46-10 |
|
A. V. ARDISSON, S. S. H. Rizvi, and C. I. Moraru. Institute of Food Science, Cornell University, Stocking Hall, Ithaca, NY 14853 Coagulation time is an essential parameter for quality control, as well as for planning the machinery operations during cheese making. A soft coagulum causes loss of milk solids in whey, while too hard a coagulum results in poor product quality. Precise identification of coagulation time is thus essential for successful cheese making. The objective of this study was to determine the rennet coagulation properties of concentrated cheese milk from microfiltration retentates (CCMR). The dynamic moduli (G', G") and tan d were measured as a function of time and related to k-casein hydrolysis. Pasteurized skim milk was microfiltered to 8 times its original weight at 50 ºC using a 0.1mm microfiltration membrane. The milk was gradually acidified during microfiltration to pH 6.0 using glucono-d-lactone (GDL) (1.6 g/l skim milk). The retentate was standardized with cream and acidified with 1.7% GDL. Rennet was added at a level of 3.92 ml/g casein. The viscoelastic properties during coagulation were determined using mechanical spectroscopy. Time sweeps were performed in the linear viscoelastic region at 36 °C. k-casein hydrolysis was monitored measuring the glycomacropeptide release as soluble nitrogen in 8% TCA. The coagulation was observed to follow a three-stage process. The peak in G' was reached about 10 times faster for CCMR as compared to the control milk, while the time required for 100% k-casein hydrolysis in CCMR was 50 minutes vs. 20 minutes for the control. When the CCMR was diluted with ultrafiltration permeate to 2.6% casein, the rate of k-casein hydrolysis became identical to the control. This indicates a complex influence of the pH and casein concentration of the CCMR, coupled with a slower diffusion rate of rennet in the concentrated system. These results suggest a different rennet coagulation behavior of CCMR as compared to regular cheese milk, which has to be considered during cheese manufacturing.
Session 46, Dairy Foods: General
|