According to the Food Safety Modernization Act regulations, any preventive microbial inactivation technology must be validated.[1] It is necessary to identify a suitable nonpathogenic surrogate with a similar or higher heat resistance than that of the target pathogen before thermal inactivation validation because pathogens cannot be used in food processing plants. The safety of low-moisture foods is becoming a major concern after several recent foodborne illness outbreaks.[2] The thermal resistance of bacteria in these foods creates major challenges in developing suitable food safety intervention technologies without deteriorating food quality.
Radiofrequency Heating
Radiofrequency (RF) heating involves utilizing electromagnetic energy at a frequency range of 3 kHz to 300 MHz. Only select RF frequencies (13.56, 27.12, and 40.68 MHz) are permitted for industrial, scientific, and medical applications.[3] RF is widely applied for sterilization/pasteurization,[4–10] thawing,[11,12] disinfestation,[13,14] and drying.[15] The heat is volumetrically generated by rotation and friction of ions and dipolar molecules in food products because of an alternating electrical field. The movement of positive and negative ions is ionic conduction, and rotation of dipolar molecules is dipole rotation.3 Ionic conduction and dipole rotation are the dominant mechanisms of RF heating.
Advantages of RF Heating
RF has a longer wavelength and penetration depth than those of microwaves. Thus, RF heating has advantages of more even electric field distribution and more uniform heating compared with microwave heating.[3] Its longer penetration depths make RF suitable for bulk sample treatment in the food industry. Since RF heating is volumetric, the whole sample can be heated rapidly. In conventional heating, the heat is transferred from the external surface to the internal center of the sample, resulting in longer come-up times to achieve the target temperature at the cold spot. To pasteurize egg white powder, for example, it is traditionally heat-treated by storing packaged product in a hot room at 58–60 °C for 10–14 days.[16] However, it took only 8 hours for RF-assisted processing to achieve pasteurization at 90 °C.[17] The shorter come-up time allows RF heating to be a high-temperature, short-time processing technology, which is more energy efficient and could retain more food quality after treatment. This is the major advantage of RF heating.
Because RF waves vibrate bound water,2 it is a suitable technology for low-moisture foods, such as spices and milk powder, which have more bound than free water.[2,18] RF systems can be turned on/off instantly for better process control. Since most food packages are plastic bags or cardboard boxes that are transparent to RF waves,[13] food products can be pasteurized after being packaged. Although heating uniformity is better in RF than in traditional thermal processing or microwaves, there is still room to improve heating uniformity in RF processing to achieve superior product quality.[3,19–21] Computer simulation is a powerful tool to understand RF heating and improve uniformity.[19–24] Therefore, RF heating has great potential to be applied for low-moisture food pasteurization in the food industry.
Critical Process Control Parameters
RF heating is influenced by many factors, such as the dielectric properties of food products, electrode gap, configurations of the top electrode and package, and top electrode voltage of a free-running oscillator with a two parallel-plate system. Dielectric properties of food products depend on moisture content (MC), frequency, temperature, density, and chemical composition.[3] Among these factors, MC is a major factor that affects the heating rate.[3] The dielectric constant represents a material’s ability to store the electric field energy, and the dielectric loss factor determines how much electromagnetic energy can be converted into heat.[25] Numerous researchers have measured the dielectric properties of different food products.[11,25–29] Top electrode voltage and electrode gap can regulate RF output power.[13,14] Electrical field strength determines the power output of a piece of equipment that impacts the heating rate. Very strong electrical field strength between two electrodes can cause arcing. The configurations of the top electrode and food package influence electric field distribution in the RF cavity, which can be optimized to improve heating uniformity.[22]
SPONSORED CONTENT Radio Frequency Pasteurization:
The Wave of the Future in Food Pasteurization
Founded in 1946, Radio Frequency Company (RFC)’s 40,000 sq. ft. design and manufacturing facility is located in the suburbs of Boston alongside the historic Charles River. RFC is a global manufacturer of advanced industrial radio frequency (RF) processing systems for the rapid heating, drying, disinfestation, and pasteurization of food products and ingredients.
Today, RFC’s Macrowave™ pasteurization systems are treating more than 500 million pounds of food ingredients, both for humans and pets, per year. Unlike irradiation and other treatment methods, RF treatment is certified organic, natural, and can be used on an FDA-approved clean label. In an RF pasteurization system, the RF generator creates an alternating electric field between two electrodes, above and below the system conveyor, which causes the treated product to heat rapidly and uniformly throughout its entire thickness, whether it is processed in bags, or in bulk on a troughed conveyor. This rapid and volumetric heating means that there is no temperature differential from the surface to the center of a product and no prolonged soak time that can damage functionality and other organoleptic qualities. All Macrowave systems meet FSMA standards for a preventive control step and incorporate the HACCP monitoring, data logging, and alarm functionality required for a kill-step validation. Treatment systems are available in a broad range of sizes to suit individual customer requirements and are designed and constructed to GMP standards for food safety and ease of sanitation. All Macrowave systems are UL approved, FCC certified, and EU compliant. For all systems deployed domestically or internationally, RFC maintains a complete spare parts inventory; factory-trained RF service technicians are available 24/7. RFC’s MacroCare Preventive Service Plan assures customers that their system is operating at peak performance, minimizing downtime and maximizing their ROI. Because RF treatment is a USDA Organic thermal process and is easy to own and operate, it’s no wonder why RFC’s Macrowave pasteurization systems are truly “the wave of the future” in food safety.