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L. J. YU, Dept. of Bioresource Engineering, McGill Univ., Macdonald Campus, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, QC H9X 3V9, Canada and M. O. Ngadi, Dept. of Agricultural and Biosystems Engineering, McGill Univ., 21111 Lakeshore Rd., Macdonald-Stewart Bldg., Rm. MS1-027, Sainte-Anne-de-Bellevue, QC H9X 3V9, Canada. Raw milk cheese has desired flavor and taste. However, its safety is not guaranteed. The Pulsed Electric Field (PEF) treatment is a promising non-thermal pasteurization method, which may provide safe and fresh-like foods. Previous studies showed the possibility of pasteurizing milk by PEF instead of heat in cheese making. Coagulation is one of the most important steps in cheese production. However, no studies have surveyed effects of PEF treatment on coagulation properties of milk. The objectives of this study were to determine the coagulation properties of PEF treated milk and compare with those of raw milk. PEF treatment was conducted in a continuous chamber by a bipolar square waveform with pulse width of 2 ms. The maximum 20 kV/cm electric field intensity (E), maximum 150 pulses and up to 55o C outlet temperatures were applied. Dynamic rheological test was conducted to analyze coagulation properties because it non-destructively measures the viscoelasticity of the curd during its formation. AR2000 rheometer (TA Instruments, New Castle, DE) with a concentric cylinder geometry was used. Storage modulus G¢ versus time was measured and the maximum G¢ was named as firmness of the curd. The negative slope of the logarithmic function of the difference between G¢ and firmness over time was defined as Coagulation Rate (CR). Results indicated E, temperature, and pulse number significantly (p<0.05) affected coagulation properties. With E and pulse number increasing firmness increased, while CR decreased. However, higher pulse number and E led to adverse effect on these two parameters. With outlet temperature increasing, firmness and CR decreased. Milk treated at 15oC, 10kV/cm, 90 pulses showed highest firmness (149.2 Pa), and raw milk showed highest CR (0.0019). PEF is a potential alternative method for milk pasteurization and cheese production. Coagulation of milk could be useful in predicting quality characteristics of final cheese products.
Session 34, Nonthermal Processing: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |