Comparison of total milk-clotting activity measurement precision using the Berridge clotting time method and a proposed optical method

摘要

An objective measurement technique is needed to simplify the determination of total milk-clotting activity (a_t) 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 milk flocculation. An optical method based on changes in infrared light back-scatter at 880 nm during milk coagulation is proposed as an alternative, objective method to Berridge clotting time to eliminate the operator's subjectivity from the IDF Standard 157: 2007. The Berridge clotting time method and a proposed optical method were compared using 29 replications to determine the precision of a_t measurements. The light backscatter profiles collected during the coagulation process were analyzed with five optical time parameters determined for each profile. The a_t, expressed in International Milk-Clotting Units (IMCU mL~(-1)), was calculated using Berridge clotting time and each of the five optical time parameters. The calculated milk-clotting activities were compared statistically to determine differences between measurement methods. No significant differences were found between the a, determined using the Berridge clotting time and the optical time parameters, t_(2min) and t_(2min2).- Preferred optical time parameters t_(max) and t(2min) were recommended. The results show that the proposed optical method based on measurement of changes in infrared light backscatter is a potential objective method for a, measurement.