Consumers demand high quality and convenient products with natural flavor and taste, and greatly appreciate the fresh appearance of minimally processed food. Besides, they look for safe and natural products without additives such as preservatives and humectants.
To overcome all these problems new technologies like High Pressure Processing were needed.
What is High Pressure Processing?
High-pressure processing (IPP) is a non-thermal technique of food preservation that inactivates harmful pathogens and vegetative spoilage microorganisms by using pressure rather than heat to induce a pasteurization effect. HPP employs intense pressure (about 400-600 MPa) at refrigeration or mild process temperatures (< 45°C), preserving most foods with minimal effects on taste, texture, appearance, or nutritional value.
The ability of high pressure to inactivate microorganisms and spoilage catalyzing enzymes, whilst retaining other quality attributes, has encouraged Japanese and American food companies to introduce high pressure processed foods in the market.
History
The fact that “high pressure kills microorganisms and preserves food” was discovered way back in 1899 and has been used with success in chemical, ceramic, carbon allotropy, steel/alloy, composite materials and plastic industries for decades, it was only in late 1980’s that its commercial benefits became available to the food processing industries.
Hite (1899) investigated the application of high pressure as a means of preserving milk, and later extended the study to preserve fruits and vegetables.
It then took almost eighty years for Japan to re-discover the application of high-pressure in food processing. The use of this technology has come about so quickly that it took only three years for two Japanese companies to launch products, which were processed using this technology.
The first products of high-pressure processing were jams and jellies.
Principals of High-Pressure Processing
There are two general scientific principles which are of direct relevance to the use of HP in food processing.
The first of these is Le Chatelier’s principle, which applies to all physical processes and states that when a system at equilibrium is disturbed, the system responds in a way that tends to minimize the disturbance. This means that HP stimulates reactions that result in a decrease in volume but dampens reactions that involve an increase in volume. Any phenomenon (e.g., phase transition, change in molecular configuration, chemical reaction) that is accompanied by a decrease in volume will be enhanced by pressure.
For example
When you open a window in a room filled with a strong-smelling odor, the fresh air rushes in to dilute the smell, minimizing the odor disturbance. Le Chatelier's principle applies increasing the concentration of fresh air (by opening the window) shifts the system towards the side that reduces the concentration of the odor, helping to restore a more pleasant equilibrium.
Second, the isostatic rule states that pressure is instantaneously and uniformly transmitted throughout a sample under pressure, if the sample is in direct contact with the pressure medium or hermetically sealed in a flexible package that transmits pressure. Pressure is transmitted in a uniform (isostatic) and quasi-instantaneous manner throughout the sample; the time necessary for pressure processing is therefore independent of sample size, in contrast to thermal processing.
For example
When you remove the cap, you may hear a hissing sound as the pressure is released. This is because the beverage inside the bottle was sealed under pressure, and when the seal is broken, the pressure is instantaneously and uniformly transmitted throughout the liquid, causing the release of gas and the familiar sound. The isostatic rule ensures that the pressure is evenly distributed throughout the liquid in the bottle.
Components of High-Pressure Processing
The basic components of a HPP system are a pressure vessel, a pressure-transmitting fluid, a material handling pressurizing system, and supporting units such as heating or cooling components.
The most common transmitting fluids are water, food-grade glycol-water solutions, silicone oil, sodium benzoate solutions, ethanol solutions, and castor oil.
Working of High-Pressure Processing
During HPP, the pressure is applied uniformly and simultaneously in all directions. It is called isostatic pressure and it is the reason why food is not crushed during the treatment. This is the major advantage compared to thermal methods where the temperature of product is increased gradually. Once loaded and closed, the vessel is filled with a pressure-transmitting medium. Air is removed from the vessel with an automatic deaeration valve by means of a low-pressure fast-fill-and-drain pump, and high hydrostatic pressure is then generated by direct or indirect compression or by heating the pressure medium.
In biological systems, the changes brought about by the volume-decrease reactions of HPP include denaturation of proteins, gelation, hydrophobic reactions, phase changes in lipids (and, therefore, in cell membranes) and increases in the ionization of dissociable molecules due to electrostriction". The high pressure process is characterized by three parameters: temperature (T), pressure (p) and exposure time (t) when compared heat preservation.
Advantages of using High Pressure processing
inactivation of vegetative bacteria and spores at higher temperatures.
no evident of toxicity.
preservation of nutrients, colors and flavors.
reduced processing times.
uniformity of treatment throughout food.
potential for reduction or elimination of chemical preservatives.
positive consumer appeal.
Disadvantages of using High Pressure Processing
expensive equipment.
foods should have 40% free water for anti-microbial effect.
batch processing.
limited packaging options.
little effect on food enzyme activity.
some microbial survival.
Several aspects of High Pressure Processing will be discussed further
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