Critical phosphate salt concentrations leading to altered micellar casein structures and functional intermediates

Abstract

We investigated the effect of different phosphate salts on the structural integrity of micellar casein (MC) at pH 7.0. With the increase of salt concentration, a reduction in turbidity was observed for the MC solutions, and it was modeled using an exponential decay function. The inflection point of the model was defined as the first critical salt concentration (C*), and it is suggested that the salt concentration initiates the disintegration of MC. For linear polyphosphates, C* decreased with the number of phosphate groups. Apparent viscosity (η app ) of MC solutions increased with the increase of salt concentration, and they recorded a peak while the turbidity decreased to a minimum. The salt concentration that resulted in the highest η app was identified as the second critical salt concentration (C**). It is hypothesized that the interactions among protein species present in the mixtures are at an optimum state at C**. Both C* and C** were found to be dependent on the MC concentration. The work presented herein supports an understanding of the concentration effect of phosphate salts on MC for structuring dairy products.

Prevention of low-temperature gelation in milk protein concentrates by calcium-binding salts

“…The UF was conducted on 11.34 L of milk concentrated to 3.78 L (permeate was used to determine final volume; 7.56 L). The DF was performed by adding back 7.56 L of distilled water containing 5% of the protein-free permeate generated in the UF step to maintain a minimum ionic environment to prevent micellar dissociation (Culler et al, 2017;Saricay et al, 2019). The DF was performed 4 times with each step removing 7.56 L. The last DF step removed an additional 1.89 L of permeate to create 6-fold concentrated solution in a 1.89-L final volume.…”

“…Calcium-binding salts are known to affect the rheological properties of concentrated milk systems. Calcium-binding salts added above a critical concentration dissociate casein micelles (de Kort et al, 2011;Culler et al, 2017;McCarthy et al, 2017;Saricay et al, 2019) and promote gel formation in milk systems Lucey 2005, 2007; Kaliappan and Lucey, 2011). Mizuno and Lucey (2005) found that tetrasodium pyrophosphate (0.1-2%) promoted gel formation in MPC adjusted to ~3% (wt/wt) protein content, pH 5.8 (com-mon processed cheese pH), and stored overnight.…”

“…This would result in altering the amount of native casein micelles. This hypothesis was based on the observations of Culler et al (2017) and Saricay et al (2019), who found that a specific concentration of calcium-binding salt (dependent on type) resulted in full micellar dissociation. This intermediate concentration would contain a proportion of altered or disassociated casein micelles preventing LT-gelation but retaining other functional properties.…”

“…To test this hypothesis, we first determined the minimum protein content in liquid MPC where LT-gelation occurred, then tested 5 different salts for their ability to prevent LT-gelation. The calcium-binding salts used in this experiment were chosen as previous studies showed critical concentrations where full micellar dissociation was reported (Culler et al, 2017;Saricay et al, 2019). The objective of these experiments was to advance processing interventions that would increase the protein content of liquid MPC at an 80:20 casein: whey protein ratio, for cost effective applications in the food industry.…”

Physicochemical properties of skim milk powder dispersions prepared with calcium-chelating sodium tripolyphosphate, trisodium citrate, and sodium hexametaphosphate

“…The turbidity of a dispersion is a function of particle dimension as well as concentration and compactness (i.e., the ability to reflect light) of particles (Jonassen et al, 2012). At an increased ionic strength, the electrostatic repulsion is weakened due to charge screening effect (Saricay et al, 2019) to cause aggregation of dissociated caseins and therefore the increased D h (Figure 3), whereas casein aggregation lowers particle concentration to cause a continued decrease in turbidity (Figure 2).…”