Emerging Food Processing Technologies 1

Microwave Heating:

Microwaves, which are a part of the electromagnetic spectrum and have a frequency range between 300 MHz and 300 GHz, have been extensively employed to various food processing such as drying, sterilization, tempering, and cooking because MW heat foods in a rapid and direct manner. Frictional energy resulting from molecular dipole moments and conductive migration of charged ions in the alternating electromagnetic field can instantly generate heating inside food material.

Dielectric properties play a key role in understanding the interaction between electromagnetic fields and the components of foods. Dielectric properties of food products are mainly affected by frequency, temperature, and moisture contents. The domestic microwave oven has become the most useful home appliance owing to simple operation and rapid heating or thawing of “ready to eat” foods.

Radio Frequency Heating:

Similar to Microwave heating, radio frequency heating, which can be classified as dielectric heating, which rapidly heats up solid phase or semisolid phase food products. The distinct differences between Microwave Wave and Radio Frequency include different regions of the electromagnetic spectrum and frequency ranges. Radio Frequency energy can be generated by passing alternating or direct current thorough food samples located between two electrodes without direct or mechanical contact as shown in figure below, because the electromagnetic field converted from the high electric field is able to stimulate the migration of ions within food products .

Ohmic Heating:

On the contrary to Radio Frequency heating, internal heat dissipation during ohmic heating can be generated by applying an alternating current through food products with direct contact to two electrodes. Ohmic Heating has made considerable contributions to thermal uniformity improvements in single-phase foods. The energy conversion efficiency during OH process is remarkably high as compared with other emerging thermal processing methods. The rate of ohmic heating can be determined by the square of the applied electric field strength and the electrical conductivity of the food.

Importance of Microorganisms in Sterilization and Pasteurization

The main aim behind sterilization and pasteurization process is to inactivate microorganisms and enzymes that cause spoilage and particularly which causes food poisoning. 

Thus the principal reason for characterizing the heat resistance of microorganisms is in order to design a safe sterilization step. 

The goal is to determine the required operating conditions (time/temperature) to achieve sterilization criterion.

One of the major factors that affects a microorganism’s heat resistance is pH. It is possible to classify food products into three groups according to pH:

• Low - acid products: pH ≥ 4.6
• Medium - acid products: 3.7 ≤ pH ≤ 4.6
• Acid products: pH ≤ 3.7

 This is important because the heat resistance of microorganisms is greater at this pH ( ≥ 4.6). On the other hand, fruits,juices and most soups are medium - acid or acid products and require a much softer heat treatment to achieve the sterilization criterion.

1. Vegetative cells 10 min at 80 °C
2. Yeast ascospores 5 min at 60 °C
3. Fungi 30–60 min at 88 °C
4. Bacillus stearothermophilus 4 min at 121.1 °C
5. Clostridium thermosaccharolyticum 3–4min at 121.1 °C
6. Clostridium botulinum spores 3min at 121.1 °C
7. Clostridium botulinum toxins types A and B 0.1–1min at 121.1 °C
8. Clostridium sporogenes 1.5 min at 121.1 °C
9. Bacillus subtilis 0.6 min at 121.1 °C

Need of Non Thermal Processing

Nowadays, most of the liquid foods are processed commercially by Ultra High Temperature (UHT) or High Temperature Short Time (HTST) processes.Though heating liquid foods at high temperature  inactivates enzymes and microorganisms, the organoleptic as well as nutritional properties of the food affect due to denaturation of protein with the loss of vitamins. Hence there is a demand for a non-thermal method processing which is economical, compact, energy efficient, safe, socially and environmentally acceptable and which does not adversely affect nutrition, texture and flavour of the treated food. Consumers are also eagerly claiming high quality, minimally processed foods.

The term ‘non-thermal processing’ is more important for novel non-thermal technologies such as high-pressure processing (HPP), pulsed electric field (PEF), high-intensity ultrasound, ultraviolet light, pulsed light, ionizing radiation and oscillating magnetic fields, intended for microbial inactivation.