MODELING, MONITORING AND CONTROL STRATEGIES FOR HIGH-TEMPERATURE SHORT-TIME PASTEURIZATION SYSTEMS - 3 - STATISTICAL MONITORING OF PRODUCT LETHALITY AND PROCESS SENSOR RELIABILITY

Statistical process monitoring (SPM) is used in food processing indust ries to improve productivity and product quality. SPM can also provide information to operators on how close a process is to non-compliance to product safety limits, and carry out periodic checks of sensor accu racy at high frequency. Traditional SPM tools such as Shewhart charts are not appropriate for continuous food processes because of autocorre lation in data. Four alternative SPM techniques are presented and appl ied to high temperature short time (HTST) dairy pasteurization. The st udy attempted to achieve compliance of the HTST process operation with the recommended Pasteurized Milk Ordinance by providing a margin betw een the alarm limits of the monitoring chart and the safety limits. Mo nitoring of residuals and parameter change detection techniques ave us ed for monitoring processes with autocorrelated variables. Hotelling's T-2 and residuals of canonical variates techniques are used for monit oring multivariable processes. (C) 1998 Elsevier Science Ltd. All righ ts reserved.