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Harjinder Singh - One of the best experts on this subject based on the ideXlab platform.
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changes in the surface protein of the fat globules during homogenization and heat treatment of Concentrated Milk
Journal of Dairy Research, 2008Co-Authors: Skelte G Anema, Harjinder SinghAbstract:The changes in Milk fat globules and fat globule surface proteins of both low-preheated and high-preheated Concentrated Milks, which were homogenized at low or high pressure, were examined. The average fat globule size decreased with increasing homogenization pressure. The total surface protein (mg m-2) of Concentrated Milk increased after homogenization, the extent of the increase being dependent on the temperature and the pressure of homogenization, as well as on the preheat treatment. The concentrates obtained from high-preheated Milks had higher surface protein concentration than the concentrates obtained from low-preheated Milks after homogenization. Concentrated Milks heat treated at 79 degrees C either before or after homogenization had greater amounts of fat globule surface protein than Concentrated Milks heat treated at 50 or 65 degrees C. This was attributed to the association of whey protein with the native MFGM (Milk fat globule membrane) proteins and the adsorbed skim Milk proteins. Also, at the same homogenization temperature and pressure, the amount of whey protein on the fat globule surface of the Concentrated Milk that was heated after homogenization was greater than that of the Concentrated Milk that was heated before homogenization. The amounts of the major native MFGM proteins did not change during homogenization, indicating that the skim Milk proteins did not displace the native MFGM proteins but adsorbed on to the newly formed surface.
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Rheological properties of Concentrated skim Milk: importance of soluble minerals in the changes in viscosity during storage.
Journal of dairy science, 2003Co-Authors: Annie Bienvenue, Rafael Jiménez-flores, Harjinder SinghAbstract:Properties of condensed Milks prior to spray drying dictate to a large extent the functionality of the resulting Milk powder. Rheological properties of Concentrated skim Milk, with total solids content of 45% but different mineral content, were studied as a function of shear rate and storage time at 50 degrees C. These Milks are proposed as a model to study the effects of minerals on rheology and age gellation of condensed Milk prior to drying. During storage of the Concentrated Milk, the apparent viscosity, particularly after 4 h, increased markedly at all shear rates studied. The yield stress also increased steeply after 4 h of storage at 50 degrees C. The changes in apparent viscosity of Concentrated Milk stored for up to 4 h were largely reversible under high shear, but irreversible in samples stored for longer time. The appearance of yield stress suggested the presence of reversible flocculation arising from weak attraction between casein micelles, with a transition from reversible to irreversible aggregation during storage. Particle size analysis confirmed irreversible aggregation and fusion of casein micelles during storage. Gradual reduction of mineral content of Concentrated Milks resulted in a marked decrease in the apparent viscosity and casein micelle aggregation during storage, while addition of minerals to Milk had the opposite effect. The results demonstrated that the soluble mineral content is very important in controlling the storage-induced changes in the rheology of Concentrated Milks.
