Radio frequency

From Efficiency Finder
Jump to: navigation, search

Back to EFFICIENCY FINDER OF FOOD INDUSTRY


Radio Frequency Heating


General Information

Overview

The development of radio frequency technologies in the food industry capitalizes on the high development on telecommunications and electricity applications (Cambridge University Press, 2015; Mukherjee, 2015) Radio frequency is defined as electromagnetic frequency between 300 KHz to 300 MHz. The difference between RF and Microwave radiation is in the way of transferring energy affecting different profiles of molecules (Orsat & Raghavan; 2014).


Advantages

  • Rapid processing. The processing temperature is reached faster than in conventional processes.
  • Combination with conventional heating can enhance the heating homogeneity.
  • The long length of the waves improve the homogeneity in the heating of the material.
  • It acts as a moisture leveling process.
  • Good energy efficiency.
  • No surface over drying or overheating.
  • Low maintenance cost.
  • The technology combined with conventional methods can lead to meet the quality requirements of products (and often exceed them) and to open a field for new product development while significantly reducing process time and energy requirements.


Disadvantages

  • Initial investment capital cost is high.
  • The operation is subject to fluctuation in the price of electricity.
  • Skilled labor is required for the tuning.
  • Restriction by law in the use of frequency bands due to the frequencies already use in telecommunications.
  • Installations require individual tuning and specific design.
  • The essential problem is the transfer of the energy from the generator (60% efficient) to the material.

(Orsat & Raghavan; 2014)


Base

  • When using RF, an electric field is developed between the electrodes changing the orientation of polar molecules back and forward facing opposite poles, the friction product of this alternating re orientation produce the heat that raise the temperature of the product. RF works well with large quantities of materials with high ionic activity. The amount of heat generated depend on the frequency level, the square of the applied voltage, the dimensions of the product and the dielectric loss factor (principle of dielectric heating).
  • There are two main mechanisms of polarization of the material: Dipolar polarization in which the polarized molecules realign and Space charge polarization, in which charge carriers migrate due to the effect of the alternating field.
  • The polarization effect is a function of the radiation frequency, the dielectric and electric properties of the material, the viscosity of the medium and the size of the polar particles.
  • The dielectric constant of the heated material is key. It is strongly depended on pressure, temperature and frequency of the alternating field (decrease with increasing frequency because the motion of the molecular dipole cannot keep up with the change in the alternating field).
  • Water is the major absorber in foods, alcohol and sugars have also an important role.

(Orsat & Raghavan; 2014)


Description of techniques

The use of radio frequency technology requires the specification of certain parameters as the dielectric properties of the material to be processed pointing to a specific frequency to be used, the quantity of the material and the moisture leveling (especially for drying). The standardized 50 Ohms technology can illustrate the basic component of the system: the base of this technology is the fixed quartz oscillator with subsequent amplification through a vacuum amplifier. The components are the generator with adjustable power output in a standard load of 50 ohm impedance; standard coaxial lines to carry the RF power; matching boxes using adjustable capacitors or inductors located between the coaxial line and the applicator; online measurement of the incident and the reflected RF powers. Optimal design is found when the air gaps between the electrodes and the product are minimal, the parasitic capacitances are minimal and the feeding of conductors are as short and wide as possible.

(Orsat & Raghavan; 2014)


Changes in process

Cooking

Cooking procedures for meat with appropriate package and container lowered 42% in cooking time in a RF oven with respect to cooking time in a water bath. Quality of RF cooked meat was similar to the quality of water bath cooked meat. Pre-cooked and packaged food can help to deal with the food safety regulations and foodborne illness outbreaks.

The marinade increases the cook yield, moisture content, and tenderness of meat. Addition of supplements may be necessary.

(Kirmaci & Singh, 2012)


Pasteurization

  • The pasteurization process through radiofrequency heating enables time temperature regimes that are milder than conventional heating techniques.
  • Potentially selective killing of microorganisms. Better quality in terms of color and taste.
  • When the heat can be generated faster in the microbial cell than in the medium a lower processing temperature can be achieved. Most microbial cell exhibit a change with the technology, enabling the possibility of oscillation at the point of breaking the elastic limit of the membrane. The heating process has the major pasteurization effects and therefore synergies with conventional thermic treatments are no always recommended.
  • Potential for the avoidance of chemical treatments.
  • For E. Coli, frequencies of 11 to 130 MHz, power of 10 W and 1 min. time of treatment with 98% destruction.

(Orsat & Raghavan; 2014)


Cases:

Inactivation of Escherichia coli K-12 and Listeria innocua in milk using radio frequency (RF) heating

Innovative Food Science & Emerging Technologies, Volume 6, Issue 4, 1 December 2005, Pages 396-402

G.B. Awuah, H.S. Ramaswamy, A. Economides, K. Mallikarjunan


Drying

The use of the technology has its major advantage on the generation of heat within the product. High potential for targeting the remaining moisture in post baking products as cookies, crackers and pasta.

(Orsat & Raghavan; 2014)


Thawing

Food thawing assisted by RF heating is faster than conventional thawing. Hot spots can be a major disadvantage of a RF thawing system. Optimization methods can help designing better RF system for thawing purposes.

(Uyar et all, 2015)


Case:

Radio-frequency thawing of food products – A computational study

(Uyar et al, 2015)


Washing products

The technology can be used for product disinfestation, to control product pests in various agri-food items such as cherries, walnuts, almonds, stored grains and fresh fruits.

RF heating uniformity can be improved by forced hot air and mixing. The quality of products is not affected by the RF treatments. RF heating provides effective and physical methods for disinfesting agri-food items.

(Hou & Wang, 2014)


  • Use 4.75 MHz to eradicate pine wood decay fungi with a temperature range of 75-90 °C and 4-12 min. time treatment.
  • Improvement on disinfection of legumes from almost 300 min. to less than 10 min with 27 MHz.

(Orsat & Raghavan; 2014)


Case:

Development of thermal treatment protocol for disinfesting chestnuts using radio frequency energy

(Hou & Wang, 2014)


Energy Savings

Higher energy use due to the minimizing of processing time.


Change in Energy Distribution

Change thermal energy for electricity.


References

  • Cambridge University Press (2015) International Journal of Microwave and Wireless Technologies, Available at: http://journals.cambridge.org/action/displayJournal?jid=MRF (Accessed: 14th March 2015).
  • Hou, L., Ling, B., Wang, S. (2014) 'Development of thermal treatment protocol for disinfesting chestnuts using radio frequency energy', Postharvest Biology and Technology, 98(December), pp. 65-71.
  • Kirmaci, B., Singh, R. (2012) 'Quality of chicken breast meat cooked in a pilot-scale radio frequency oven', Innovative Food Science & Emerging Technologies, 14(April), pp. 77-84.
  • Orsat, V., Raghavan V. (2014) 'Part IV: Alternative thermal processing: Radio Frequency Processing', in Sun, D. (ed.)Emerging Tehcnologies for Food Processing. UK: Academic Press, pp. 385-398.
  • Uyar, R., Bedane, T., Erdogdu, F., Palazoglu, T., Farag, K., Marra, F. (2015) 'Radio-frequency thawing of food products – A computational study', Journal of Food Engineering, 146(February), pp. 163-171.



Back to EFFICIENCY FINDER OF FOOD INDUSTRY