Non-Thermal and Emerging Processing Technologies
1. Emerging food processing technologies
Emerging food-processing technologies are developed to improve food safety, shelf life, quality, nutritional retention, and processing efficiency while reducing undesirable effects associated with conventional processing. Examples include high-pressure processing, pulsed electric fields, pulsed light, ultrasound, irradiation, ohmic heating, dielectric heating, and advanced membrane processes.
2. Major emerging technologies
Important technologies include high-pressure processing (HPP), pulsed electric fields (PEF), ultraviolet processing, pulsed light, power ultrasound, ionizing irradiation, ohmic heating, radio-frequency heating, microwave processing, cold plasma, and membrane-based separation processes. Their suitability depends strongly on the food matrix and intended application.
3. High-Pressure Processing (HPP)
HPP subjects packaged or unpackaged food to very high hydrostatic pressure, commonly within the range used for commercial food applications of several hundred megapascals. The treatment can inactivate many vegetative microorganisms while retaining many fresh-like sensory attributes.
4. Principles of HPP
HPP is commonly explained using Le Chatelier’s principle, the isostatic principle, and the principle of microscopic ordering. Pressure effects depend on the food composition, treatment pressure, temperature, holding time, and target microorganism.
5. Effect of pressure on microbial cells
High pressure can alter cellular membranes, proteins, enzymes, and other cellular structures. Pressure-induced membrane damage and disruption of cellular functions can contribute to microbial inactivation.
6. Applications of HPP
HPP is applied to products such as fruit and vegetable products, juices, ready-to-eat foods, meat products, seafood, dips, sauces, and other packaged foods. Its effectiveness is product- and process-dependent.
7. Pulsed Electric Field (PEF)
PEF processing exposes suitable foods, particularly pumpable liquids and semi-liquid products, to short-duration, high-intensity electric pulses. It is considered a non-thermal or minimally thermal technology when the process is designed to limit temperature rise.
8. PEF treatment parameters
Important PEF variables include electric-field strength, pulse duration, pulse shape, number of pulses, treatment temperature, product conductivity, and residence time. Reported field strengths vary substantially among systems and applications.
9. Microbial inactivation by PEF
The principal mechanism of PEF microbial inactivation is electroporation, in which an electric field increases membrane permeability and can produce irreversible membrane damage at sufficiently severe treatment conditions.
10. Applications of PEF
PEF has been investigated and applied particularly to liquid foods and beverages, including fruit juices and other pumpable products. It is also used to modify plant tissues and assist processes such as extraction and drying.
11. Pulsed light processing
Pulsed light uses intense, short-duration flashes of broad-spectrum light to reduce microorganisms on suitable food, packaging, and food-contact surfaces. Its effectiveness is strongly influenced by surface characteristics and optical properties.
12. Mechanism of pulsed light
Microbial inactivation by pulsed light involves photochemical, photothermal, and photophysical effects. UV components can damage microbial DNA, while the intense energy of the pulse can produce additional cellular damage.
13. Surface applications of pulsed light
Pulsed light is particularly suitable for surfaces, packaging materials, and relatively transparent or optically accessible products because penetration into opaque or highly absorbing foods is limited.
14. Ultraviolet processing
Ultraviolet processing uses electromagnetic radiation, particularly UV-C wavelengths, to reduce microorganisms on exposed food, water, air, equipment, and food-contact surfaces. UV effectiveness depends on dose, exposure geometry, microbial resistance, and product properties.
15. UV microbial inactivation
UV radiation can produce photochemical damage to microbial nucleic acids, particularly through formation of DNA lesions that interfere with replication and transcription.
16. Power ultrasound
Power ultrasound uses high-intensity acoustic energy, generally at frequencies above the audible range, to modify food materials or assist processing operations.
17. Cavitation in ultrasound
A major mechanism of power ultrasound is acoustic cavitation, involving the formation, growth, and collapse of microscopic bubbles. The resulting localized physical forces can influence microbial cells, mass transfer, extraction, and tissue structure.
18. Applications of ultrasound
Power ultrasound can assist extraction, emulsification, crystallization, drying, degassing, cleaning, and selected microbial-processing applications. Its effects depend on frequency, intensity, treatment time, temperature, and food composition.
19. High-voltage electrical discharge
High-voltage electrical discharge uses rapid electrical discharges in a treatment medium to generate intense physical effects. The technology has been investigated for microbial inactivation and other processing applications, particularly in liquid systems.
20. Electrical discharge effects
Microbial inactivation during electrical-discharge processing may involve shock waves, reactive species, localized heating, and mechanical disruption. The relative contribution depends on the equipment and treatment conditions.
Electromagnetic and Radiation-Based Technologies
21. Oscillating magnetic fields
Oscillating magnetic-field processing has been investigated as a potential non-thermal technology. Proposed mechanisms include effects on cellular structures and biochemical processes, but microbial-inactivation results remain dependent on treatment conditions and system design.
22. Food irradiation
Food irradiation uses ionizing radiation to reduce microorganisms, control insects and parasites, delay sprouting, and extend the storage life of selected foods.
23. Approved irradiation sources
Food irradiation systems can use gamma radiation from approved radioisotope sources, electron beams, and X-rays, subject to applicable national regulations and authorized applications.