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rennet coagulation properties of skim Milk Concentrated by ultrafiltration effects of heat treatment and ph adjustment
Food Research International, 1998Co-Authors: Algane Waungana, Harjinder Singh, Rodney J BennettAbstract:Abstract Skim Milks were ultrafiltered to produce concentrates with protein levels of ∼6 and ∼9%, and were then heated at 140°C for 4 s in a UHT plate heat exchanger. In some cases, skim Milks were heated at 140°C for 4 s prior to ultrafiltration. Rennet coagulation properties were assessed using low amplitude oscillatory rheometry by measurements of storage modulus (G′) as a function of time after rennet addition. Concentration of skim Milk by UF had no effect on gelation time (GT) when measurements were made at the natural pH. However, when measurements were made at pH 6.5, concentration of Milk resulted in a decrease in GT. Curd firming rates and the final G′ values increased with increase in Milk concentration by UF. UHT-treatment of UF Concentrated Milk resulted in increased GT, decreased curd firming rates and decreased G′ values; the effects of heat treatment on these properties were greater when UHT treatment was given to skim Milk prior to UF. Acidification of UHT-treated skim Milk and UF concentrates to pH 5.5, followed by neutralization to pH 6.5 (‘pH cycling’), resulted in an improvement of rennet coagulation properties of normal Milk, but had no effect on 2X Concentrated Milk. In contrast, the rennet coagulation properties of 3X Concentrated Milks were adversely affected by pH cycling. Similar trends were noted when pH cycling was carried out on heated skim Milk prior to UF. ©
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Cross-linking of Milk proteins on heating Concentrated Milk at 120°C
International Dairy Journal, 1994Co-Authors: Harjinder SinghAbstract:Abstract Gel permeation chromatography on a column of TSK-GEL G4000SW in 6M urea was used to study the size distribution of protein aggregates in reconstituted heated Concentrated Milks and the corresponding colloidal calcium phosphate (CCP)-free Milks. The proportions of high molecular weight protein aggregates increased at the expense of intermediate-sized protein aggregates (cross-linked by CCP) and the monomeric protein with increase in heating time at 120°C. Examination of CCP-free Milks prepared from heated Concentrated skim Milks revealed that the quantities of protein aggregates not dissociated by the acidification/dialysis procedure increased with the severity of heating. SDS-electrophoresis showed that larger protein aggregates formed on heating were composed of α s - and β-caseins and an unidentified protein. It appeared that a new ‘slow-to-dissociate’ CCP was generated during heating of Concentrated Milk and this new calcium phosphate was possibly involved in the formation of larger-sized protein aggregates. It is likely that these aggregates are involved in the association of casein micelles during heating.
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In vitro Digestibility of Whey Protein/K‐Casein Complexes Isolated from Heated Concentrated Milk
Journal of Food Science, 1993Co-Authors: Harjinder Singh, Lawrence K. CreamerAbstract:The disulfide-linked complex of K-casein and whey proteins that forms when Concentrated Milk is heated was isolated by centrifugation and column chromatography on Sephacryl S-1000. The rate of hydrolysis of β-lactoglobulin and K-casein in the complex and the reduced and carboxymethylated components of the complex were measured by polyacrylamide gel electrophoresis. The rates of hydrolysis at pH 2.0 (pepsin) and pH 8.0 (trypsin and chymotrypsin) were similar for k-casein in the complex and its reduced form. β-Lactoglobulin hydrolysis was faster for the reduced complex than for the complex which was much faster than for the native protein for all three enzymes. The results suggest that heating Milk increases the digestibility of whey proteins, despite the formation of large protein complexes between the whey proteins and K-casein.
Milena Corredig - One of the best experts on this subject based on the ideXlab platform.
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Changes in the physico-chemical properties of casein micelles in the presence of sodium chloride in untreated and Concentrated Milk protein
Dairy Science & Technology, 2015Co-Authors: Zhengtao Zhao, Milena CorredigAbstract:The addition of NaCl to Milk is known to alter the mineral equilibrium and the structure of casein micelles. The objective of this study was to better understand the light scattering properties and viscosity of Milk as a function of NaCl addition (0–500 mmol.L^−1), for fresh skim Milk and 2× Concentrated Milk protein. Suspensions (2×) were prepared using osmotic stressing. NaCl was added by dialyzing Milk with Milk serum (permeate) for 18 h. The presence of NaCl decreased the pH of Milk and the zeta potential of casein micelles. When measured under diluted conditions, using dynamic light scattering, the average radius of the casein micelles showed a small increase, from 84 to 88 nm. Total calcium and phosphate in Concentrated Milk protein suspensions decreased with NaCl concentration, with a corresponding increase of the permeable calcium and phosphate, and of non-sedimentable caseins. In both untreated and Concentrated Milk protein samples, the viscosity increased with NaCl concentration. The characteristic decay time (τ) and turbidity measured under non-diluted conditions using diffusing wave spectroscopy showed a gradual decrease with NaCl addition. This work demonstrated that the changes to Milk with addition of NaCl are mainly caused by the disruption of the internal structure of the casein micelles and changes in the composition of the serum phase, affecting the viscosity of the continuous phase as well as the refractive index contrast.
