Acid Gelation Properties of Heated Skim Milk as a Result of Enzymatically Induced Changes in the Micelle/Serum Distribution of the Whey Protein/κ-Casein Aggregates

Abstract

Changes in the acid gelation properties of skim milk as a result of variations in the micelle/serum distribution of the heat-induced whey protein/kappa-casein aggregates, induced by the combination of heat treatment and limited renneting, were investigated. No dramatic change in the zeta potential or the isoelectric point of the casein micelles was suggested, whether the aggregates were all attached to the casein micelle or not. Fluorescence intensity measurement using 8-anilino-1-naphthalenesulfonic acid (ANS) showed that the heat-induced aggregates were highly hydrophobic. Dynamic oscillation viscosimetry showed that acid gelation using glucono-delta-lactone (GDL) started at a higher pH value in prerenneted milk. However, no change in the gelation profile of skim milk could be related to the proportion of aggregates bound to the surface of the casein micelles. The results support the idea of an early interaction between the serum aggregates and the casein micelles on acidification.

Formation and properties of the whey protein/κ-casein complexes in heated skim milk – A review

“…In agreement with previous studies on heated solutions of β-lactoglobulin [160] or on ultracentrifugal fractions of heated milk [24,91], serum heat-induced complexes bear a significantly higher surface hydrophobicity than unheated casein micelles [96]. Other results strongly suggest that the micelle-bound complexes also increase surface hydrophobicity of the heated casein micelle [74]. Anema et al [8] and Mollé et al [131] have evidenced that κ-casein involved in the heat-induced whey protein/κ-casein complexes was cleaved by chymosin, which accounts for the little or no difference in the final amounts of caseinomacropeptide (CMP) released in heated and unheated skim milk on renneting [8,188].…”

“…These values compared with those of the casein micelles. The complexes precipitated in the pH range 3.5-5.5 in the same medium and temperature [74,96]. Their apparent isoelectric pH value, or pI, was found to be 4.4-4.5 and was only slightly lower than that of the casein micelles (∼ pH 4.7).…”

Increasing the hydrophobicity of the heat-induced whey protein complexes improves the acid gelation of skim milk

“…The corresponding confocal images showed thick, particulate gels, which is consistent with the rather low G 0 values (not shown). To the authors' knowledge, no report can be found in the literature of the rheological behaviour of 50 g kg À1 heated skim milk at 25 C, but values somewhat higher than 200 Pa could have been expected (Guyomarc'h, Renan, Chatriot, Gamerre, & Famelart, 2007;Lucey, Tamehana, Singh, & Munro, 1998a, 1998bLucey, Teo, Munro, & Singh, 1997;Van Marle & Zoon, 1995). This may be the result of the recombination procedure.…”

Effects of κ-Casein Dissociation from Casein Micelles on Cheese Curd Formation

“…It has been reported that in heated defatted milk, part of κ-CN is dissociated from micelles (Guyomarc'h et al, 2003;Guyomarc'h et al, 2007;Vasbinder et al, 2003). In the present work, the state of the not involved in the milk clotting of casein micelles, even when para-κ-CN was formed by the chymosin reaction.…”