Association of denatured whey proteins with casein micelles in heated reconstituted skim milk and its effect on casein micelle size

Food Science Section, Fonterra Research Centre (formerly NZDRI Ltd.), Private Bag 11029, Palmerston North, New Zealand.
J Dairy Res (Impact Factor: 1.39). 03/2003; 70(1):73-83. DOI: 10.1017/S0022029902005903
Source: PubMed

ABSTRACT When skim milk at pH 6.55 was heated (75 to 100 degrees C for up to 60 min), the casein micelle size, as monitored by photon correlation spectroscopy, was found to increase during the initial stages of heating and tended to plateau on prolonged heating. At any particular temperature, the casein micelle size increased with longer holding times, and, at any particular holding time, the casein micelle size increased with increasing temperature. The maximum increase in casein micelle size was about 30-35 nm. The changes in casein micelle size were poorly correlated with the level of whey protein denaturation. However, the changes in casein micelle size were highly correlated with the levels of denatured whey proteins that were associated with the casein micelles. The rate of association of the denatured whey proteins with the casein micelles was considerably slower than the rate of denaturation of the whey proteins. Removal of the whey proteins from the skim milk resulted in only small changes in casein micelle size during heating. Re-addition of beta-lactoglobulin to the whey-protein-depleted milk caused the casein micelle size to increase markedly on heat treatment. The changes in casein micelle size induced by the heat treatment of skim milk may be a consequence of the whey proteins associating with the casein micelles. However, these associated whey proteins would need to occlude a large amount of serum to account for the particle size changes. Separate experiments showed that the viscosity changes of heated milk and the estimated volume fraction changes were consistent with the particle size changes observed. Further studies are needed to determine whether the changes in size are due to the specific association of whey proteins with the micelles or whether a low level of aggregation of the casein micelles accompanies this association behaviour. Preliminary studies indicated lower levels of denatured whey proteins associated with the casein micelles and smaller changes in casein micelle size occurred as the pH of the milk was increased from pH 6.5 to pH 6.7.

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    • "Consequently, in the case of light backscatter response, we see a significant difference in intensity at milk pHs of 6.3 and 7.1 with increasing heat treatment temperature (Fig. 4) and a significant positive temperature correlation with light backscatter (r > 0.85, P < 0.05; Table 3). At pH 6.7, however, there are no observable trends or correlations, as it has been observed that only slight micellar association was observed at pH 6.7 (Anema & Li, 2003a). On the other hand, and as expected, with respect to changes in particle size we see a significant difference and a positive correlation with temperature in pH 6.3 milk, only (Figs. 3 and 5). "
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    ABSTRACT: Reconstituted low-heat skim milk with pH adjusted to 6.3, 6.7, and 7.1 was heated at 80 and 90 °C for 10 min to evaluate the relationship between the attachment of denatured whey proteins to the surface of the casein micelle and the intensity of optical light backscatter response. Both optical light backscatter intensity and casein particle size showed a significant negative correlation with pH and positive correlation with heat treatment temperature. When samples were analysed independently by respective pH, there was a significant correlation of both light backscatter and particle size with temperature for samples at a pH of 6.3, and between light backscatter and temperature at pH 7.1. These results show the potential for the use of optical light backscatter techniques as a measurement of changes in casein micelle particle size induced by heat treatment.
    International Dairy Journal 02/2015; 48. DOI:10.1016/j.idairyj.2015.01.017 · 2.30 Impact Factor
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    • "Within the pH range 6.35 and 7.1, it has been reported that proportion of soluble and micelle-bound complexes increase and decrease, respectively, as the pH of heating increases (Anema, 2007, 2008; Anema & Li, 2003b; Donato & Dalgleish, 2006; Vasbinder & de Kruif, 2003). Furthermore, various studies reported that the size of soluble and micelle-bound complexes decreased with increasing pH from 6.3 to 7.3 (Anema & Li, 2003a; del Angel & Dalgleish, 2006; Donato & Dalgleish, 2006; Guyomarc'h, Violleau, Surel, & Famelart, 2010; Renan et al., 2006; Vasbinder & de Kruif, 2003), their structure varied from globular to elongated (Donato & Guyomarc&apos;h, 2009) and the portion of k-CN and other caseins in soluble complexes increased as the pH of heat treatment increased (Donato & Dalgleish, 2006). "
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    ABSTRACT: Skim caprine and bovine milk, adjusted to pH 6.5–7.1 were heated at 90 °C for 10 min. The distribution of caseins, α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) between micellar and serum phases of both types of milk were determined. Depending on milk pH, the involvement of κ-casein (κ-CN) ranged from ∼8 to 52% and from ∼65 to 70% of total κ-CN in bovine and caprine milk, respectively. αS2-Casein and β-casein were only a part of micelle-bound complexes at all pH values in caprine milk. Denatured bovine β-LG and α-LA were involved in both soluble and micelle-bound heat-induced protein complexes. Conversely, denatured caprine β-LG was mainly associated with casein micelles (98–86% at pH 6.5–7.1) and was found in soluble complexes at higher pH (6–12% at pH 6.9–7.1). All denatured caprine α-LA was micelle-bound at all pH values. This knowledge could be very useful for understanding, controlling and modification of technological–functional properties of caprine milk.
    International Dairy Journal 11/2014; 39(1):178–183. DOI:10.1016/j.idairyj.2014.06.006 · 2.30 Impact Factor
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    • "e . , self - aggregation and / or aggrega tion with caseins during heat - treatment prior to spray drying ( Anema & Li , 2003 ) . PH protein ingredients contained more hydro lysed material ( approximately 32% of the material which passed through the size - exclusion column was lower than 10 kDa ) . "
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    ABSTRACT: A whey protein ingredient, in which β-lactoglobulin was selectivity hydrolysed, was evaluated during manufacturing of infant formulae. Three model infant milk formula (IMF) powders were produced containing: non-hydrolysed (NH) proteins (60:40; whey proteins:caseins); partially hydrolysed (PH) caseins and whey proteins; and selectively hydrolysed (SH) whey proteins. After homogenisation, particle size (D[4,3]) of the SH formulae was similar (P > 0.05) to NH formulae and was significantly (P < 0.05) smaller than PH formulae. Prior to spray drying (∼55% w/w), the viscosity of SH formulae (14.8 ± 0.3 mPa s) was significantly lower (P < 0.05) than that of the NH (48.6 ± 0.8 mPa s) or PH formulae (27.6 ± 1.5 mPa s). Surface free fat, wettability and glass transition temperature of powders were not significantly (P > 0.05) different. IMF manufactured with SH ingredients have applications in high dry matter processes with potential for reduced energy costs in spray drying.
    International Dairy Journal 08/2014; 40. DOI:10.1016/j.idairyj.2014.08.012 · 2.30 Impact Factor
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