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Physico-chemical properties of casein micelles in unheated skim Milk Concentrated by osmotic stressing: Interactions and changes in the composition of the serum phase
Food Hydrocolloids, 2014Co-Authors: Pulari Krishnankutty Nair, Marcela Alexander, Douglas G. Dalgleish, Milena CorredigAbstract:Abstract The changes in processing functionality of Concentrated Milk are caused by a number of factors, amongst the most important, the ionic equilibrium and the increase in the interactions between the casein micelles because of their increased volume fraction. The objective of this work was to characterize the physico-chemical properties of casein micelles as a function of their volume fraction, by using osmotic stressing as a non-invasive method to obtain Concentrated Milk, in the attempt to preserve the ionic balance during concentration. Osmotic concentration was carried out for 18 h at 4 °C, using different concentrations of polyethylene glycol dissolved in permeate as the stressing polymer. The viscosity of the Concentrated Milk could be predicted using established rheological models, when the changes occurring to the viscosity of the serum phase were taken into account. Both Eilers and Mendoza equations predicted a maximum packing volume fraction of 0.8 for the casein micelles. After concentration up to 20% protein, the casein micelles did not show a change in their size upon redilution. Light scattering measurements carried out using diffusing wave spectroscopy without dilution suggested that casein micelles behave as hard spheres with the characteristic of free diffusing Brownian particles up to a volume fraction of 0.3, and restricted motion at higher concentrations. Results of total and soluble calcium suggested release of colloidal calcium phosphate from the micelles at volume fractions >0.35. This research brings new insights on the changes occurring in skim Milk during concentration.
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on line diffusing wave spectroscopy during rheological measurements a new instrumental setup to measure colloidal instability and structure formation in situ
Food Research International, 2013Co-Authors: Marcela Alexander, Milena CorredigAbstract:Abstract A novel setup was employed to investigate the destabilization of colloids, using a rheometer in line with diffusing wave spectroscopy (DWS) in backscattering mode. The newly designed system consists of a concentric cylinder couette geometry fitted with a window to perform simultaneous light scattering measurements. To test the ability of this Rheo-DWS setup to follow the dynamics of destabilization of model systems such as skim Milk and emulsions, parallel experiments were also carried out using a separate transmission DWS equipment. For skim Milk, containing 10% of volume of protein particles (casein micelles) of about 200 nm in diameter, the physical constraints imposed by the rheological setup did not allow calculation of the correct value of the diffusion coefficient, as the diffusion approximation could not be fulfilled. On the other hand, for Concentrated Milk (4 × the original volume fraction) and for oil in water emulsions, the characteristic decay constant, τ, yielded correct size values calculated using known DWS theory. The ability to follow the dynamics of early gelation using Rheo-DWS was tested by measuring the changes occurring during gelation of skim Milk, Concentrated Milk and emulsions. There were no statistically significant differences between the gelation times measured in situ using backscattering DWS and transmission DWS. The data obtained by light scattering were in full agreement with rheology experiments. The results demonstrate the potential of such setup to follow the dynamics of colloidal destabilization and structure formation in situ while subjecting them to simultaneous rheological measurements.
