Pasteurization Unit Research Articles

Investigation of the residence time distribution in a plate heat exchanger with series and parallel arrangements using a non-ideal tracer detection technique

The objective was to study the flow pattern in a plate heat exchanger (PHE) through residence time distribution (RTD) experiments. The tested PHE had flat plates and it was part of a laboratory scale pasteurization unit. Series flow and parallel flow configurations were tested with a variable number of passes and channels per pass. Owing to the small scale of the equipment and the short residence times, it was necessary to take into account the influence of the tracer detection unit on the RTD data. Four theoretical RTD models were adjusted: combined, series combined, generalized convection and axial dispersion. The combined model provided the best fit and it was useful to quantify the active and dead space volumes of the PHE and their dependence on its configuration. Results suggest that the axial dispersion model would present good results for a larger number of passes because of the turbulence associated with the changes of pass. This type of study can be useful to compare the hydraulic performance of different plates or to provide data for the evaluation of heat-induced changes that occur in the processing of heat-sensitive products.

Using Computational Fluid-Dynamics (CFD) for the evaluation of beer pasteurization: effect of orientation of cans

In-package pasteurization is the most used method for beer microbiological stabilization. The search for safer and better quality food has created a need to better understand the processes involved in producing it. However, little is known about the temperature and velocity profiles during the thermal processes of liquid foods in commercial packaging, which results in over-dimensioned processes to guarantee safety, decreasing the sensorial and nutritional characteristics of the product and increasing process costs. Simulations using Computational Fluid-Dynamics (CFD) have been used by various authors to evaluate those processes. The objective of the present paper was to evaluate the effect of packaging orientation in the pasteurization of beer in a commercial aluminum can using CFD. A heating process was simulated at 60 oC up to 15 PUs (a conventional beer process, in which 1 Pasteurization Unit (PU) is equivalent to 1minute at 60 oC). The temperature profile and convection current velocity along the process and the variation of the PUs were evaluated in relation to time considering the cans in the conventional, inverted, and horizontal positions. The temperature and velocity profiles were similar to those presented in the literature. The package position did not result in process improvement.

FDTD MODELING AND SIMULATION OF MICROWAVE HEATING OF IN-SHELL EGGS

Considering microwaves as a viable alternative for the pasteurization of In-shell eggs, preliminary trials performed had conflrmed that microwave at 2450MHz can be successfully used to raise the temperature of in-shell eggs to the required pasteurization temperatures in a few minutes. Based on these trials a flnite difierence time domain (FDTD) model was developed using C language and MATLAB to simulate the E fleld and power distribution in lossy dielectric media like that of the egg components (egg white and yolk) taking into consideration the complex shape, dielectric properties and heterogeneous composition of the in-shell egg. This can be used to assist in the design and development of an industrial microwave in- shell eggs pasteurization unit.

Establishment of Minimum Operational Parameters for a High-Volume Static Chamber Steam Pasteurization System (SPS 400-SC™) for Beef Carcasses to Support HACCP Programs

A static chamber steam pasteurization unit (SPS 400-SC()) was installed in a high-volume commercial beef slaughter facility. The SPS 400-SC consists of a three-phase carcass treatment cycle of water removal, steam pasteurization, and water chilling. Seven chamber temperatures (71.1, 73.9, 76.7, 79.4, 82.2, 85.0, and 87.8 degrees C) were evaluated at the midline area of pre-rigor beef carcasses. For each temperature evaluated, 20 carcass sides were randomly selected and aseptically sampled by tissue excision immediately before and after steam pasteurization to determine total aerobic bacteria, Enterobacteriaceae, generic E. coli, and total coliform populations. The 87.8 and 85.0 degrees C treatment temperatures were highly effective at reducing total aerobic bacterial populations, with log(10) reductions of 1.4 and 1.5 CFU/cm(2), respectively, from pretreatment mean population levels of 1.7 and 1.9 log10 CFU/cm(2). These temperatures also reduced Enterobacteriaceae, total coliforms, and generic E. coli to undetectable levels (<0.4 CFU/cm(2)) on all carcasses sampled. Treatment at 82.2 was marginally effective at reducing bacterial populations, while 71.1, 73.9, 76.7, and 79.4 degrees C treatments were ineffective at reducing microbial populations. In a Hazard Analysis Critical Control Points (HACCP)-based system employing steam pasteurization of carcasses as a critical control point, a critical limit of 85.0 degrees C as a minimum chamber temperature should be established, with a targeted operating temperature of 87.8 degrees C providing optimum antimicrobial activity.

