The Coagulation of Differently Sized Casein Micelles by Rennet

Abstract

Fractions of bovine casein micelles of different sizes were prepared by sucessive centrifugation steps, and dilute suspensions of the different fraction were reacted with rennet. The molecular weight increas with time after addition of rennet was measured by light scattering. After an initial lag stage, where the increase was zero, and a short intermediate stage, the molecular weight became linearly proportional to time, indicating complete conversion of the ϰ‐casein substrate by the enzyme. The slope of the final portion of the growth profile can be used to define values of the Smoluchowski rate constant governing the aggregation. No significant differences in this constant were found with mielles of different sizes, and the value of the rate constant suggested that the aggregation reaction of completely renneted micelles is only moderately retarded relative to the diffusion controlled process, even at room temperature.

Factors affecting the clotting properties of sheep milk

“…This follows a Smoluchowskian process of aggregation in which the speed of curd formation depends on the molar concentration of the casein micelles, which in turn increases the probability of any two micelles coming into contact and becoming aggregated. 32,39 The higher concentration of casein micelles present in sheep milk explains why the rate of ®rming was faster and less affected by pH in sheep milk than in cows' milk.…”

Influence de trois haplotypes des caséines αsl, β et Κ fréquents en race bovine Normande sur la composition du lait et l'aptitude à la fabrication fromagère

“…Les laits BBB, un peu moins riches en teneur en caséine K que les laits CA2B possèdent des micelles de taille intermédiaire. Ces résultats sont en parfait accord avec l'ensemble des publications sur la relation entre la caséine K et ses principaux variants génétiques (variants A et B) et la dimension moyenne des micelles de caséines (Rose et Colvin, 1966;Morini et al, 1975;Mc Gann et al, 1980 ;Dalgleish et al, 1981 ;Davies et Law, 1983;Mc Lean et al, 1984;Grandison et al, 1985 ;Ford et Grandison, 1986). Les laits des différents haplotypes se différen-cient aussi par leur aptitude à la coagulation par la présure et les résultats obtenus confirment pour les haplotypes les travaux sur les variants des caséines K et p. Ainsi, il apparaît clairement que l'effet favorable associé au variant B de la caséine K sur le temps de coagulation et le raffermissement du gel est renforcé par celui de la caséine p (Mariani et Leoni, 1985 ;Pagnacco et Caroli, 1987).…”

Characterisation of whey drainage kinetics during soft cheese manufacture in relation with the physicochemical and technological factors, pH at renneting, casein concentration and ionic strength of milk

“…The caseinomacropeptide (CMP) part of κ casein and also the mineral equilibria between casein micelles and the diffusible phase play a prominent part in micelle stability [8,12,13]. The release of CMP from κ casein by rennet, and the solubilisation of the colloidal calcium phosphate by starter acidification of milk [5,6,15,18] allow a decrease of the stabilizing energetic barrier between casein micelles [21], allowing thereby a closer contact between micelles leading to the formation of a solid network entrapping the aqueous phase.…”