The Role of β-lactoglobulin in the primary phase of rennin action on heated casein micelles and heated milk

Abstract

SummaryIt has been shown that the inhibition caused by heat treatment, of the primary phase of rennin action on casein micelles, is dependent on the presence of β-lactoglobulin. The degree of inhibition increased with increasing amounts of added β-lactoglobulin for both heated casein micelles and heated skim-milk to a constant value. The results are fully consistent with the hypothesis that the inhibition is caused by complex formation between β-lactoglobulin and κ-casein when milk is heated.

The effect of ultra high-pressure homogenization (UHPH) on rennet coagulation properties of unheated and heated fresh skimmed milk

“…The heated milk also showed a lower level of total k-casein hydrolysis (about 10-15% less) than unheated milk, even though a higher chymosin concentration was used, and the reaction was studied for a longer time. This finding is in agreement with the results of Wheelock andKirk (1974), van Hooydonk et al (1987) and Reddy and Kinsella (1990), and has been attributed to the complex formation between b-lg and k-casein providing electrostatic and steric hindrance between rennet and k-casein. The level of inhibition of CMP release depends on heating time (and probably the method of heating), pH, temperature and b-lg concentration (Reddy & Kinsella, 1990).…”

Effect of pH at heat treatment on the hydrolysis of κ-casein and the gelation of skim milk by chymosin

“…Many studies suggested a delay in the primary phase when milk was heated, and it was thought that the interaction between denatured whey protein and k-casein at the casein micelle surface inhibited access of the chymosin enzyme to the susceptible bond on k-casein (Dalgleish, 1992;Hyslop, 2003;Leaver et al, 1995;Lucey, 1995;Reddy & Kinsella, 1990;Walstra & Jenness, 1984;Wheelock & Kirk, 1974;Wilson & Wheelock, 1972). However, other studies found little or no effect of heating on the primary phase of the renneting reaction (Marshall, 1986;van Hooydonk et al, 1987;Vasbinder et al, 2003).…”

“…However, there are conflicting views on the mechanism for this retardation in coagulation time. Most reports suggest that the interaction of denatured whey proteins with the k-casein inhibits the enzyme action of chymosin on k-casein (Dalgleish, 1992;Hyslop, 2003;Leaver, Law, Horne, & Banks, 1995;Lucey, 1995;Reddy & Kinsella, 1990;Walstra & Jenness, 1984;Wheelock & Kirk, 1974;Wilson & Wheelock, 1972). However, other reports suggest a negligible effect of heating on the primary phase of the chymosin reaction, and it has been suggested that the secondary phase of the coagulation process is inhibited by the presence of denatured whey proteins (Marshall, 1986;van Hooydonk, de Koster, & Boerrigter, 1987;Vasbinder, Rollema, & de Kruif, 2003) or by the reduced calcium ion activity induced by heating (Schreiber, 2001;van Hooydonk, Hagedoorn, & Boerrigter, 1986).…”

Effects of β-lactoglobulin and κ-casein genetic variants and concentrations on syneresis of gels from renneted heated milk

“…This was particularly evident with AMM containing a low /c-casein concentration, and coagulation had not occurred 35 min after rennet addition with both of these samples. The poor coagulation properties of these heated AMM samples containing a high /?-lg concentration was probably due to the complex formed between /?-lg and /c-casein inhibiting hydrolysis of/c-casein by chymosin (Wheelock & Kirk, 1974). A low K-casein concentration has been associated with poor coagulation properties (Okigbo et al 1985) due probably to the larger casein micelles (Ford & Grandison, 1986).…”