David J. Armstrong

Modeling, monitoring and control strategies for high temperature short time pasteurization systems — 3. Statistical monitoring of product lethality and process sensor reliability

Abstract Statistical process monitoring (SPM) is used in food processing industries 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 accuracy at high frequency. Traditional SPM tools such as Shewhart charts are not appropriate for continuous food processes because of autocorrelation in data. Four alternative SPM techniques are presented and applied to high temperature short time (HTST) dairy pasteurization. The study attempted to achieve compliance of the HTST process operation with the recommended Pasteurized Milk Ordinance by providing a margin between the alarm limits of the monitoring chart and the safety limits. Monitoring of residuals and parameter change detection techniques are used for monitoring processes with autocorrelated variables. Hotellings T2 and residuals of canonical variates techniques are used for monitoring multivariable processes.

Automated control of high temperature short time pasteurization

Abstract Cascade and multivariable control of a high temperature short time (HTST) pasteurization system were tested and compared with the performance of singleloop feedback control. Multivariable control was implemented on the basis of computations of product temperatures that yield equivalent lethality at a residence time of 15 s at 161 °F in the holding tube. Both cascade and multivariable controllers reduced product temperature fluctuations and overshoot compared to single-loop feedback control. Multivariable control was based on on-line computation of equivalent total lethality and it permitted operation at variable flow rates or at the most desirable temperatures for product quality and functionality.

Modeling, monitoring and control strategies for high temperature short time pasteurization systems - 2. Lethality-based control

Abstract A lethality-based control system was designed to provide accurate control of a high temperature short time (HTST) pasteurizer and to process milk products with a lethality equivalent of 161 °F (71.67 °C) or above for 15 s. This control system provides significant flexibility in operating the process and optimizing functional properties of the food components. Multivariable control of an HTST pasteurizer is implemented by using product total lethality to determine the controller set-points. The equation that relates the temperature and flow rate combinations to the product total lethality, 161 °F (71.67 °C), 15 s, was modified to permit overprocessing levels specified 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 controllers are integrated into a real-time monitoring and control system. The monitoring and control system includes the multivariable controller, the lethality rate calculation module, statistical monitoring of the total lethality, product flow rate, hot water outlet temperature, and holding tube exit temperature measurements, and the display screens for visual inspection of the monitoring tools. This study attempted to achieve compliance of the HTST process operation with the recommended Pasteurized Milk Ordinance by providing a margin between the alarm limits of the monitoring chart and the safety limits.

Modeling, monitoring and control strategies for high temperature short time pasteurization systems — 1. Empirical model development

Abstract Dynamic models of high temperature short time (HTST) pasteurization systems can be developed by using empirical model development paradigms such as transfer functions and times series models. Properly designed experiments that excite all output variables provide good data that enable the development of accurate dynamic models. These models are used in feedback control and statistical process monitoring system design. The methodology for time series model development for HTST pasteurization processes is illustrated by using data collected from a pilot scale HTST pasteurization system.

Determination of benzene residues in recycled polyethylene terephthalate (PETE) by dynamic headspace‐gas chromatography

A dynamic headspace-gas chromatography (HS/GC) method was developed to quantitate benzene in recycled PETE material derived from 21 PETE beverage bottles. The analytical system consisted of a purge-and-trap apparatus which was interfaced directly with a gas chromatograph/flame ionization detector. Cryofocusing and non-cryofocusing GC systems were used. The technique was applied to spiked PETE test samples which were prepared at various benzene concentrations ranging from 100 ppb to 117 ppm. The initial spiked benzene concentration in the PETE test samples was determined gravimetrically. The HS/GC technique was limited by the slow desorption rate of benzene from the PETE matrix; as a result, multipurges were performed at 60 degrees C. Regression analysis was done on the multipurge data to develop a desorption model which would predict the total amount of benzene in the PETE. The calculated results agreed with the experimental recoveries within +/- 10%. Recovery depended on the initial benzene level in the PETE and ranged from 70 to 90% after the first five purges.

Reduced-Fat Cheese: Regulations and Definitions

On January 6, 1993, the Food and Drug Administration published new rules that amended its food labeling regulations to establish definitions and criteria for the use of specific nutrient content claims (or descriptors) on food labels such as “free,” “low,” “reduced,” “light” or “lite,” and “less.” The agency also established a new General Standard of Identity which permits the use of such nutrient content claims on labels of standardized foods that have been specifically formulated to achieve a nutrition goal, for example, a reduced-fat form of a standardized cheese. Use of a nutrient content claim such as “reduced fat” on a cheese label will require that the product conform to the definition of “reduced” and also to the new general standard of identity. Products which do not have a nutrient content claim shall comply with the specific varietal or class standard of identity for that traditional product, (e.g., cheddar cheese standard).