EVALUATION OF METHODS TO MEASURE COAGULATION TIME OF ULTRAFILTERED MILK

The coagulation time (CT) of ultrafiltered (UF) milk is difficult to measure conventionally by visualizing a fracture of film in a rotating tube/bottle. This paper evaluates the suitability ot several instrumental methods to measure CT. The CT of pasteurized skim milk samples (62-degrees-C for 30 min) concentrated by ultrafiltration from 1 X to 4X pH 7.0 (unadjusted) were measured in triplicate by using Nametre viscometer, hot wired method, rigidity modulus monitor and Formagraph. The average CT measured by four methods decreased form 55 to 20 min (P < 0.05) with an increase in milk concentration (1X to 4X). The 1X-UF milk had higher CT (55 min) compared to control (non UF) milk (48.5) inspite of similar composition (P < 0.05). Formagraph provided higher CT at all levels of concentration compared to other methods except tor the control and 1X-UF milk where the rigidity modulus monitor failed to measure CT The CT values were not significantly different between Nametre viscometer and hot wire method. However, Nametre viscometer was considered a better instrument because of its better precision.