Estimation of fouling in a plate heat exchanger through the application of neural networks

AbstractPasteurization is an important, if not the most important, process step in the packaging of milk. It is subject to alterations stemming from the variation in the temperature, pH and raw milk quality. The variability may manifest itself in changes in the formation of the deposit (fouling) in the pasteurization unit, such that there is a need for tools, both instrumentation and computational, to help in monitoring the process and keeping it on the desired course. In this paper we describe a practical procedure based on artificial neural networks (ANN) that allows prediction of the deposit thickness, the overall heat transfer coefficient and the critical time (the time that the unit has to be stopped for cleaning) for reducing the impact of fouling on such processes. The procedure determines when the cleaning operation is required once the system is under critical conditions of operations. A combination of fundamental studies and plant measurements were used for study of the operating conditions and thus evaluation of the trades‐offs between operating conditions and longer operating life span. The results are encouraging, enough to validate current operating industrial techniques. Copyright © 2005 Society of Chemical Industry

Mycobacterium aviumSubspeciesparatuberculosisCultured from Locally and Commercially Pasteurized Cow's Milk in the Czech Republic

Between November 2002 and April 2003, 244 bottles and cartons of commercially pasteurized cow's milk were obtained at random from retail outlets throughout the Czech Republic. During the same period, samples of raw milk and of milk that was subsequently subjected to a minimum of 71.7 degrees C for 15 s in a local pasteurization unit were also obtained from two dairy herds, designated herds A and B, with low and high levels, respectively, of subclinical Mycobacterium avium subsp. paratuberculosis infection, and from one herd, herd C, without infection. Infection in individual cows in each herd was tested by fecal culturing. Milk samples were brought to the Veterinary Research Institute in Brno, Czech Republic, processed, inoculated onto Herrold's egg yolk slants, and incubated for 32 weeks. Colonies were characterized by morphology, Ziehl-Neelsen staining, mycobactin J dependency, and IS900 PCR results. M. avium subsp. paratuberculosis was cultured from 4 of 244 units (1.6%) of commercially pasteurized retail milk. M. avium subsp. paratuberculosis was also cultured from 2 of 100 (2%) cartons of locally pasteurized milk derived from infected herds A and B and from 0 of 100 cartons of milk from uninfected herd C. Raw milk from 1 of 10 (10%) fecal culture-positive cows in herd A and from 13 of 66 (19.7%) fecal culture-positive cows in herd B was culture positive for M. avium subsp. paratuberculosis. These findings confirm that M. avium subsp. paratuberculosis is present in raw milk from subclinically infected dairy cows. The culture of M. avium subsp. paratuberculosis in the Czech Republic from retail milk that had been pasteurized locally or commercially to the required national and European Union standards is in agreement with similar research on milk destined for consumers in the United Kingdom and the United States and shows that humans are being exposed to this chronic enteric pathogen by this route.

