Preservation of foods by high pressure

Overview

Treatment with high pressure (HPP: High Pressure Processing), also known as "Pascalisation" is a process that involves applying pressure on a liquid in which the product of interest is submerged. This pressure can reach 6000 times the atmospheric pressure .

The high pressure treatment of food is also called "cold pasteurization." It will extend the shelf life of foods while maintaining their nutritional and organoleptic essential.

The many benefits of this process have been praised and referred to a deterioration of the bacterial flora, no modification of vitamins, a small change of the color and taste. This treatment is therefore an alternative to thermal pasteurization process.

Pressure definition

Where the force exerted on a surface, the effect caused by the expression ratio of the intensity of this force per unit area. This quotient is called the pressure.

Pressure (Pascal) = Force (in Newtons) / area (m²)

In the International System of Units (SI), pressure is expressed in Pascal (Pa): 1 Pa = 1 Nm^-2. There are other units of pressure, the most common being the atmosphere (atm), bar and "millimeter of mercury."

At sea level, the average pressure is equal to 760 mmHg, or 1013 millibars (mbar): this represents the atmospheric pressure. This pressure decreases with altitude.

The history of high pressure

Although the initial studies demonstrating the efficacy of treatment of food by high pressure in the late nineteenth century (the work of Regnard in 1884, Roger Hite in 1885 and in 1899), the first food pascalisés could not see days in 1990 in Japan. He was fairly certain acids such as beverages and jams. The Japanese then pressurized diversified products (fruit juice, meat, fish, rice cakes, ham and beef, sake, etc..) And the range of processing machinery.

Thereafter the process has exceeded the boundaries of Japan and other countries have embarked on this new technology. In 2001, the European Commission authorized the placing on the market of preparations pasteurized fruit produced by a treatment pasteurization at high pressure (Decision 2001/424/CE). It saw the emergence of new products: In France, the orange juice freshly squeezed from the Ulti-Fruit company Pernod Ricard and Spain, sliced cooked ham sold pressurized by society Espuña.

In America, we also saw the emergence of certain products such as pressurized guacamole sold by Avomex and raw oysters to Motivate.

Conservation through the high pressure is now represented on almost every continent, but the advance of Japanese remains undeniable. It is no longer considered "fashionable" but as a process that really belong in the food industry .

The high pressures and food conservation

The effect of high pressure on the preservation of foods is mainly due to the change in the structure of cell components, including proteins and cell membranes.

The tertiary structure of proteins is modified for pressures beyond 200 MPa. Above this value, it is essentially the quaternary structure of proteins that is affected. The direct consequence of protein denaturation is the loss of their biological activities.

The high pressures also induce changes in cell membranes, which are a major cause of bacterial mortality, morphology of cells leading to cell elongation, loss of movement for microorganisms destined to move and some bursts of intracellular vacuoles.

The pressure also plays a role in the availability of energy within cells because it affects the biochemical reactions responsible for producing energy. It may also affect certain molecular reactions such as gene expression and protein synthesis between 30 and 50 MPa.

Effect of high pressure on microorganisms

Various studies have shown that high pressures are able to destroy most micro-organisms. But it depends on the amplitude of the pressure, his time of application, its mode of application (continuous or broken), the pH of the medium, the type of micro-organisms and the temperature of treatment (positive or negative).

Treatment with high pressure makes it possible to pasteurize products at low temperature, and thereby increase their shelf life (shelf-life), while retaining their characteristics, making them close to fresh produce. The optimization of this process can also be done by combined treatment (pressure-temperature-pressure pH, etc.)..

The kinetics of destruction of microorganisms by high pressure can generally be expressed by the following formula:

Log (N) = Log (N₀) - (t / D₁₀)

N₀: initial number of microorganisms.
N: Number of microorganisms surviving after pressurization.
t: time of treatment
D₁₀:Time needed for a given pressure for a 90% reduction in the number of microorganisms present.

Figure 3 gives an example of the destruction kinetics of Listeria monocytogenes under various pressures.

