乳清蛋白质浓缩物的流变学性质

本研究以3种工业化生产的乳清蛋白浓缩物(WPC)的再制溶液为对象,测定其不同条件下的流动特性,即在剪切速率3～1321/sec、温度5～65℃、总固形物浓度5～40％,pH3～10等条件下,溶液的剪切应力与剪切速率和剪切应力与剪切时间的关系。WPC溶液的流变学行为与溶液的浓度、温度、pH有关。在多数实验条件下,WPC溶液具有假塑性液体性质,可以用幂律模式(power law module)来表示,在极端条件下,溶液的流动特性则接近牛顿液体或塑性液体。     

Effects of temperature,shear rate and constituents on rheological properties of tahin (sesame paste)

In this paper, rheological properties of tahin are reported at temperatures from 20 to 70 °C and shear rates in the range 0.13–500 s^?1. Temporary hysteresis loops were observed in the first cycle of the flow curves. The steady shear behaviour of tahin was pseudoplastic and described by a power law model. The consistency coefficient exhibited strong temperature dependence for which the activation energy of flow was 21.6 kJ mol^?1. The flow behaviour index of tahin tended to increase whereas the consistency coefficient tended to decrease during storage at room temperature. Tahin oil exhibited Newtonian behaviour with a strong dependence of viscosity on temperature. The activation energy of flow for tahin oil was 35.7 kJ mol^?1. While reconstituted suspensions containing up to 20% solids exhibited Newtonian behaviour, those with more solids and the original tahin showed pseudoplastic behaviour. The Krieger–Dougherty model fitted the suspension viscosity data well. Below 20% solids level there was no effect of particle size on the viscosity of the reconstituted suspensions. It was shown that for the same amount of solids the viscosity of a ‘polydisperse’ suspension was lower than that of a ‘monodisperse’ suspension. Copyright © 2004 Society of Chemical Industry     

RHEOLOGICAL BEHAVIOUR OF KIWI FRUIT JUICE CONCENTRATES

The rheological behaviour of diluted kiwi concentrates (22.5–63.0 °Brix) over the temperature range 4 to 70C, was studied. The values below 55.7 °Brix fit the power law while above 55.7 °Brix fit the Herschel-Bulkley equation. Maximum and minimum consistency index values were 62225 and 16 mPa. s ⁿ . Concentrates showed a yield stress at 55.7 °Brix, from 5 to 11 Pa, and 63.0 °Brix, from 19 to 53 Pa. Yield stress was correlated with temperature by means of a linear equation. Arrhenius activation energies were in the range of 28.97 to 33.89 kJ/mol. The average value of the flow behaviour indexes varied from 0.85 (sample at 22.5 °Brix) to 0.59 (sample at 63.0 °Brix). Simple equations are proposed to describe the combined effect of temperature and soluble solids content on consistency index and rheological behaviour index.     

Effect of processing and storage on rheological properties of fortified milk and curd systems

Fortified milk systems were prepared by blending pasteurized standardized milk with skim milk powder, peanut flour or peanut protein isolate to 15, 18, 20, and 23% total solids followed by processing at 60°C and 80°C for 30min and storage at 4°C for 24h. Curds were prepared by the lactic fermentation of the processed milk systems. The rheological properties showed that all the systems exhibited pseudoplastic flow. The flow became less Newtonian with increasing total solids, heat treatment, and storage. Curd obtained from the fortified milk processed at 80°C showed increased yield stress and curd strength with the increasing concentration. Degree of heat treatment, total solids content and storage were shown to have a pronounced effect on the apparent viscosity, consistency index, and yield stress of the fortified milk systems.     

COAGULATION OF FISH PROTEINS FROM FROZEN FISH MINCE WASH WATER BY OHMIC HEATING

A batch-type ohmic heating device was developed to investigate the possibility of coagulating fish proteins from frozen fish mince wash water. At constant voltage (90 VAC), the temperature of wash water samples was raised to different set points (40, 50, 60, 70, and 80C, respectively). Effect of heating on coagulation of proteins and removal of COD, TS, and TSS was investigated. When the temperature reached 70C, 33.0%, 59.3%, 33.3%, and 92.1% protein, COD, TS, and TSS, respectively, were removed from the wash water. Holding samples at constant temperatures for longer time periods did not improve solids removal, except at 40C. The highest heating temperature for effective coagulation of proteins and removal of solids is 70C. The relationship between heating temperature and heating time followed a second order polynomial model. Apparent electrical conductivity and energy consumption increased linearly with the heating temperature. At the early stage of heating, almost all electric energy was converted to heat energy. As the temperatures rose, energy efficiency began to decrease linearly with the temperature. Overall energy efficiency was above 86%.     

