A. Negiz et al., MODELING, MONITORING AND CONTROL STRATEGIES FOR HIGH-TEMPERATURE SHORT-TIME PASTEURIZATION SYSTEMS - 2 - LETHALITY-BASED CONTROL, Food control, 9(1), 1998, pp. 17-28
A lethality-based control system was designed to provide accurate cont
rol of a high temperature shout time (HTST) pasteurizer and to process
milk products with a lethality equivalent of 161 degrees F (71.67 deg
rees C) or above for 15 s. This control system provides significant fl
exibility in operating the process and optimizing functional propertie
s of the food components. Multivariable control of an HTST pasteurizer
is implemented by using product total lethality to determine the cont
roller set-points. The equation that relates the temperature and flow
rate combinations to the product total lethality, 161 degrees F (71.67
degrees C), 15 s, was modified to permit overprocessing levels specif
ied by plant personnel. By using this equation and the set-point value
selected for the other variable, set-point values for the temperature
or the flow rate controller were computed. The flow and temperature c
ontrollers are integrated into a real-time monitoring and control syst
em. The monitoring and control system includes the multivariable contr
oller, the lethality rate calculation module, statistical monitoring o
f the total lethality, product flow rate, hot wafer outlet temperature
, and holding tube exit temperature measurements, and the display scre
ens for visual inspection of the monitoring tools. This study attempte
d to achieve compliance of the HTST process operation with the recomme
nded Pasteurized Milk Ordinance by providing a margin between the alar
m limits of the monitoring chart and the safety limits. (C) 1998 Elsev
ier Science Ltd. All rights reserved.