Control of Heat-Induced Aggregation of Whey Proteins Using Casein

Abstract

The ability of alphas1/beta-casein and micellar casein to protect whey proteins from heat-induced aggregation/precipitation reactions and therefore control their functional behavior was examined. Complete suppression (>99%) of heat-induced aggregation of 0.5% (w/w) whey protein isolate (pH 6.0, 85 degrees C, 10 min) was achieved at a ratio of 1:0.1 (w/w) of whey protein isolate (WPI) to alphas1/beta-casein, giving an effective molar ratio of 1:0.15, at 50% whey protein denaturation. However, in the presence of 100 mM NaCl, heating of the WPI/alphas1/beta-casein dispersions to 85 degrees C for 10 min resulted in precipitation between pH 6 and 5.35. WPI heated with micellar casein in simulated milk ultrafiltrate was stable to precipitation at pH>5.4. Protein particle size and turbidity significantly (P<or=0.05) increased from an initial diameter of 165.5 nm in the unheated mixture to 272 nm following heating at 85 degrees C for 10 min at pH 6. Whey protein denaturation was significantly (P<or=0.05) promoted when heated in the presence of micellar casein, but whey protein aggregation was controlled down to pH 5.4. The protective behavior of alphas1/beta-casein and micellar casein differed in that the former inhibited denatured whey protein aggregation, whereas the latter system promoted denaturation but controlled aggregation.

Controlling heat induced aggregation of whey proteins by casein inclusion in concentrated protein dispersions

“…As expected, all main factors substantially affected aggregation of WPs, which was in line with previous observations related to the effect of pH (Dissanayake et al, 2012), temperature (Singh & Havea, 2003) and inclusion of caseins (O'Kennedy & Mounsey, 2006). Increasing concentration of casein in the mixtures significantly (P < 0.05) reduced the average particle size of WP aggregates upon heating at pH further away from the isoelectric point of these proteins (6.7 and 7.5).…”

“…3) also suggested that part of the casein micelles may not have directly incorporated into aggregates formed with WPs at pH 7.5 when high casein content (casein:WP 30:70) was present. Some previous studies have reported an involvement of casein micelles via aggregate formation with WPs, but under different experimental conditions (Beaulieu, Pouliot, & Pouliot, 1999;O'Kennedy & Mounsey, 2006). In contrast, the dispersion with low casein content (casein:WP 5:95) at the same pH displayed a single broad peak at~40 nm with a wide distribution (~20e550 nm) indicating a higher level of WP aggregation.…”

The dominating effect of ionic strength on the heat-induced denaturation and aggregation of β-lactoglobulin in simulated milk ultrafiltrate

“…It should also be noted these samples contain 0.018% a-lactalbumin as a contaminant which may have some effect during heating. A significant increase in turbidity was not observed when b-lg was heated in the pH range Mounsey, 2006). This pH-dependant aggregation behaviour is typical for b-lg heated under low ionic strength conditions where the denaturation rate is limited by its ability to aggregate (Verheul et al, 1998).…”

Acidic residue modifications restore chaperone activity of β-casein interacting with lysozyme

“…␤-casein and ␣ s -casein have molecular chaperone-like properties [7,8]. Caseins are also shown to decrease turbidity of whey proteins under stress conditions [9]. ␣ s -casein exhibits a considerable anti-aggregation activity [4,7,8].…”