Certified Food Safety Center, Inc.

Types of Non-Thermal Process Validation

Pulsed Electrical Fields

A pulsed electric field is very high intensity variable electric field through which the food is passed. It is the predominant non-thermal process in use today for acid-based fluids, or fruit juices. Combined with mild heating, it enhances the effectiveness of microbial inactivation and extends shelf life of foods. The pathogens are destroyed through destruction of the cell membranes. Tests have shown anywhere from a five- to nine-log reduction.

Ultraviolet

Ultraviolet processing involves the use of radiation from the ultraviolet region of the electromagnetic spectrum for purposes of disinfection. Typically, the wavelength for UV processing ranges from 100 to 400 nm. The germicidal properties of UV irradiation are mainly due to DNA mutations induced through absorption of UV light by DNA molecules. UV may be used in combination with other alternative processing technologies, including various powerful oxidizing agents such as ozone and hydrogen peroxide. UV applications include disinfection of water supplies and food contact surfaces with microbial load reduction in fruit juices gaining more interest. UV processing has the potential to improve the safety and extend the shelf life of some juices while maintaining more of the fresh-like qualities of the cider compared to thermal processing.

Irradiation

Ionizing Radiation

Radiation for the treatment of food is achieved through the application of gamma rays (with Co-60 or Cesium-137 radioisotope), electron beams (high energy of up to 10 MeV), or X-rays (high energy of up to 5 MeV). Radiation principles explain how the gamma rays, e-beams and X-rays interact with matter. These interactions result in the formation of energetic electrons at random throughout the matter, which cause the formation of energetic molecular ions. These ions may be subject to electron capture and dissociation, as well as rapid rearrangement through ion-molecule reactions, or they may dissociate with time depending on the complexity of the molecular ion. Effects of radiation on matter depend on the type of the radiation and its energy level, as well as the composition, physical state, temperature and the atmospheric environment of the absorbing material. With proper application, irradiation can be an effective means of eliminating and/or reducing the microbial load and thus the foodborne diseases they induce, thereby improving the safety of many foods as well as extending their shelf life.

Cold Plasma

Cold plasma is a novel nonthermal food processing technology that uses energetic, reactive gases to inactivate contaminating microbes on meats, poultry, fruits, and vegetables. A wide array of cold plasma systems that operate at atmospheric pressures or in low pressure treatment chambers are under development. Reductions of greater than 5 logs can be obtained for pathogens such as Salmonella, Escherichia coli O157:H7,Listeria monocytogenes, and Staphylococcus aureus. Effective treatment times can range from 120 s to as little as 3 s, depending on the food treated and the processing conditions. Key limitations for cold plasma are the relatively early state of technology development, the variety and complexity of the necessary equipment, and the largely unexplored impacts of cold plasma treatment on the sensory and nutritional qualities of treated foods.

Supercritical Carbon Dioxide

Supercritical carbon dioxide (SCCO₂) has been found to be a valuable technology for processing and preservation of fruit and vegetables. It has been employed for the inactivation of microorganisms and enzymes in fruit and vegetable products such as juices, purees, and smoothies. SCCO₂ is also an effective and green technology for the extraction of bioactive compounds (carotenoids, flavonoids, phenols, etc.) from fruit and vegetables, owing to the relatively low temperature used and the production of extracts without organic solvents.

Pulsed Light

Pulsed light is a surface irradiation system and not a penetration system. It is primarily useful for surface kill of microorganisms, or for liquids if you can run liquids through as a very thin film. Pulsed light consists of very intense and short flashes of light with wavelengths from UV to NIR, emitted by Xenon discharge lamps. Despite its approval for surface microorganism control in foods by FDA, PL is not yet commercially used, mostly due to the lack of knowledge regarding the critical factors of influence and the inactivation mechanisms.

High Hydrostatic Pressure Processing (HPP)

High hydrostatic pressure processing (also known as high pressure processing (HPP) and ultra-high-pressure processing (UHP) is a method of food processing in which foods are treated under high pressure (up to 6000 atm) to achieve microbial inactivation. Typically, the food product is packaged into flexible containers which are then placed into a high pressure chamber filled with a pressure-transmitting medium (usually water). The fluid filled chamber is then pressurized with the pressure being transmitted through the package and into the food itself. Because HPP causes minimal changes in the freshness characteristics of foods by eliminating thermal degradation, HPP results in foods with a fresher flavor profile and better appearance, texture, and nutrition compared to thermally processed products.

Radio Frequency and Microwave

Microwave and radio frequency heating refers to the use of electromagnetic waves of certain frequencies to generate heat in a material. Microwave and radio frequency heating for pasteurization and sterilization are preferred to the conventional heating for the primary reason that they are rapid and therefore require less time to come up to the desired process temperature. This is particularly true for solid and semi-solid foods that depend on the slow thermal diffusion process in conventional heating. They can approach the benefits of high temperature-short time processing whereby bacterial destruction is achieved, but thermal degradation of the desired components is reduced. Other advantages of microwave and radio frequency heating systems are that they can be turned on or off instantly and the product can be pasteurized after being packaged. Microwave and radio frequency processing systems can also be more energy efficient.

Ultrasound

Presently, most developments of ultrasound (sonication) for food applications are non-microbial in nature. High frequencies in the range of 0.1 to 20 MHz, pulsed operation and low power levels (100 mW) are used for nondestructive testing. Ultrasonic excitation is being examined for nondestructive evaluation of the internal quality and latent defects of whole fruits and vegetables in a manner similar to the use of ultrasound for viewing the developing fetus in a mother’s womb.

The bactericidal effect of ultrasound is generally attributed to intracellular cavitation. It is proposed that micro-mechanical shocks are created by making and breaking microscopic bubbles induced by fluctuating pressures under the ultrasonic process. These shocks disrupt cellular structural and functional components up to the point of cell lysis. Most applications of ultrasound involve its use in combination with other preservation methods.