In situ electrical conductivity measurement of select liquid foods under hydrostatic pressure to 800 MPa

Electrical conductivity of select liquid foods and salt solutions was measured in situ during high pressure processing using a specially designed parallel electrode conductivity cell. Cell constants at atmospheric pressure were determined with KCl standards and calculated against standard data, while cell constants under pressure were estimated assuming isotropic compression. Measured conductivities of NaCl solutions under pressure were within 5.7% of previously reported data at pressures up to 800 MPa and temperatures to 61 °C. Electrical conductivity of NaCl and KCl solutions, orange juice, apple juice, tomato juice, and soybean oil were measured in triplicate in 100 MPa increments from 0.1 to 800 MPa. 0.01 m salt solutions were measured at 25 and 50 °C; 0.1 m salt solutions, juice and oil samples were measured at 25 °C. Results show conductivity of salt solutions and juice samples increased as a function of pressure, peaking between 200 and 500 MPa and decreasing above 500 MPa. Except for soybean oil, pressure had a significant effect (p < 0.01) on electrical conductivity for all samples. Temperature had a significant effect (p < 0.01) on electrical conductivity of 0.01 m salt solutions at all pressures. Conductivity of soybean oil was too low to be measured at atmospheric and pressurized conditions.