Influence of Urea on Viscoelastic Properties and Microstructure of Acid-induced Milk Gel

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

“…Heat treatment performed by the authors (80 °C/30 min) may have led to a smaller extent of aggregation of the whey proteins, yielding less dramatic heatinduced changes in the gelation profile of milk (gelation pH 5.1, final G′ ) 200 Pa) than that applied in this study (90 °C/ 10 min). With a possibly lower effect of heat treatment, that of prerenneting could then be seen, in agreement with Niki et al (50), who used medium-heat skim milk powder and also observed rennet-induced changes in the gelation profile of acid gels. In extensively heated milk, it seems that increased G′ values may rather be obtained when acid gels are made using simultaneous renneting and acidification, providing that the rate of κ-casein hydrolysis is finely tuned throughout acidification for a synergy to occur (51)(52)(53)56).…”

“…Increasing the rate of conversion of κ-casein into para-κ-casein from 0 to ∼65% caused the gelation pH to shift from 4.9 to 5.5 in unheated milk and from 5.4 to 5.6 when heat treatment and renneting were combined (Table ). This effect was also reported when unheated – or heated skim milk had been renneted to similar extents prior to acidification. In these studies, it is proposed that prerenneting of the casein micelles allowed hydrophobic attraction to overcome electrostatic repulsion at higher pH values than in untreated milk.…”

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

“…The renneting creates hydrophobic sites on the surface of the casein micelles, as the binding of the modified heat-induced complexes on the micelles is supposed to do. In agreement with our findings, pre-renneting milk induced a significant increase in gelation pH, final gel strength and pore size in the resulting acid gels (Gastaldi et al, 2003;Li & Dalgleish, 2006;Lucey, Tamehana, Singh, & Munro, 2000Niki, Ito, Motoshima, Watanabe, & Tsukasaki, 2003). However, the hypothesis that the soluble complexes interact with the casein micelles prior to gelation only stands so far for un-modified heated skim milk (Alexander & Dalgleish, 2005;Donato, Alexander, & Dalgleish, 2007;Guyomarc'h, Jemin, Le Tilly, Madec, & Famelart, 2009).…”

How to tailor heat-induced whey protein/κ-casein complexes as a means to investigate the acid gelation of milk—a review

“…The method has been shown to increase the pH of acid gelation of the casein micelles in milk (Cases et al 2003;Gastaldi et al 1996;Li and Dalgleish 2006;Niki et al 2003). Renan et al (2007), Anema et al (2007) and Mollé et al (2006) showed that κ-casein as involved in the heat-induced whey protein/κ-casein complexes of milk could also be cleaved by chymosin.…”

“…Deglycosylation (Cases et al 2003) or renneting (Gastaldi et al 1996;Li and Dalgleish 2006;Niki et al 2003) has already been performed on the κ-casein in casein micelles or whey protein/κ-casein complexes. The processes are likely to readily expose hydrophobic regions of the κ-casein as they cleave hydrophilic moieties of the protein.…”