Effectiveness of a Laboratory-Scale Vertical Tower Static Chamber Steam Pasteurization Unit against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria innocua on Prerigor Beef Tissue

A laboratory-scale vertical tower steam pasteurization unit was evaluated to determine the antimicrobial effectiveness of different exposure times (0, 3, 6, 12, and 15 s) and steam chamber temperatures (82.2, 87.8, 93.3, and 98.9°C) against pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria innocua) inoculated onto prerigor beef tissue. Samples were collected and microbiologically analyzed immediately before and after steam treatment to quantify the effectiveness of each time-temperature combination. The 0-s exposure at all chamber temperatures (cold water spray only, no steam treatment) was the experimental control and provided ≤0.3 log CFU/cm2 reductions. Chamber temperatures of 82.2 and 87.8°C were ineffective (P > 0.05) at all exposure times. At 93.3°C, significant reductions (>1.0 log CFU/cm2) were observed at exposure times of ≥6 s, with 15 s providing approximately 1 log cycle greater reductions than 12 s of exposure. The 98.9°C treatment was consistently the most effective, with exposure times of ≥9 s resulting in >3.5 log CFU/cm2 reductions for all pathogens.

Impact of temperature on lethality and energy efficiency of apple juice pasteurization by pulsed electric fields treatment

The applicability of pulsed electric fields as a non-thermal preservation process for liquid food decontamination has been shown in several studies. However, high costs of operation due to the occurrence of a high amount of dissipated electrical energy inhibited an industrial exploitation so far. In this study the focus was put on improving energy efficiency of this process for pasteurization of apple juice inoculated with Escherichia coli by investigating the relation between achieved reduction in survivor count and electric field strength and treatment temperature. An empirical mathematical model was derived to predict the required input of electrical energy for a given inactivation. Using synergistic effects of elevated treatment temperature of 35–65 °C on microbial inactivation the energy consumption could be reduced from above 100 to less than 40 kJ kg −1 for a reduction of 6 log cycles and the need to preheat the juice before treatment provided a possibility to recover the dissipated electrical energy after treatment, leading to a drastic reduction in operation costs. To evaluate the thermal load of the product the pasteurization unit (PU) and the cook value, key benchmarks for the thermal load, were used to compare PEF and conventional heat treatment.

Microbial evaluation of steam pasteurization and comparison of excision versus sponge sampling recovery (1998)

The use of steam pasteurization (SPS400™; Frigoscandia, Bellevue, WA) as a viable commercial-scale intervention method to treat pre-rigor beef carcasses uniformly hasbeen evaluated for temperatures from 180E to 201 ÌŠF. Effectiveness at lower temperatures(minimum atmospheric temperature of 170 ÌŠF) has not been evaluated. Previous studies of steam pasteurization used excision sampling. However, the USDA-FSIS has suggested use of nondestructive sampling of chilled beef carcasses for generic Escherichia coli, so we compared excision and sponge sampling in a commercial slaughter facility. Twenty-eight beef carcasses were monitored to determine the effectiveness of steam pasteurization and to compare the two sampling methods. Total aerobic mesophilic bacteria, E. coli, and coliform counts were all reduced (P≤0.01) by steam pasteurization. Sponge sampling of carcasses for E. coli. provided lower recovery (P≤0.01) than excision sampling. None of 28 carcasses tested positive by sponge sampling; however, six of the same microbial carcasses were positive (0.39-23.6 CFU/cm2) by excision sampling immediately adjacent to the sponged area. The SPS 400™ steam pasteurization unit, operating at a minimum atmospheric temperature of 170 ÌŠF reduced (P≤0.01) all bacterial populations on prerigor beef carcasses. Excision data, compared to previous commercial evaluations of the SPS 400™ at a slightly higher operating atmospheric temperature, provided comparable total reductions, but a few more E. coli survived at 170 F.

