Observations of casein micelles in skim milk concentrate by transmission electron microscopy

Karlsson, Anders Ola; Ipsen, Richard; Ardö, Ylva

doi:10.1016/j.lwt.2006.05.012

Cited by 43 publications

(34 citation statements)

References 14 publications

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“…The results of Martin et al (2010), obtained by PCS methods, were consistent with those obtained through TEM by Karlsson et al (2007) using three different sample preparation steps. Both studies were also consistent with (McKenna, 2000), who utilized electron microscopy and reported no change in casein micelle size distribution under conditions of UF.…”

Section: The Effect Of Uf and Df On Casein Micelle Size Distributionssupporting

confidence: 80%

“…Some studies reported that casein micelle size appeared to be unchanged, while others reported increased or decreased sizes. Karlsson et al (2007) reported no observable changes in casein micelle size when UF retentate was observed under TEM, using three different preparation techniques, though it was must be noted that any TEM preparation (and virtually any microscopy preparation) may itself interfere with sample size. Singh (2007), utilizing electron microscopy, reported an increase in micelle size during the course of UF.…”

Section: The Effect Of Uf and Df On Casein Micelle Size Distributionsmentioning

confidence: 94%

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Effect of sodium chloride addition during diafiltration on the solubility of milk protein concentrate

Gualco¹

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There is considerable interest among food manufacturers to incorporate protein into food products in both developed and developing countries. Dairy proteins are excellent choices for many different applications, as they are known to have several nutritional and functional benefits. Membrane filtration techniques are often utilized as the preferred method of fractionation, due to the high throughput and continuous nature of the process. One such product produced from membrane filtration of skim milk is called milk protein concentrate. This product is valued for its high protein content, but it has historically exhibited poor solubility when reconstituted into water, which severely restricts the food applications for which it is suitable. There is some existing evidence that milk protein concentrates which contain elevated levels of sodium exhibit higher solubility upon reconstitution into water. The main objective of this thesis project was to demonstrate the effect of sodium chloride, added to diafiltration water utilized during the manufacturing process, on the solubility of milk protein concentrate.It was observed that the addition of sodium chloride into diafiltration water at levels of 50 mM, 100 mM, and 150 mM had a beneficial effect on the solubility of milk protein concentrate across a variety of reconstitution conditions. For example, when milk protein concentrate was mixed for 1 h on a stage mixer at 23 °C ± 1 °C, a significant increase (p < 0.001) in mean solubility was observed when at least 50 mM NaCl had been incorporated into DF water. The incorporation of 50 mM NaCl into DF water v significantly increased (p < 0.001) the mean solubility of milk protein concentrate from 59.81 % to between 64.34 % and 71.78 %. The addition of 100 mM NaCl significantly increased (p < 0.001) the solubility to between 88.80 % and 96.24 %, and the addition of 150 mM NaCl significantly increased (p = 0.005) the solubility to between 92.79 % and 100 %.Minerals analysis of dry powders revealed a significant increase (p < 0.001) in levels of sodium. The addition of 50 mM NaCl into DF water was associated with a significant increase (p < 0.001) in powder Na content to between 2.48 mg/g and 7.44 mg/g. The addition of 100 mM NaCl into DF water was associated with a significant increase (p = 0.002) in powder Na content to between 5.80 mg /g and 10.75 mg/g, and the addition of 150 mM NaCl into DF water was associated with a significant increase (p = 0.001) in powder Na content to between 9.57 mg/g and 14.53 mg/g. A significant difference (p < 0.001) in magnesium level was also detected. Differences in calcium content were not found to be statistically significant (p = 0.016) at α = 0.01.Preliminary observations of milk protein concentrate upon reconstitution were made using a confocal laser scanning microscopy method. This method showed evidence of possible differences in powder particle rehydration and affinity for lipid association between powder particles manufactured at different treatment levels. As the level of NaCl incorp...

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Section: The Effect Of Uf and Df On Casein Micelle Size Distributionssupporting

confidence: 80%

Section: The Effect Of Uf and Df On Casein Micelle Size Distributionsmentioning

confidence: 94%

Effect of sodium chloride addition during diafiltration on the solubility of milk protein concentrate

Gualco¹

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“…The very minor differences (<3 nm) in the measured micelle size of the three samples were not significant relative to the uncertainty of the measurements. Results of previous studies have been inconsistent with each other, with the size of casein micelles reported to be unchanged (Karlsson, Ipsen, & Ardö , 2007), increased (Singh, 2007;Srilaorkul, Ozimek, Ooraikul, Hadziyev, & Wolfe, 1991) or decreased (Erdem, 2006) as a result of UF. The results presented here indicate that no major change in the micelle size occurred during ultrafiltration/diafiltration or evaporation.…”

Section: Effect Of Mpc Manufacture On Casein Micelle Sizementioning

confidence: 69%

Effect of manufacture and reconstitution of milk protein concentrate powder on the size and rennet gelation behaviour of casein micelles

Martin

Williams

Dunstan

2010

International Dairy Journal

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“…[13][14][15][16] Addition of NaCl generally increases hydration, voluminosity, screening of charges of caseins and calcium ion activity in the milk serum whereas it decreases pH and the amount of supernatant casein, 17,18 improves rehydration of casein micellar powder, 19 imparts changes in casein micellar structure and micellar mineral composition. [20][21][22] In earlier investigations, various but limited techniques have been employed to study the effect of NaCl on the structural properties of casein micelles or milk systems including transmission electron microscopy (TEM) [23][24][25] , scanning electron microscopy (SEM) 26 and dynamic light scattering (DLS). 27,28 Several methods with their certain merits have been used for the analysis of proteins structure.…”

Section: Introductionmentioning

confidence: 99%

Multiscale Characterization of Casein Micelles Under NaCl Range Conditions

et al. 2011

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Micellar casein (MC) dispersions were studied at a constant protein concentration of 5 wt % in high NaCl environment. The micellar edifices were characterized as to their morphology, size, and content of proteins in the supernatant after ultracentrifugation. Additionally, changes in secondary structures of the protein upon salt increase were followed by Fourier Transform Infrared Spectroscopy (FTIR). For the first time, the estimations of secondary structural elements (irregular, ß-sheet, α-helix and turn) from Amide III assignments were correlated with results from Amide I. Casein micelles dispersions in water were characterized by Transmission Electron Microscopy (TEM) by a spherical shape and a size between 100 and 200 nm. A salt increase resulted to a destabilization of the micelle and the formation of mini-micelles more or less aggregated. The size of the new edifice was almost similar to the native micelle. These TEM observations were confirmed by a constant casein micelle hydrodynamic diameter determined by Dynamic Light Scattering (DLS) and ranging between 150 and 180 nm. Upon salt increase, FTIR revealed an increase in irregular structures and a concurrent decrease in ß-sheet structures. Secondary structural elements percentages were almost similar from Amide I and Amide III. The use of these multiscale techniques led to a better understanding of the micellar edifice under high salt environment. Around 3% NaCl addition, a good correlation was observed between destabilization of the micellar edifice, modifications of the caseins secondary structure and repartition of caseins between supernatant and pellet after ultracentrifugation.

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Observations of casein micelles in skim milk concentrate by transmission electron microscopy

Cited by 43 publications

References 14 publications

Effect of sodium chloride addition during diafiltration on the solubility of milk protein concentrate

Effect of sodium chloride addition during diafiltration on the solubility of milk protein concentrate

Effect of manufacture and reconstitution of milk protein concentrate powder on the size and rennet gelation behaviour of casein micelles

Multiscale Characterization of Casein Micelles Under NaCl Range Conditions

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