FLOW AND STRUCTURAL CHARACTERISTICS OF CONCENTRATED MILK

The flow and structural characteristics of concentrated milk were analyzed between concentrations of 12.5 and 46.7% solids content at room temperature. The rheological behavior of milk concentrates was represented by parameters corresponding to Newtonian, Power Law, or Herschel-Bulkley equations depending on the solids content level. The resulting flow behavior indices and consistency coefficients were correlated to concentration by a single-term exponential equation, with only milk concentrates above 40% solids content exhibiting yield stress. Milk concentrates were characterized by scanning electron microscopy (SEM), complemented by transmission electron microscopy (TEM) and image analysis (IA). Casein micelles appeared as granular particles (0.1–0.3 μm) with a rough surface. Fat globules, noted as small holes in the SEM pictures, appeared to be major spherical components (0.5–10 μm) in the transmission electron microscope images as well as in the image analysis inverted micrographs. Fat globules in the milk concentrates were surrounded by a membrane which was thicker in the concentrated milk than in the fresh milk. TEM images were very helpful in observing the interparticle interactions, as well as the thickness of the fat membranes that corroborated with the SEM observations. The IA pictures allowed the identification and characterization of the fat globule features.     

Rheology of raspberry juices

This paper reports a study of the rheological behaviour of different concentrations of raspberry juice at different temperatures. The behaviour is pseudoplastic at higher concentrations and lower temperatures, although at low concentrations and in some cases at high temperatures the behaviour is Newtonian.The effect of temperature and soluble solids content on the consistency coefficient was also studied: an equation was derived which describes the combined effect of these two variables for two different models and over the range of temperatures and concentrations studied.     

Evaluation of Yield and Quality of Cheddar Cheese Manufactured from Milk with Added Whey Protein Concentrate

Cheddar cheese was produced from whole milk with blends of whey protein concentrates added. Two whey protein concentrate powders containing 35 or 55% protein were each reconstituted to a 15% (wt/wt) suspension and heat treated at 70°C for 15 min. Addition of the denatured whey protein concentrate suspension to the milk was at 5 or 10% by weight of the milk. Addition of reconstituted partially denatured whey protein concentrate increased cheese yields from 1.4 to 6.2% above those of the control on a 63% solids basis. The only significant (P<.05) increase in yield was from the 55% whey protein concentrate suspension at 10% replacement by weight of the milk. The correlation coefficient between percent denaturation in the whey protein concentrate and yield in this cheese was .62. Experimental cheese had decreased fat and total solids contents and increased total nitrogen, ash, and salt. Fat reduction varied from 4.3 to 18.2% below the control cheese, and total solids were from 1.7 to 8.9% below the control cheeses. Total nitrogen values of experimental cheese were from .73 to 5.64% above the control. Cheeses were evaluated organoleptically; more flavor defects were associated with increased whey protein concentrate in the experimental cheese. The most common criticism of the experimental cheese was an atypical (unclean) cheese flavor.     

THE FLOW PROPERTIES OF SKIM MILK CONCENTRATES OBTAINED BY ULTRAFILTRATION

The flow properties of skim milk concentrates were measured at temperatures ranging between 5 and 60 °C. The concentrates obtained by ultrafiltration showed, in the studied range of shear rate 5 < D < 1000s^?1, pseudoplastic behaviour depending on solids content and temperature. This behaviour is well described by the power law. For both the parameter ψ and n of this law there is a clear dependence on solids content and temperature. The viscosity parameter ψ increases highly from a certain solid content. As there exists a relation between the viscosity and the coefficient of diffusion, which is an essential factor of influence on the process of ultraflltration, these well defined results of objective rheological measurements have consequences about the practicability of this process of separation for the enrichment of protein in skim milk.     

Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella in cranberry, lemon, and lime juice concentrates

The production of thermally concentrated fruit juices uses temperatures high enough to achieve at least a 5-log reduction of pathogenic bacteria that can occur in raw juice. However, the transportation and storage of concentrates at low temperatures prior to final packaging is a common practice in the juice industry and introduces a potential risk for postconcentration contamination with pathogenic bacteria. The present study was undertaken to evaluate the likelihood of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella surviving in cranberry, lemon, and lime juice concentrates at or above temperatures commonly used for transportation or storage of these concentrates. This study demonstrates that cranberry, lemon, and lime juice concentrates possess intrinsic antimicrobial properties that will eliminate these bacterial pathogens in the event of postconcentration recontamination. Bacterial inactivation was demonstrated under all conditions; at least 5-log Salmonella inactivation was consistently demonstrated at -23 degrees C (-10 degrees F), at least 5-log E. coli O157:H7 inactivation was consistently demonstrated at -11 degrees C (12 degrees F), and at least 5-log L. monocytogenes inactivation was consistently demonstrated at 0 degrees C (32 degrees F).     

