Introduction

22.2.1.1 Definition and Historical Perspective

Historically, applications of HPP for the preservation of foods were first conducted by Bert Hite who adapted high-pressure processing to a variety of foods and beverages in the late 1890s and early 20th century [2,3]. From Hite's work until the 1980s, only scattered attempts were made to investigate the potential commercial application of HPP to foods. With the sustained demand for high-quality foods that are minimally processed and additive-free in developed countries, HPP has attracted interest from research institutions, food companies, and regulatory agencies over the last two decades in the pursuit of producing better quality foods more economically.

HPP subjects foods to pressures between 100 and 800 MPa with exposure times ranging from a millisecond pulse to over 20 minutes, although most commercial treatments times are 7 minutes or preferably less [4,5]. The temperatures of products and media during pressure processing can be below 0°C or above 100°C, depending on the product requirements; however, current commercial HPP uses ambient temperatures.

The first commercialized food product employing pressure preservation was fruit preserves marketed in Japan in 1991. These pressure-treated jams and jellies continue to be sold in Japan in addition to salad dressings and a wide range of fruit juices. Pressure-treated guacamole successfully entered the U.S. marketplace in 2001, followed by HPP salsa. These products have been available nationwide, but pressurized guacamole and salsa remain most popular in the southwestern region of the U.S. In 2004 it is anticipated that pressure-processed chopped onions will be sold as an ingredient in premium salad dressings. This onion product will be available in fresh chopped form months after the normal season ends. They will be available in 8 oz stand-up, resealable bags and as 2.5 lb pouches for club and superstores. The intended refrigerated shelf life is 45 days, but 90 days of storage has been demonstrated without detrimental quality changes. Pressure-processed chopped onions are said to have a "sweeter taste that isn't bitter, with a fresher, crunchier texture.'' Also anticipated in 2004 from a Canadian venture is applesauce and applesauce/fruit blends packaged as eat-on-the-go single-serve flexible tubes: "Our Way of Preserving Nature,'' and from Mexico, fruit "smoothie" products for North American distribution. This company produces juices, nectars, and bottled drinks.

22.2.1.2 Equipment

Typical HPP equipment usually consists of a pressurized vessel, two end closures at each end of the vessel, a low-pressure pump, an intensifier to generate higher pressures, and system controls. HPP systems can be designed to treat either unpackaged liquid foods semicontinuously or packaged foods in a batch manner. A schematic of a batch HPP system is presented in Figure 22.1.

22.2.1.3 Critical Processing Factors

Critical process factors in HPP include, but are not limited to, treatment pressure, holding time at pressure, come-up time to achieve treatment

Safety Pressure Safety Control Service area access hatch light beam vessel light beam cubicle 9 ft 10 in x 6 ft 7 in (3 m x 2 m)

Switchgear

Safety Pressure Safety Control Service area access hatch light beam vessel light beam cubicle 9 ft 10 in x 6 ft 7 in (3 m x 2 m)

Switchgear

Vessel temperature Water module 25X pump Service area control module

FIGURE 22.1 Fresher Under Pressure high-pressure processing systems (215 L) from Avure Technologies Inc., a wholly owned subsidiary of Flow International Corporation.

Vessel temperature Water module 25X pump Service area control module

FIGURE 22.1 Fresher Under Pressure high-pressure processing systems (215 L) from Avure Technologies Inc., a wholly owned subsidiary of Flow International Corporation.

pressure, decompression time, initial temperature of food products, treatment temperature, the temperature distribution in the vessel at pressure as a result of adiabatic heating, product properties (e.g., pH, composition and water activity, food compressibility), packaging material, and the microbiota of the food [6]. Package size and shape are not critical factors in process determination because pressure acts instantaneously and uniformly throughout the chamber and the food mass. For pulsed pressure processing, additional process factors are pulse shape (i.e., the waveform), frequency, and pulse pressure magnitudes.

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