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Abstract
Effect of the high pressure throttling (HPT) process on the shelf life of soymilk and determination of injured microorganisms was investigated. Soymilk was pressurized at 207, and 276 MPa at four different exit temperatures (85, 121, 133 and 145C) and (102, 121, 133, 145C) respectively at three different flow rates (0.75, 1.0, and 1.5 L/min). Inactivation of C. sporogenes in soymilk was higher at 276 MPa as compared to that at 207 MPa when the exit temperature was 121C and hold time was 20.8 s. However, when temperature was increased to 145C more than a 5 log reduction occurred at both pressures and all the three hold times (20.8, 15.6, and 10.4 s). Pressure, time, and temperature were found to be significantly different in the inactivation of C. sporogenes in soymilk. There were more injured cells (0.5 log) at 207 MPa than at 276 MPa. When the temperature and time was increased there were fewer injured cells implicating that spores were completely inactivated rather than injured. The D121 value of C. sporogenes by heat alone was 3 folds more in soymilk than in 0.1% peptone water.