Adapting High Hydrostatic Pressure (HPP) for Food Processing Operations (eBook)

Tatiana Koutchma (Autor)

eBook Download: EPUB

2014 | 1. Auflage
78 Seiten
Elsevier Science (Verlag)
978-0-12-420099-9 (ISBN)

Infos

Adapting High Hydrostatic Pressure (HPP) for Food Processing Operations presents commercial benefits of HPP technology for specific processing operations in the food industry, including raw and ready-to-eat (RTE) meat processing, dairy and seafood products, drinks and beverages, and other emerging processes. The book presents high hydrostatic pressure processing (HPP) for treatment of different groups of raw and finished products, focusing on specific pressure-induced effects that will lead to different biological impacts, and the information necessary for specifying HPP process and equipment. It also discusses phenomena of compression heating, the HPP in-container principle, requirements for plastic materials, factors affecting efficacy of HPP treatments, and available commercial systems. Additionally, the book provides updated information on the regulatory status of HPP technology around the world. This book is an ideal concise resource for food process engineers, food technologists, product developers, federal and state regulators, equipment manufacturers, graduate students, and educators involved in research and development. - Includes case studies for HPP treatment of commercially produced foods with information regarding different HPP processing equipment - Gives examples of specific applications for meat and poultry products treatments, fresh juices and beverages, and seafood - Covers energy savings, environmental aspects of HPP technology, and regulatory status

Dr. Tatiana Koutchma is a Research Scientist at the Agriculture and Agri-Food Canada, Guelph Research and Development Centre and a member of the Graduate Faculty at the University of Guelph. Tatiana's research focuses on the application of novel processing technologies to enhance microbial safety, quality and functionality of foods and feed, addresses issues of chemical safety including regulatory approvals, validation and technology transfer. Dr. Koutchma initiates, directs and performs integrated fundamental and applied research, interacts extensively with international government agencies, and collaborates with industry and academia partners. She is an Associate Editor of several international journals, and a co-founder and chair of UV for Food Working Group of International UV Association (IUVA). As well as delivering training for industry and government professionals, she has authored and co-authored 6 books, 14 book chapters, and more than 100 publications in peer reviewed and trade journals.

Textauszug

Chapter 4

HPP Cycles

The section is focused on HPP process parameters for operations of pasteurization and sterilization. The differences in HPP cycles are discussed. The definitions of HPP parameters are given with the detailed effects of the critical product parameters and ranges of their variations. The impact, importance of proper documentation, and control in regards to HPP efficacy is discussed.

Keywords

pressure cycles; HP pasteurization; pressure; temperature; cycle time; critical HP process and product parameters

The section is focused on HPP process parameters for operations of pasteurization and sterilization. The differences in HPP cycles are discussed. The definitions of HPP parameters are given with the detailed effects of the critical product parameters and ranges of their variations. The impact, importance of proper documentation, and control in regards to HPP efficacy is discussed.

HPP utilizes elevated pressures typically in the range of 100–700 MPa with or without addition of external heat.

4.1 High-Pressure Pasteurization

Pasteurization treatment typically employs pressures in the range of 600 MPa (87,000 psi) at or near ambient temperatures (high-pressure–low-temperature process, HT–LT) for a specific holding time. Inactivation of pathogenic vegetative bacteria is the primary objective and product requires refrigeration storage.

Pressure-assisted thermal processing (PATP) or pressure-assisted thermal sterilization (PATS) sterilization treatment use elevated pressures (500–900 MPa) combined with a several minutes heat (90–121°C) exposure at pressure to sterilize low acid foods (high-pressure–high-temperature process, HP–HT). Inactivation of bacterial spores is the primary objective and product normally stored at ambient temperature.

4.2 Process Parameters

Figure 4.1 shows schematically the examples of HPP temperature and pressure cycles during HP–LT and HP–HT processing utilized for pasteurization and sterilization, respectively. The duration of the processing cycle shown in the figure is specific to the design of HP vessel used.

Figure 4.1 HPP temperature and pressure cycles.

When describing the HPP process, the proper documentation of HPP conditions is important and should include the following descriptors.

4.3 Time

Cycle time: The total time for loading, closing the vessel, compression, holding, and decompression and unloading is commonly referred to as the “cycle time.”

Pressure come-up time (CUT): The time required to increase the pressure of the sample from atmospheric pressure to the target process pressure. The CUT depends upon the rate of compression of the sample and pressure-transmitting fluid and is proportional to the power of the pump and flow rate, size of intensifier (gpm), restrictions of high-pressure tubing and valve loss, and the target process pressure.

Decompression time or come-down time (CDT): The time to bring a food sample from process pressure to near atmospheric pressure. The CDT is almost instantaneous. The fast cooling capacity of HPP is of most interest in the production of high-quality foods.

