radial compression tests (E_a and E_r) best presented the texture degradation kinetics in potatoes with R² ranging from 0.98 to 0.99.     

RHEOLOGICAL MODELING OF UHT MILK GELS USING A CONE AND PLATE CREEP-RELAXATION TEST1

The gelation of UHT steam injected dairy products was investigated by determining rheological model constants. Fat percentages of the products were 0.5, 3.25 and 10.5. Each product was processed at 143 °C for 6.9 s and stored at 24 °C. At four week intervals, from 55 to 85 weeks storage, cone and plate creep-relaxation data was collected Three element rheological models were developed for each test date. Empirical relationships were derived relating the elastic and viscous constants to storage time for each fat content. The strongest parameter for all samples was the series elastic constant. The viscous constant was next with the Kelvin elastic constant being much weaker. All constants for all samples increased over storage time as gelling progressed (apparent viscosity increased). The lower the percent fat, the sooner gelling started and the faster the rate. The gelation of UHT milk was examined and found to depend heavily on the percent fat.