Research Accomplishment Reports 2007

Improvements of Thermal and Alternative Processes for Foods

F.A. Payne
Department of Biosystems and Agricultural Engineering

 

Project Description

An objective measurement technique is needed to simplify the determination of total milk-clotting activity of rennets and other milk coagulating enzymes. IDF Standard 157: 2007/ISO 11815 is the current standard method for bovine rennets and measures milk-clotting activity by visually determining the Berridge clotting time (i.e., time of appearance of flocks of renneted standard milk substrate on the wall of a rotating test tube). The IDF Standard 157: 2007 method is somewhat subjective because it depends on an operator’s skill to consistently identify flocculation.

Impact

A coagulation measurement apparatus was designed and developed for measuring infrared light backscatter during milk coagulation. Two vats were designed into the apparatus to make exact and precise comparisons feasible. Each vat was instrumented to measure infrared light backscatter, temperature and pH during coagulation. Precise temperature control was confirmed for the coagulation measurement apparatus.  A computerized data acquisition system was developed and used to collect, store and analyze the data for determination of optical time parameters during milk coagulation.

A test was designed to compare the Berridge clotting time method with the proposed optical method using infrared light backscatter for repeatability of measurement of total milk-clotting activity (IMCU /mL). The Berridge clotting time method and a proposed optical method were compared using 35 replications to determine the repeatability of total milk-clotting activity measurement. The light backscatter profiles collected during the coagulation process were analyzed with five optical time parameters determined for each profile. The total milk-clotting activity, expressed in International Milk Clotting Units per mL of enzyme (IMCU/mL), was calculated using Berridge clotting time and each of the five optical time parameters. The calculated IMCUs were compared statistically to determine differences between measurement methods.

No significant differences were found between the IMCUs determined using the Berridge clotting time and those obtained using any of the five optical time parameters. Preferred optical time parameters were recommended. The results show that the proposed optical method measuring infrared light backscatter is a potential objective method for total milk-clotting activity measurement.

Publications

Tabayehnejad, N., Castillo, M. and Payne, F. A. (2008) Comparison of measurement repeatability of the Berridge clotting time method with an optical method for total milk-clotting activity determination, Int. Dairy J. (submitted)