Pressure holding time (HT): The time interval between the end of compression and the beginning of decompression. Commercial processing times, which is the sum of CUT+CDT+HT, can range from a pulse of a few seconds to over 20 min.

The studies of the effects of pressure CUT and holding time, rates of compression, and decompression on the inactivation of pathogenic organisms suspended in different medium suggested that the these HPP parameters should be taken into consideration as a factor affecting microbial inactivation and subsequent storage and carefully documented (Syed et al., 2014). Short cycle times must be targeted since process time has a significant effect on the commercial economics of HPP. A processing time less than 5 min is preferred to maximize productivity and economically justify use of the technology. Obviously, long CUTs will add appreciably to the total processing time and affect the process throughput, but these periods will also affect the inactivation kinetics of microorganisms. Therefore, consistency and control of the CUT, HT, and CDT are important in the development of HPP techniques.

4.4 Pressure

Process pressure (P) refers to the holding pressure during the sample treatment. Due to the system leaks, the pressure drop occurs during hold time. Maximum pressure drop should not be exceeded during HPP operation and needs to be accurately recorded. The pressure achieved and the level of reading accuracy should be identified. It has been recommended to control and record pressure at F 0.5% (electronic) or F 1.0% (dial display) level of accuracy. Further, it is recommended to have at least two methods to measure pressure and have an appropriate periodic calibration program. Frequently, a reference sensor or gauge is sequestered from routine operation and only used in a periodic check mode. Since most HPP users do not have calibration equipment in-house for high pressure, experienced laboratories should perform the calibration of any reference device

Pressure pulsing: Treatment by the application of two or more pressure pulses. When necessary the number of pulses, interval between pulses, temperature and pressure have to be identified.

4.5 Temperature

Product initial temperature (Ti): The initial temperatures of the product before the commencement of pressurization.

Product process temperature (Tf): The final temperature of the product during the sample treatment.

Process temperature: Temperature of pressure-transmitting fluid (water) during holding time.

Initial temperature of pressure-transmitting fluid and the process vessel must be documented, as they are integral conditions for microbial inactivation. Similar to a thermal process, sufficient equilibrium time (primarily based on dimensions and thermal properties of the test product sample and vessel) should be given to assure that all locations within the pressure vessel and the product are equilibrated within ±0.5°C of the target initial temperature. For heterogeneous food samples, additional care or time may be needed to achieve equilibration. An adequate description of methods used for preheating or controlling the sample temperature before HPP should be provided.

The temperature control includes control of the temperature of the pressurization water from 5°C to 30°C. However, there is no control of the water temperature inside the vessel. The high-pressure vessel does not have any temperature control, and it is at the temperature of the room where it is located.

It has been recognized that high pressures of interest do not influence the type K thermocouple readings at temperatures below 500°C. The reference thermocouple sensor should be located at the cold point or equivalent zone within the pressure vessel and calibrated to an accuracy of F 0.5°C (Farkas and Hoover, 2000). Standard methods and good laboratory practices regarding temperature measurement should be followed.

It is important to consider that all compressible substances change temperature during physical compression and this is an unavoidable thermodynamic effect. In general, the temperature of both the product and the pressure-transmitting fluid may rise by 20–40°C during HPP treatment. Solid metallic materials do not experience significant compression heating. Therefore, the temperature increase may vary in foods with relatively complex compositions (Patazca et al., 2007).

In HPP sterilization, compression heating can be used advantageously to provide heating to the targeted final temperature without the presence of large thermal gradients. The compression of the product produces a consistent and thermodynamically predictable temperature increase. Using the minimum initial temperature, the final temperature is estimated for the final process. For example, for a final process temperature of 110°C at 670 MPa, an initial temperature of 78°C results in a 22°C increase from compression heating.

Preheating, precooling, and temperature equilibration of products are important steps in HPP to achieve the required process temperature. A uniform initial target temperature Ti of the food sample is desirable in order to achieve a uniform temperature increase in a homogeneous food system during compression. If cold spots are present within the food or the food system is not homogeneous, parts of the product will not achieve the target process temperature Tf during pressurization. In other cases, keeping the initial temperature low (~4°C) can assist in avoiding a temperature increase during pressurization, and a precooling step may be required.

Detailed information on CUT, holding time, CDT, medium pressure and temperature, product pressure, and temperature (before, during, or after processing) are usually not provided in the published studies. Sometimes the pressure increasing and/or decreasing rates are given. The effects of HPP process parameters as reported in reviewed literature are summarized in Table 4.1.

Table 4.1

Summary of Effects of Process Parameters on HPP Pasteurization

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Produkt-Details

• Erscheint lt. Verlag: 21.6.2014
• Sprache: englisch
• Themenwelt: Technik ► Lebensmitteltechnologie
• ISBN-10: 0-12-420099-0 / 0124200990
• ISBN-13: 978-0-12-420099-9 / 9780124200999