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Colloidal properties of Concentrated heated Milk
Soft Matter, 2013Co-Authors: Pulari Krishnankutty Nair, Douglas G. Dalgleish, Milena CorredigAbstract:The colloidal properties of casein micelles in heated Milk as a function of volume fraction are largely unknown. Heat-treatment of Milk causes denaturation and unfolding of whey proteins, which then react with caseins to form a complex mixture of soluble whey protein aggregates and whey protein coated casein micelles. The distribution of the complexes between the soluble and the micellar phase depends on the pH of Milk before heating. This work focused on the contribution of the heat induced complexes to the colloidal properties of Concentrated casein micelles. Concentration was performed using osmotic stressing. Although there were differences in the apparent diameter after heating Milk at pH 6.4, 6.8 or 7.0, redilution of the Concentrated Milk showed no irreversible aggregation of the casein micelles with concentration. Above 70 g L−1 protein, there was a decrease in the mean square displacement slope measured by light scattering, suggesting that above this concentration, the casein micelles were no longer free diffusing. The viscosity of the Concentrated Milk could be predicted using a rheological model for hard spheres assuming constant voluminosity.
Gustavo V. Barbosa-cánovas - One of the best experts on this subject based on the ideXlab platform.
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FLOW AND STRUCTURAL CHARACTERISTICS OF Concentrated Milk
Journal of Texture Studies, 2000Co-Authors: Jorge F. Vélez-ruiz, Gustavo V. Barbosa-cánovasAbstract: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.
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Flow and viscoelastic properties of Concentrated Milk treated by high hydrostatic pressure
Lwt - Food Science and Technology, 1998Co-Authors: J F Vélez-ruiz, Barry G. Swanson, Gustavo V. Barbosa-cánovasAbstract:Abstract The present study analysed the effects of high isobaric pressure on the rheological and structural characteristics of Concentrated Milk. Milk concentrates receiving high hydrostatic pressure (HHP) treatment in the range of 276–690 MPa were studied. Apparent viscosity and storage modulus quantitatively reflected the influence of the applied high pressure treatment, and the pressure-induced gelation of Milk concentrates led to the formation of a fine network that exhibited both viscous and elastic properties. The rheological behavior of Milk concentrates was characterized as a function of solids content (129 to 471 g/kg) and HHP treatment. Steady and dynamic shear were applied to follow the rheological response of Concentrated Milk prior to and after the HHP process. The Milk concentrates' consistency expressed by the apparent viscosity as a function of the concentration level was fitted by a single-term exponential model ( ln μ a = A + bX ), whereas as a function of the concentration and pressure it was modeled by a two-term logarithmic equation ( ln μ a = β 0 + β 1 X + β 2 P ). The storage modulus, which reflected the effect of both variables very well, was plotted as a function of the shear frequency. Based on the rheological results exhibited by the Milk concentrates subjected to 414 MPa, this treatment was selected as the most convenient pressure for further analyses. Scanning electronic microscopy allowed observation of the structural changes of Concentrated Milk due to the HHP and the differences among pressure treatments. HHP led to the disintegration of the native protein of Milk concentrates, producing a gel of relatively uniform structure. Changes detected in viscosity, viscoelasticity and texture for Concentrated Milk could be attributed to the HHP process, which mainly affected the protein structure.
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Rheological properties of Concentrated Milk as a function of concentration, temperature and storage time
Journal of Food Engineering, 1998Co-Authors: Jorge F. Vélez-ruiz, Gustavo V. Barbosa-cánovasAbstract:The flow properties of Concentrated Milk were evaluated between concentrations of 12.6 and 48.6% solids content, at three temperatures and through 4 weeks of storage. Three rheological models, Newton, power law and Herschel-Bulkley, were applied to fit the flow behavior of Milk concentrates depending on the concentration level. The resulting flow behavior indices and consistency coefficients were correlated to concentration by a single term exponential equations, with only two concentrates, 42.4 and 48.6% solids contents exhibiting yield stress. The effect of the temperatures studied on the flow behavior index was minimal, though noticeable on the consistency coefficient, and at the three selected temperatures (5, 15 and 25 °C) the flow behavior index decreased with storage time while the consistency coefficient increased. The energy of activation for flow (evaluated with an Arrhenius type equation) increased with concentration and storage time and ranged from 2.42 to 11.8 kcal gmol−1. A nonlinear model accounting for temperature and concentration effects on the consistency coefficient was identified. The constants of the aforementioned nonlinear model were different for each week of storage. During the 4 weeks of storage the consistency coefficient showed no significant differences, in contrast to the flow behavior index.