Effects of Polymerized Whey Proteins on Consistency and Water-holding Properties of Goat's Milk Yogurt

ABSTRACT The effects of polymerized whey proteins (PWP) on functional properties of goat's milk yogurt were investigated. PWP were prepared by heating whey protein isolate (WPI) dispersion (8.0% protein, pH 7.0) at 90 °C for 30 min. Three reconstituted goat milk (RGM) (12% total solids [TS] as control; RGM with 2.4% unheated WPI; and RGM with 2.4% PWP) and 1 RGM with 16.7% TS were prepared and inoculated with 0.04% yogurt starter culture. Inoculated milk was incubated at 43 °C for 5 h, cooled to 4 °C in an ice‐water bath, and then placed at refrigerator (4 °C) overnight before testing. Incorporation of PWP significantly (P < 0.001) increased the viscosity (by 80%) and decreased the syneresis (by 25%) of the yogurt samples, whereas addition of unheated WPI did not significantly affect the viscosity and syneresis compared with the control. There were no changes in pH, TS, ash, fat, protein, and lactose contents among yogurt samples except the solids fortified control. Yogurt with 16.7% TS had the lowest syneresis but did not improve in viscosity. Transmission electron microscopy micrographs demonstrated that the microstructure of the goat's milk yogurt gel with PWP was denser than the control. Results of this study indicate that polymerized whey proteins may be a novel protein‐based thickening agent for improving the functional properties of goat's milk yogurt and other similar products.     

Rheological Modelling of the Effects of Sucrose Adulterant on Nigerian Honey

Rheology has been applied as sensitive tool for material characterisation since flow behaviour correlates closely with composition, molecular weight and molecular weight distribution. Pure honey was serially diluted with different percentages of sucrose: 10%, 50%, 70% and 90% and each were analysed rheologically at two different temperatures. Pure honey exhibits thixotropic time dependent rheological behaviour, while the behaviour of sucrose tends towards Newtonian. The addition of adulterant to honey drags the viscosity of the resulting fluid towards Newtonian. The rheological curve fitting was done using the Power Law and Carreau-Yasuda models. The results show that the Carreau-Yasuda model fitted better the rheology of pure honey samples. Conversely, the rheology of sucrose solution was predicted better with Power Law model.     

Viscometric Behavior of Reconstituted Tomato Concentrate

The rheological properties of tomato concentrates produced by hot and cold break have been extensively studied by many authors. Only a few studies, however, focus specifically with the rheology of reconstituted concentrates from tomato powders. In this study, the rheological properties of reconstituted tomato concentrate from lyophilized freeze-dried tomato juice were evaluated using rotational viscometer at temperatures 20 °C, 30 °C, 40 °C, 50 °C, and 60 °C and at concentrations of 9.7%, 12.9%, 20.5%, and 26.8% total soluble solids. Using power law model, both flow behavior index (n) and consistency coefficient (k) were determined. The calculated values of flow behavior index (n) were less than unity (0.03–0.28) at all temperatures and concentrations indicating the shear-thinning characteristic of the concentrate. The effect of temperature and concentration on the consistency coefficient (k) was studied. Positive correlation between k in the range of 1.57 and 38.33 Pa s ⁿ and inverse absolute temperature (1/T) has been shown by Arrhenius model. Additionally, linear correlation between consistency coefficient (k) and concentration (C) was determined. The activation energies were found in the range of 3.63 and 7.36 kJ/mol K depending on concentration. The results of this study might be useful to improve the design of processing operations dealing with tomato powder reconstitution.     

RHEOLOGICAL BEHAVIOUR OF CLARIFIED MANGO JUICE CONCENTRATES

The rheological behaviour of clarified mango juice was measured at temperatures 15–85C and concentrations 15–66 °Brix, using a rotoviscometer. Mango juice free of pectin and pulp behaves as a Newtonian fluid. The effect of temperature can be described by an Arrhenius-type equation. The activation energy for viscous flow was in the range of 1.64–8.44 kcal/g-mol, depending on the concentration. The effect of concentration was modelled better by an exponential relationship than a power-law relationship. Simple equations are proposed for describing the combined effect of temperature and soluble solids content on the juice viscosity.     

The rheology of starch dispersions at high temperatures and high shear rates: a review

Engineering design of continuous processes for liquid and semi-liquid foods involves a complex heat transfer and fluid flow coupling, which strongly depends on the rheological behaviour of fluid foods. Most of these processes are performed at temperatures above 95°C. Lack of rheological data is one major problem encountered during numerical simulation and equipment design of liquid food processing at high temperatures. Insufficient rheological studies in the literature have been conducted with food products under these conditions. This paper presents a literature review of experimental devices and methods used to obtain rheological data for starch dispersions at temperatures below and above 95°C. Results and gelatinization models from the literature are analysed and discussed.     

