Does ultrafiltration have a lasting effect on the physico-chemical properties of the casein micelles?

Abstract

The objective of this work was to determine if concentration of milk using ultrafiltration (in the absence of diafiltration) affects the physico-chemical properties of the casein micelles. The milk, once concentrated, was brought back to its original concentration and the physico-chemical properties as well as its susceptibility to rennet induced gelation were assessed. Although much is understood on the renneting behavior of concentrated milk, no information is available on how (or if) ultrafiltration per se modifies the properties of the micelles. Two times (2×) or five times (5×) concentrated milk (based on volume reduction) was prepared by ultrafiltration. Casein micelles were redispersed in their corresponding permeates and dialyzed against untreated skim milk. The stability of the casein micelles, their scattering properties, and the renneting properties were observed under the same volume fraction and ionic conditions of the skim milk control. There was a higher susceptibility to aggregation and a lower gel stiffness for the reconstituted micelles from the 5× milk compared to the 2× milk. 5× Ultrafiltration induced losses of calcium from the micelle, while 2× milk showed similar value as the control. The results suggest that the process of ultrafiltration affected the internal structure of the

Effect of concentration, homogenization and stabilizing salts on heat stability and rheological properties of cow skim milk ultrafiltered retentate

“…In UF process, highly significant (P \ 0.01) reduction in the pH of retentates was observed from 19 (pH 6.60) to 59 (pH 6.41) concentration (Table 1). The observed decrease in pH was in good agreement with the previously reported results (Huppertz et al 2004;Karlsson et al 2005;Ferrer et al 2011). The concentration of milk salts (Ca 2?…”

“…increases during UF process which changes the cationic profile of milk based on their association with proteins, but total calcium to protein ratio decreases with increase in CF due to passage of soluble calcium in permeate (Ferrer et al 2011;Sikand et al 2013). Moreover, marked decreased (P \ 0.01) in the pH of 59 Na-K was also observed which was attributed to the DF of 59 UFR sample with NaCl-KCl added RO water (Table 1).…”

“…Caseins are present as micelles with an average diameter of about 200 nm in colloidal suspension in milk. Casein micelles are spherical in shape, fully covered by hairy layer of j-casein (Ferrer et al 2011) that delivers steric and charge stabilization as well as zeta (f) potential of -20 mV to it (De Kruif and Holt 2003). Slight change in salt equilibrium of milk, induces significant change in structure and functional properties of casein micelles.…”

Changes in particle size, calcium and phosphate solubilization, and microstructure of rehydrated milk protein concentrates, prepared from partially acidified milk

“…A higher concentration of soluble caseins was present in the supernatant of reconstituted MPC samples (lanes 2 to 9) compared to skim milk (lane 1) despite the equal initial protein content 3.2% (w/ w). It has been previously demonstrated that after membrane concentration, there is an increase in soluble caseins in both fresh or reconstituted retentates (Ferrer et al 2011;Sandra and Corredig 2013). The soluble fraction varies depending on the concentration and the presence of DF (Li et al 2015).…”

“…Mineral equilibrium also is of importance in determining the rehydration and functional properties of MPC, such as renneting and emulsifying properties (Ferrer et al 2011;Ye 2011;Sandra and Corredig 2013). Imaging techniques such as scanning electron microscopy (SEM) and transmission electron microcopy (TEM) have been employed to study the microstructure of dairy powders in the dry state (Gaiani et al 2007;Tamime et al 2007) or after rehydration (Havea 2006;Mimouni et al 2010b).…”