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Effects of concentration and temperature on the rheology of Concentrated Milk
Transactions of the ASAE, 1997Co-Authors: Jorge F. Vélez-ruiz, Gustavo V. Barbosa-cánovasAbstract:The flow properties of Milk concentrates covering a solid content range of 12.7% to 40.4% made from fresh whole Milk were determined with a double concentric cylinder geometry in a rotational rheometer. Shear stress or apparent viscosity corresponding to a 500 to 1000 s–1 shear rate range were recorded; and from these shear rate-shear stress data the flow nature of Milk concentrates was evaluated. The rheological behavior of Milk concentrates was represented by parameters corresponding to Newton, Power Law, or Herschel-Bulkley equations, depending on the solid content level. The flow behavior index (n) and the consistency coefficient (K) were exponentially correlated to Milk concentration. The consistency coefficient followed the Arrhenius temperature relationship and the activation energy for the concentrates ranged from 4.3 to 6.1 kcal/gmole. These two rheological parameters (n and K) significantly changed with concentration and temperature. The consistency coefficient was correlated to concentration and absolute temperature by a simple mathematical relationship, which is useful for equipment and process design.
Yves Pouliot - One of the best experts on this subject based on the ideXlab platform.
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Observations on the seasonal variations in the salt balance of Concentrated Milk
International Dairy Journal, 1995Co-Authors: Yves Pouliot, M. BouletAbstract:Abstract Seasonal variations in the salt balance of raw bulk Milk and its 3:1 concentrate were studied over a one-year period. A marked increase in the level of colloidal calcium was found between December and February in raw Milk, whereas the other components remained unchanged. Evaporative concentration shifted the soluble-colloidal equilibrium towards the colloidal phase as the Ca, PO4, Mg and citrate content increased. Thermal stabilization of the concentrates by pH adjustment or Na2HPO4 addition had little effect on salt balance at any time of the year. The colloidal Ca PO 4 ratio was the only compositional parameter that could be correlated to the heat stability of Concentrated Milk.
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Seasonal Variations in the Heat Stability of Concentrated Milk: Effect of Added Phosphates and pH Adjustment
Journal of Dairy Science, 1991Co-Authors: Yves Pouliot, Marylène BouletAbstract:Abstract Natural variations in heat stability of 31% total solids Concentrated Milk have been surveyed over a 1-yr period. Very small variations occurred, and no distinctive instability period was observed. The stabilizing effect of pH adjustment with NaH 2 PO 4 ·Na 2 HPO 4 or NaOH·HC1 before sterilization was studied. The phosphates produced better stabilization than the acid-base combination at any pH between 6.0 and 7.0. The effectiveness of Na 2 HPO 4 showed seasonal variations: the effects were marked on summer Milks and smaller in winter Milks. Conversely, seasonal variations were observed in the buffer capacity of the concentrates. The results emphasize the possibility of a specific stabilization mechanism by phosphate salts on Concentrated Milks.
Arthur R. Hill - One of the best experts on this subject based on the ideXlab platform.
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TEXTURE ANALYSIS OF CHEDDAR CHEESE MADE FROM ULTRAFILTERED Milk
Journal of Food Quality, 1991Co-Authors: Sujata Lakhani, E. A. Gullett, L.k. Ferrier, Arthur R. HillAbstract:The textural properties of Cheddar cheese made from ultrafiltered Milk were assessed. Cheddar cheeses were prepared from 1.5- and 2.0-fold Concentrated Milk and ripened for three months. Textural characteristics of the UF cheeses were compared to control and commercial Cheddar cheeses by sensory and instrumental measures. The texture of cheese made from UF Milk differed from the control commercial Cheddar cheeses. According to the trained sensory panel, the UF cheeses were harder and more rubbery, crumbly, chewy and grainy than the control and commercial Cheddar cheeses (P