Determination of alpha-gliadin content in gluten-containing and gluten-free heated food

The amount of alpha-gliadin and whole gliadin in bread dough after heating at temperatures of 50-100 degrees C was determined by ELISA. At temperatures above 80 degrees C the amount which could be found was greatly reduced. In pasta foods containing wheat (with a max. drying temperature of 75 degrees C) alpha-gliadin could be determined totally but in wheat bread (crust and crumb) only 0.5-40% of the content in the original flour was found. The results of an analysis of "gluten-free" pasta foods on the market and the amounts of alpha-gliadin found are discussed in relation to the recommendations of the Codex alimentarius (WHO).     

Thermal and dynamic rheological properties of wheat flour fractions

A commercial high gluten flour (HGF) was fractionated into prime starch (PS), tailing starch (TS), and gluten (G). Fractions were examined alone or in various combinations. Dynamic rheological properties of samples were measured in an oscillatory rheometer (strain 0.02; frequency 0.1 Hz) during heating at 1°C/min. Thermal characteristics of samples were determined by differential scanning calorimetry (DSC) at a heating rate of 10°C/min. The loss (G″) and storage (G′) moduli of PS and mixed G/PS, G/TS, and G/PS/TS increased after 60°C, reaching peak values (e.g. 81, 301, 313, and 3000 Pa in G′, respectively) around 75°C after which the moduli decreased. HGF showed a steady increase in G′ from 32 to 2490 Pa as temperature increased from 65 to 90°C, indicating continuous formation of elastic networks. Cooling increased G′ for G/PS/TS, decreased G′ for HGF, and produced no rheological transitions for all samples. TS and G alone did not exhibit appreciable viscoelastic responses to the heating and cooling temperatures. DSC measurements revealed a major endothermic transition in HGF. This transition, with a peak around 60°C, was due to starch gelatinization. The presence of G or TS resulted in reduced melting enthalpies of starch in the PS fraction. Gluten or TS fractions alone or in combination did not exhibit any endothermic transitions.     

温度和TS对小麦酒糟厌氧发酵产气性能的影响

在温度为30℃、35℃、40℃、45℃、50℃,TS分别为6%、8%和10%的条件下,研究了小麦酒糟厌氧发酵过程中的pH值变化和气产率。结果表明,各实验条件下,发酵液pH值均呈现出先下降后升高的趋势,基质浓度通过改变反应混合物的pH值来间接影响发酵的反应过程,同一温度下,TS越高越容易出现酸化;不同温度下,TS对产气率的影响较大,温度40℃时的产气率远高于其他温度,且不同TS浓度下的产气率相差较大。在本实验条件下,温度为40℃、TS为6%是小麦酒糟厌氧发酵的最适宜条件。     

Effect of diacetyl on the heat stability of concentrated milks

Very low levels of diacetyl (1–5 mM) markedly increased the heat stability of concentrated milks (20% total solids) reconstituted from skim milk powders. Diacetyl caused only slight stabilization of the concentrates (following dilution to 20% total solids) used in the manufacture of these powders but its efficacy was increased by heating the concentrates (70°C for 10 min) prior to diacetyl addition and especially by freeze drying. Laboratory concentrated milks were destabilized by diacetyl and these samples were also destabilized by freeze drying. However, addition of diacetyl prior to preheating and concentration increased stability.     

Use of soybean isolate in coated foods: simulation study employing glass balls and substantiation with extruded products

Simulation studies on coating using glass balls as ideal solid and soy flour isolate dispersions of different concentrations (10–25%) and at different temperatures (20–50 °C) were conducted. A few coating parameters such as total uptake of dispersion, solid uptake, dimensionless uptake (DU) and uptake per unit area were determined. Further, the study was extended by using corn‐soy extrudates in place of glass balls while using soy flour isolate dispersion of same concentrations and maintained temperature ranges. Rheological characteristics of the dispersions like flow behaviour index, consistency index, apparent viscosity and yield stress were determined to relate them with coating behaviour. The dispersions behaved like a non‐Newtonian shear‐thinning fluid and exhibited yield stress between 0.75 and 1.72 Pa. An increase in concentration of solids in the dispersion increased yield stress, consistency index and apparent viscosity while the flow behaviour index decreased from 0.67 and 0.39. Inter‐relationships between various rheological and coating characteristics were determined; simulation studies on coating by employing glass balls can provide a good interrelation of |r| ≥ 0.88–0.99 that is comparable with |r| ≥ 0.69–0.99 (P ≤ 0.01) obtained with actual experimentation using corn‐soy extrudates.