HPP inactivates microorganisms and enzymes by applying extreme pressure rather than heat. This makes it one of the most commercially successful emerging preservation technologies, already widely used for products like juices, guacamole, and ready-to-eat meats (sliced ham, turkey).

Here's how it works: food is sealed in flexible packaging and placed inside a pressure vessel filled with a liquid medium (usually water). Pressure ranging from 100 to 1000 MPa is then applied. Because pressure transmits uniformly and instantaneously through the liquid, every part of the food receives the same treatment regardless of size or shape. This is a major advantage over heat-based methods, where the center of a food item heats more slowly than the surface.

Key advantages of HPP:

Minimal impact on sensory and nutritional properties (color, flavor, and vitamins are largely preserved)
No need for chemical additives or preservatives
Foods can be processed already in their final packaging
Effective against vegetative bacteria, yeasts, and molds

One limitation worth knowing: HPP is generally less effective against bacterial spores at moderate pressures, which is why it's most commonly applied to refrigerated, not shelf-stable, products.

Pulsed Electric Field (PEF) and Ultrasound

Pulsed Electric Field (PEF) works by placing food between two electrodes and delivering short bursts of high-voltage electricity. These pulses cause electroporation, where the electric field creates permanent pores in microbial cell membranes, leading to cell death. PEF is best suited for liquid and semi-liquid foods such as fruit juices, milk, yogurt, and soups, since the food needs to flow between the electrodes.

Ultrasound uses high-frequency sound waves (above 20 kHz) to generate cavitation bubbles in the liquid portion of food. When these tiny bubbles collapse, they produce intense localized temperatures and pressures that physically disrupt microbial cell membranes. Ultrasound can be combined with heat (thermosonication) or pressure (manosonication) for stronger antimicrobial effects than any single method alone.

Both PEF and ultrasound share the advantage of short processing times and relatively low bulk temperatures, which helps preserve heat-sensitive nutrients and flavors.

High Pressure Processing (HPP), Frontiers | Applications of High and Ultra High Pressure Homogenization for Food Safety

Cold Plasma

Cold plasma is an ionized gas containing a mix of electrons, ions, free radicals, and neutral particles. It's generated by applying electrical energy to a gas (often air, nitrogen, or helium). The reactive species in the plasma interact with microbial cell components, causing oxidative damage that leads to cell death.

Cold plasma can be applied in two ways:

Directly, where the plasma contacts the food surface
Indirectly, where plasma-activated air or water is introduced into a sealed package

It's effective against a broad range of microorganisms, including bacteria, yeasts, and molds. Processing temperatures stay low and treatment times are short (often seconds to minutes), so food quality is largely unaffected. This technology is still mostly at the research and pilot stage but shows strong potential for surface decontamination of fresh produce and packaged foods.

Non-Thermal Preservation

High Pressure Processing (HPP), Food Preservation | Boundless Microbiology

Ultraviolet (UV) Light

UV-C light, in the wavelength range of 200 to 280 nm, inactivates microorganisms by directly damaging their DNA, which prevents them from reproducing. It's effective against bacteria, viruses, and some molds and yeasts.

The main limitation is penetration depth. UV light only treats what it can reach, so it works on surfaces but can't penetrate deep into solid foods. This makes it best suited for:

Surface decontamination of fruits, vegetables, and meats
Treating clear or thin-film liquids (water, juices, liquid egg products)
Sanitizing packaging materials and processing equipment

UV treatment requires no chemicals, leaves no residue, and adds no heat, which makes it a clean and simple complement to other preservation methods.

Ozone Treatment and Edible Coatings

Ozone ( $O_3$ ) is a strong oxidizing agent that destroys microorganisms by disrupting their cell membranes and oxidizing internal cellular components. It can be applied as a gas or dissolved in water (ozonated water). Common applications include sanitizing food contact surfaces, processing equipment, and packaging materials. Ozone breaks down quickly into ordinary oxygen, leaving no chemical residue on treated foods.

Edible coatings take a different approach. Instead of killing microorganisms, they create a thin protective barrier on the food surface. These coatings can be formulated from:

Proteins (whey, casein, soy protein)
Polysaccharides (chitosan, alginate, pectin)
Lipids (waxes, fatty acids)

The coating acts as a barrier to moisture loss, oxygen exposure, and microbial contamination. Coatings can also serve as carriers for antimicrobial agents like essential oils or bacteriocins, adding an active preservation function on top of the physical barrier. This makes edible coatings especially useful for extending the shelf life of fresh fruits, vegetables, and cheese.