Effect of pH on the Thermal Denaturation of Whey Proteins in Milk

Abstract

The effect of pH on thermal denaturation of four main whey protein fractions in skim milk was examined by gel permeation FPLC. On heating skim milk at 80 degrees C for 0.5-20.0 min over the pH range 5.2-8.8, the extent of denaturation, based on loss of solubility at pH 4.6, increased with heating time and was usually in the order immunoglobulins > serum albumin/lactoferrin > beta-lactoglobulin > alpha-lactalbumin. Rates of denaturation of the immunoglobulins and the serum albumin/lactoferrin fraction were highest at the lower end of this pH range, whereas those of beta-lactoglobulin and alpha-lactalbumin increased over most of the pH range. The effects of pH, addition of Ca, and reduction of disulfide bonds on the rates of the unfolding and aggregation stages of denaturation are discussed.

The Effect of Molecular Chaperone, Alpha-Crystallin, on the Heat-Induced Aggregation of Beta-lactoglobulin

“…The effect of pH on the aggregation of betalactoglobulin: It has been reported previously that increasing pH increases the rate of aggregation and precipitation of heated beta-lactoglobulin [9,23] . Accordingly, the effect of pH on the rate of aggregation and precipitation of beta-lactoglobulin was studied by heating the sample at 70°C and at different pH values between 6.5 and 8.0.…”

“…Mainly heatinduced aggregation of beta-lactoglobulin occurs through the formation of a dimer-monomer transition state of the protein. This transition state is characterized by a decrease in charge on the histidine residues of beta-lactoglobulin and an increased number of free thiol groups which in turn increases intermolecular thiol/disulfide linkage [23] .…”

Insulinotropic properties of whey protein hydrolysates and impact of peptide fractionation on insulinotropic response

“…This may be linked to differences in the extent of denaturation 261 of the substrates leading to different susceptibility to enzymatic hydrolysis. The percentage denaturation 262 of the proteins in the starting substrates (WP1 and WP2) was quantified by determining their solubility 263 at pH 4.6 using RP-UPLC (Law & Leaver, 2000). The percentage denaturation for β-lactoglobulin was 264 higher in WP2 (22.0 ± 1.0 % (w/w)) compared to WP1 (11.4 ± 1.1 % (w/w)) whereas denaturation of α-265 lactalbumin was similar in both substrates (9.9 ± 1.3 and 8.0 ± 0.7 % (w/w) for WP1 and WP2, respec-266 tively).…”

Role of Whey Protein-Casein Complexes on Yoghurt Texture

“…In skim milk, it has been reported that the denaturation rate of all whey proteins varied throughout the pH range of 6 to 9 (Law and Leaver, 2000). A report by Hoffmann and van Mill (1997) mentioned that the size of the aggregation of -lactoglobulin during heating throughout pH 6 -8, smaller aggregates occurred at pH 8 whereas higher molecular weight aggregates were build up at pH below 7.…”

“…The effect of pH on the formation of whey proteincasein complexes and on their localization either in colloidal or serum phase was studied by several authors (Law and leaver, 2000;Anema and Li, 2003;. Milk heated at pH below 6.6, all denatured whey proteins associated to the surface of the casein micelles whereas milk heated at pH higher than 6.6, few amount of denatured whey proteins associated to the surface of the casein micelles and most of the -casein is dissociated from casein to form whey protein/ -casein complexes in serum phase (Anema and Li, 2003;.…”