24. Gray as a radiation unit
The gray (Gy) is the SI unit of absorbed radiation dose and equals one joule of ionizing-radiation energy absorbed per kilogram of material.
25. Factors affecting absorbed dose
Radiation dose distribution depends on factors such as product density, thickness, geometry, composition, radiation source, and processing configuration.
26. Mechanism of irradiation
Ionizing radiation can damage microbial DNA directly and indirectly through the formation of reactive chemical species. Sufficient damage can prevent microbial replication.
27. Applications of food irradiation
Irradiation can be used for applications such as insect control, sprout inhibition in bulbs and tubers, reduction of microbial loads, and treatment of selected foods to improve storage stability. The permitted application and dose depend on the jurisdiction and food category.
28. Dosimetry
Dosimetry is used to determine and verify the radiation dose delivered to a food product. Appropriate reference or calibrated dosimeters are essential for process control and validation.
29. Irradiated food
Irradiated food is food that has been treated with ionizing radiation under controlled conditions. Irradiation does not make food radioactive when approved irradiation processes and sources are properly used.
30. Electromagnetic radiation
Electromagnetic radiation is characterized by wavelength, frequency, and photon energy. Radio-frequency, microwave, infrared, ultraviolet, X-ray, and gamma radiation occupy different regions of the electromagnetic spectrum.
Ohmic, Radio-Frequency and Microwave Processing
31. Ohmic heating
Ohmic heating is a direct electrical-resistance heating method in which an alternating electrical current passes through a food and generates heat within the product.
32. Principle of ohmic heating
The heating effect in ohmic processing is based on the Joule effect. Electrical energy is converted into thermal energy within the food according to its electrical properties.
33. Electrical conductivity in ohmic processing
Electrical conductivity is a major parameter controlling ohmic-heating behavior. It varies with temperature, moisture content, ionic composition, concentration, and food structure.
34. Applications of ohmic heating
Ohmic heating can be used for heating, pasteurization, sterilization, blanching, evaporation, and other processes involving suitable electrically conductive food systems.
35. Radio-frequency heating
Radio-frequency (RF) heating uses alternating electromagnetic fields at radio frequencies to generate heat within food materials through dielectric losses.
36. RF versus PEF
In RF heating, the electromagnetic field is generally applied as a continuous or alternating field for dielectric heating, whereas PEF uses short high-voltage electrical pulses primarily to induce electroporation.
37. Factors affecting RF heating
RF heating is influenced by electric-field strength, frequency, dielectric properties, moisture content, temperature, product geometry, and treatment time.
38. Microwave heating
Microwave heating is a form of dielectric heating in which electromagnetic energy causes molecular polarization and ionic movement, producing heat within the food.
39. Microwave-assisted drying
Microwave-assisted drying can accelerate moisture removal because energy is generated volumetrically within the product. Vacuum conditions can further reduce boiling temperature and assist drying of heat-sensitive products.
40. Dielectric heating
Dielectric heating refers to heating produced by electromagnetic fields interacting with polar molecules and ions in a material. Radio-frequency and microwave heating are major forms of dielectric heating.
Advanced Drying and Ultrasound-Assisted Processing
41. Microwave-vacuum drying
Microwave-vacuum drying combines microwave energy with reduced pressure. Water can evaporate at lower temperatures under vacuum, while microwave energy provides internal heating and can accelerate moisture removal.
42. Ultrasound-assisted drying
Power ultrasound can enhance drying by improving mass transfer and reducing external resistance to moisture movement. It may allow faster drying under selected conditions, although the outcome depends on the food and process design.
43. Ultrasound-assisted extraction
Ultrasound can enhance extraction by promoting cavitation, disruption of plant tissues, and improved solvent penetration. It is used to assist recovery of pigments, phenolic compounds, flavours, oils, and other valuable food components.
44. Acoustic streaming
Acoustic streaming is a fluid flow generated by high-intensity acoustic fields. It can improve mixing and mass transfer during ultrasound-assisted processing.
45. Tempering
Tempering is a controlled temperature-conditioning step in which a frozen product is partially thawed or brought to a specified temperature range before further processing. The exact endpoint depends on the product and process.
Membrane and Integrated Processing
46. Membrane processing
Food membrane processes use selective membranes to separate or concentrate food components. Major processes include microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.
47. Microfiltration
Microfiltration uses relatively large membrane pores to separate suspended particles, microorganisms, and other larger components from liquids. It is used in applications such as clarification and microbial reduction.
48. Ultrafiltration
Ultrafiltration separates components primarily according to molecular size and membrane characteristics. It is widely used for protein concentration, dairy processing, clarification, and fractionation.
49. Nanofiltration and reverse osmosis
Nanofiltration provides selective separation of smaller solutes and ions, whereas reverse osmosis uses a dense membrane and pressure greater than the osmotic pressure to remove water from solutions and concentrate dissolved components.
50. Membrane fouling and integrated membrane systems
Membrane fouling occurs when particles, proteins, microorganisms, colloids, or other substances accumulate on or within a membrane, reducing flux and separation performance. Integrated membrane systems can combine processes such as microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and other membrane operations to improve separation efficiency and product recovery.