Effects of Heat Treatment and Post-Treatment Holding Time on Rennet-Clotting Properties of Milk

• Main Author: Ustunol, Zeynep
• Format: Others
• Published: DigitalCommons@USU 1983
• Subjects: Heat Treatment; Holding Time; Milk; Food Science
• Online Access: https://digitalcommons.usu.edu/etd/5290; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=6345&context=etd

Samples of raw whole milk were heated at L5, 50 and 75 C for 0, 30, 60, llU and 240 min. After heat treatment each sample was subdivided and portions held at O C for 0, 30, 60 and 120 min. In a second experiment samples of milk were heated at 25 and 50 C for the same lengths of time as before but this time at 75 C for only 5, 10, 15 and 20 min. A constant holding time of 30 min was used after the heat treatments. Following the various heat treatments pH of each sample was measured and rennet clotting properties of milk at a constant rennet concentration were determined using the Formagraph instrument. The 75 C heat treatment of both experiments was left out from the statistical analysis. Results obtained in the first experiment indicate that cold storage at O C for up to 120 min has no significant effect on pH or on rennet-clotting properties of milk. Milk that was heated at 75 C for 30 min or longer did not coagulate. Results of the second experiment show that increase from 25 C to 50 C and extended heating time both reduce pH and clotting time. However, curd firming rate and cutting time are only affected by the length of time that the milk is heated. When milk is heated at 75 C coagulation time, curd firming rate and cutting time of curd are severely retarded.