In general, microorganisms resistant to temperature are also resistant to the pressure: The yeasts and molds are less resistant than bacteria, the spore forms are more resistant than vegetative forms and Gram + bacteria are more resistant than the Gram -. In addition, the presence of sugars and proteins on the outer surface of cells increases the resistance of micro-organisms respond to high pressure.

Yeasts and molds are inactivated by pressures between 200 and 300 MPa. Most of the spores of yeast or mold is easily inactivated by a pressure of 400 MPa.

Most bacteria in vegetative form are inactivated by pressures between 400 and 600 MPa. As against bacterial spores can withstand pressures exceeding 1000 MPa. However, treatment between 50 and 300 MPa can induce spore germination. Thus, the process to minimize the survival of spores is a first moderate pressure for germination and a second much more important for inactivation.

Effect of high pressure on enzymes

The effect of high pressure on enzymes can be positive or negative. It is positive when the high pressure used to deactivate enzymes, and it is negative when high pressures are enzymes activate instead of deactivate.

The negative effect (activating enzyme) is observed when applying high pressures around 100 MPa. Indeed, this range of high pressure is unable to denature the protein constituent of the enzymes. For it can save against the enzymes and substrates in contact by modifying the membranes that separate them.

The positive effect (deactivation of enzymes) observed when applying high pressures beyond 100 MPa. Indeed, this range of pressure changes the tertiary structure and / or quaternary protein constituent of enzymes, making them inactive.

Techniques pascalisation

The technique of pressurization (or pascalisation) is to apply pressure on a liquid that contains the products to undergo the treatment. Compressibility of the fluid transmitting the pressure is low. Often, the liquid used is water. It is thus derived the name "high hydrostatic pressure.

The product is encased in its sales package (often a flexible and waterproof bag) in which a vacuum was then submerged under water. The pressure applied is isostatic (it is identical in all directions in space) at all points of the enclosure and thus the product. Thus compressed, the product can return to its original shape when pressure is released. The range of high pressures applied vary from a few tens of MPa (mega Pascals) at 1 GPa (Giga Pascal).

This process presents the following advantages:

1. treatment with high pressure occurs at temperatures below 100 ° C and even in general at room temperature
2. This treatment requires much less energy than most other systems of conservation
3. there is no pressure gradient in the product because the transmission of this pressure is instantly as opposed to a heat treatment.

The equipment consists of an enclosure resistant to pressure, a circuit of "high pressure", an external pump compression of the fluid, a control unit and a device for heating or cooling.
Two types of cuts are currently available: compression "direct" and "indirect".

Direct compression

In the compression system "direct" (Figure 5), pressure is generated directly inside the chamber by the compression of a piston on the community in touch. The fluid and the pressure vector, comes under low pressure in the enclosure, and then allows the plunger to generate pressure. The advantage of this method is to quickly reach high pressures, but it remains limited to speaker of small diameter because of sealing problems.

Indirect compression

The second possibility is compression "indirect." In this case, a pump "high pressure" sends a fluid pressure in an enclosed space (Figure 6). This method is most widespread in industry.

Application process in the food industry

The use of high pressure is an alternative to conventional thermal treatment to destroy micro-organisms. This process will extend the storage stability of products while maintaining the nutritional and sensory properties of food.

Regulatory

European legislation on products treated with high pressure in the food industry is based on the EC Regulation 258/97, which entered into force on 15 May 1997. It brought, before any sale, a permission marketing in the European Union for new foods and new ingredients. Products treated with high pressure are considered as such. This approach is mandatory for all member states.

In the United States, regulation is more favorable to the development of "new products". The two departments responsible for marketing approval of the product are: the FDA (Food and Drug Administration) and FSIS (Food Safety and Inspection Service). The FDA allows marketing but denies any responsibility, the industry is solely responsible. The FSIS is simply asking that treatment with high pressure is able to kill Listeria monocytogenes in cooked dishes or the products ready to eat meat or poultry.

Potential risks of high pressure process

There is as yet no study that shows toxicity of food products treated by high pressure. It is known that high pressure affects protein structure, activity of some enzymes and certain molecular bonds. It would be necessary to compile all data on the effects of high pressure to clarify their roles to the toxicity, allergenicity, digestibility loss and alteration of the nutritional qualities.