Industrial pasteurization of plasma and criteria of quality

The approach followed in the design of a large-scale pasteurization treatment (60 degrees C for 10 hours in the liquid state) of fresh frozen plasma is presented. Various aspects thought to influence the viral safety of such a product are discussed. They are based largely upon the fact that, although it is subjected to a specific viral inactivation treatment, this plasma does not benefit from any fractionation steps known to participate in the potential elimination of infectious agents during the manufacture of plasma derivatives. Consequently, the plasma is obtained from regular plasmapheresis donors, and the plasma donations used to make the pool must be negative for anti-HIV-1 and -2, anti-HCV, anti-HBc, anti-HTLV-1 and -2, HBs antigen and parvovirus B19 antigen, and have a normal level of ALT. The batch size is limited to 100 plasma units to limit the potential infectious risk associated with very large batches, especially if an infectious agent, resistant to pasteurization, is present. Pasteurization has been chosen for this procedure, as applied to plasma derivatives, has been shown to inactivate a broad spectrum of viruses, both enveloped and non-enveloped. The process is relatively simple. The frozen plasma units are opened, and the plasmas are mixed and thawed at 30 degrees C to avoid the formation of cryoprecipitate. The liquid plasma is transferred to a sterilized container and stabilizers are added. The mixture is then transferred to the pasteurization unit to be heat-treated at 60 degrees C for at least 10 hours under gentle mixing. Following cooling, the mixture is ultrafiltered to eliminate the stabilizers and to concentrate the plasma pool to its initial volume. The plasma is sterile-filtered, then dispensed into bottles and frozen. Virus validation of this pasteurization process, carried out by independent virology laboratories, have confirmed the ability of the process to inactivate more than 4 to 6 logs of non-enveloped or enveloped, DNA or RNA, viruses, including HIV-1 and Sindbis virus, in less than 5 hours of heat-treatment. The biological characteristics of the pasteurized plasma include a good preservation (75 to 95%) of the activity of clotting factors, including FI, FV, FVIII, FXI, and FXIII, and protease inhibitors. The overall clottability of the plasma, as expressed by the APTT, is almost unchanged.(ABSTRACT TRUNCATED AT 400 WORDS)

Operating Experiences of Sludge Disinfection and Stabilization at Colburn Sewage Treatment Works, Yorkshire

ABSTRACTA NEW integrated sludge treatment plant was installed at Colburn sewage treatment works (STW) in 1986. The plant comprises a number of novel features including a continuous gravity thickener features including a continuous gravity thickener, a pasteurization unit using submerged combustion of digester gas for sludge heating, a peat‐bed odour control system, and a ‘pump‐our/pump‐in’prefabricated anaerobic digester. Plant operation is controlled automatically by a computer system The performance of the thickener has been in accordance with predictions and has achieved at least a halving of raw sludge volume. The submerged combustion plant has consistently heated the sludge to 70°C with high efficiency of gas utilization before the anaerobic digestion stage. Some problems were experienced with the continuity of supply of the raw sludge but overall the plant has performed very satisfactorily with the production of a high quality disinfected and stabilized sludge for use by local farmers.

Survival of Listeria monocytogenes in milk during high-temperature, short-time pasteurization.

Milk from cows inoculated with Listeria monocytogenes was pooled for 2 to 4 days and then heated at 71.7 to 73.9 degrees C for 16.4 s or at 76.4 to 77.8 degrees C for 15.4 s in a high-temperature, short-time plate heat exchanger pasteurization unit. L. monocytogenes was isolated from milk after heat treatment in six of nine pasteurization trials done at 71.7 to 73.9 degrees C and in none of three trials done at 76.4 to 77.8 degrees C. An average of 1.5 to 9.2 L. monocytogenes cells was seen in each milk polymorphonuclear leukocyte before heat treatment in 11 of 12 pasteurization trials. Noticeable degradation of leukocytes with intracellular listeria was detected in unpasteurized milk after 3 days of storage at 4 degrees C, and by 4 days of storage leukocytes had deteriorated to cellular debris, suggesting that holding unpasteurized milk refrigerated for 4 or more days would eliminate a protective effect leukocytes may provide for increasing heat resistance of L. monocytogenes. Results indicate that under the conditions of this study, L. monocytogenes can survive the minimum high-temperature, short-time treatment (71.7 degrees C, 15 s) required by the U.S. Food and Drug Administration for pasteurizing milk.