Thermal inactivation of chymosin during cheese manufacture

Abstract

The aspartic proteinase, chymosin (EC 3.4.23.4) is the principal milk clotting enzyme used in cheese production and is one of the principal proteolytic agents involved in cheese ripening. Varietal differences in chymosin activity, due to factors such as cheese cooking temperature, fundamentally influence cheese characteristics. Furthermore, much chymosin is lost in whey, and further processing of this by-product may require efficient inactivation of this enzyme, with minimal effects on whey proteins. In the first part of this study, the thermal inactivation kinetics of Maxiren 15 (a recombinant chymosin preparation) were studied in skim milk ultrafiltration permeate, whole milk whey and skim milk whey. Inactivation of chymosin in these systems (at pH 6.64) followed first order kinetics with a D45.5 value of 100±21 min and a z-value of 5.9±0.3 °C. D-Values increased linearly with decreasing pH from 6.64 to 6.2, while z-values decreased as pH decreased from 6.64 to 6.4, but were similar at pH 6.4 and 6.2. Subsequent determination of chymosin activity during manufacture of Cheddar and Swiss-type cheese showed good correlations between predicted and experimental values for thermal inactivation of chymosin in whey. However, both types of cheese curd exhibited relatively constant residual chymosin activity throughout manufacture, despite the higher cooking temperature applied in the manufacture of Swiss cheese. Electrophoretic analysis of slurries made from Cheddar and Swiss cheese indicated decreased proteolysis due to chymosin activity during storage of the Swiss cheese slurry, but hydrolysis of sodium caseinate by coagulant extracted from both cheese types indicated similar levels of residual chymosin activity. This may suggest that some form of conformational change other than irreversible thermal denaturation of chymisin takes place in cheese curd during cooking, or that some other physico-chemical difference between Swiss and Cheddar cheese controls the activity of chymosin during ripening.

Proteolysis and related enzymatic activities in ten Greek cheese varieties

“…Rather higher levels of residual chymosin have been found in the hard type cheeses, in which the cooking conditions are in general milder and the salt content higher than that in Gruyere type cheeses (Table 1). Hayes et al (2002) have found that in both Cheddar and Emmental curd pieces and 1-day-old cheeses, the residual chymosin activity was similar, contrast to the decreased chymosin-induced proteolysis observed during storage of Swiss cheese slurry. It has been reported that during cooking at temperatures up to 55°C, the enzyme is partially and reversibly denatured and can be partially reactivated during ripening (Hayes et al 2002(Hayes et al , 2004.…”

“…Hayes et al (2002) have found that in both Cheddar and Emmental curd pieces and 1-day-old cheeses, the residual chymosin activity was similar, contrast to the decreased chymosin-induced proteolysis observed during storage of Swiss cheese slurry. It has been reported that during cooking at temperatures up to 55°C, the enzyme is partially and reversibly denatured and can be partially reactivated during ripening (Hayes et al 2002(Hayes et al , 2004. Moreover, according to Hayes et al (2001), residual chymosin activity in high-cooked cheeses may be partially attributed to cathepsin D, which is less heat-labile than chymosin and hydrolyses the assay substrate similarly to chymosin under the same conditions.…”

“…According to Garnot and Mollé (1987), an increase of pH in the range from 6.50 to 6.75 at 51°C for 30 min results in a reduction of residual chymosin activity by about 60%. Also, Hayes et al (2002) report that there is a 17-fold linear increase in D values of chymosin at 56.5°C as pH of the skim milk decreases from 6.64 to 6.20. Moreover, the "survival" of chymosin after pasta filata processing may be related to the findings of Bansal et al (Bansal et al 2007), who report that pH reduction to <5.6 increases the interaction of coagulant with casein micelles.…”

Effect of Post Manufacture Thermal Dip Treatment on Proteolysis of Commercial String Cheese During Storage

“…Chymosin is the principle enzyme responsible for milk coagulation (Hayes et al, 2002) and is essential for cheese ripening (Fox and Law, 1991). Rennet cleaves κ-CN at the Phe 105 -Met 106 bond, resulting in a para-κ-CN and a hydrophilic glycomacropeptide (Visser, 1993;Hayes et al, 2002) as shown in Figure 5.…”

“…Rennet cleaves κ-CN at the Phe 105 -Met 106 bond, resulting in a para-κ-CN and a hydrophilic glycomacropeptide (Visser, 1993;Hayes et al, 2002) as shown in Figure 5. As mentioned earlier, chymosin causes the initial softening of cheese where the breakdown of α s1 -CN to α s1 -I-CN takes place (Creamer and Olson, 1982;Sheehan et al, 2007;Feeney et al, 2002).…”