Eight modern technics to protect food products were introduced in previous post. Other types of industrial food dryers we will introduce are Microwave technic, Infrared technic, Electric heating, High pressure, Electric pulse, Irradiation and Ultrasonic.
Microwave technic to protect food products
The microwave method uses microwaves with a frequency of 3 to 30 GHz and the heat energy generated. This method is mostly used for drying potato chips, peas, onions, beans, and vegetables by rotating hot air or vacuum. Water activity and moisture reduction increase the products’ shelf life. The application of this method includes
- Acceleration of baking (cakes, bread, and pastries) and reduction of fat absorption
- Acceleration of drying (cereals, pastries, onions, and potato chips)
- Acceleration of defrosting
The advantages of microwave heating method to increase the shelf life of food include high heating rate, time saving and volumetric heating instead of surface heating.
Infrared technic
Infrared rays are visible microwaves that are divided into 3 categories: long waves (30 micrometers), medium waves (3 micrometers), and short waves (1 micrometer). The waves in this drying method have a penetration depth of several mm and have a similar effect to microwaves and high-frequency waves and are suitable for low-thickness foods.
This method is used for drying low moisture foods such as slices of bread, beans, and tea, drying fish and vegetables, pasta and rice, flour and frying meat in the preheating stage, roasting coffee, baking pizza, and bread, biscuits, and defrosting food. The infrared method is much more effective in bakery products than other methods. The advantages of this technic are high and effective heat transfer, reduction of cooking time, small and flexible ovens, quick adjustment and control, and relatively cheap price.
Electric heating method (electromagnetic waves)
The direct energy transfer from the electromagnetic source to the food is used in this technic. The purpose of this method is to convert electrical energy into thermal energy and use this heat to kill microorganisms. This heat is generated by an element that is a simple electrical resistor. Energy consumption in this method is high, but its thermal efficiency is higher than the microwave method and there is no limit to the depth of penetration. The advantages of this technic include:
- Ease of process control
- Reduction of maintenance costs
- Reduction of the risk of sediment at the level of heat transfer and burning of food products
- Better preservation of nutrients and vitamins
- Being safe and secure for the environment
- Higher uniformity in heating the food compared to the microwave method
The applications of electric heating technic and using the electric resistance include:
- In aseptic processing of ready-to-eat foods for storage and distribution at room temperature
- Pasteurizing food products containing solid particles for hot filling
- Preliminary heating of products before sterilization in cans
- Healthy production of ready-to-eat foods for storage and distribution at refrigerated temperatures
High pressure technic
3000-8000 bar pressure is used in this technic. This was first used in the 1990s to pasteurize acidic foods. This method is used to increase the shelf life of fruits, citrus juices, jams, sauces, yogurt, and meat. The vegetative cells are inactivated at a pressure of 3000 bar in this technic by increasing the pressure and changing the cell structure and permeability of the cell membrane. In addition, spores die at the pressure of 6000 bar and a temperature of 60-70 °C. Enzymes are inactivated at 3000 bar. It is a non-thermal process in which spores, enzymes, and microorganisms of solid or liquid food are inactivated at low temperatures under high pressure. Thus, the food shelf life increases. High-pressure technology is used to increase food shelf life, defrost and preserve food.
This method is used in fruits and juices, meat products, dairy products, cereals, and vegetables.
This method cannot be used for foods containing foam and materials sensitive to dielectric decomposition.
One of the advantages of this method is less energy consumption.
Ultrasonic technic
The structure of microorganisms and pathogens is damaged by producing ultrasound products in ultrasound technic that are not audible to humans (above 20KHz). These waves are not visible but cause dizziness and nausea. This technic is mostly used for exports. This is simple and inexpensive and is economical in terms of energy consumption. Ultrasonic technology is used in disinfecting and removing the microbial load of dried fruits, dried vegetables, dairy products, meat and fish, fresh fruits and vegetables, cereals, aqueous solutions and gels, emulsion, and fat products, honey, etc.
Pasteurization and sterilization, two common thermal methods, are used to inactivate microorganisms in food products, but high temperatures destroy the nutritional value of food products and products. However, ultrasound waves have a low temperature and, like other anti-microbial methods, low temperature can maintain the taste and nutritional value of food while inactivating microorganisms.
The antibacterial power of ultrasound depends on the frequency, amplitude, and volume of the present bacteria. The advantages of the ultrasound technic are no need to use and store hazardous chemicals and not cause mutations and cancer.
Electric pulse technic
Electric pulse technic is actually the creation of pulsed electric fields and non-thermal storage technology. This method does not leave an undesirable change on the food because it uses high voltage pulsed electric fields in a short time for food placed between the two electrodes. This high voltage creates an electric field and thus affects the microorganisms. This technic can better preserve the organoleptic properties of food, nutrients, vitamins, texture, and flavor, as well as the microstructure of the food due to its non-thermal effect and short operating time compared to samples to which the thermal process is applied. Therefore, the quality characteristics of food are preserved and this method is preferable to thermal methods.
This method is used for pasteurization of milk, pasteurization of eggs, processing of fruit extracts, processing of potatoes, etc.
Irradiation technic to protect food products
As mentioned in detail about radiation, radiation is one of the non-thermal methods to fight germs and increase shelf life. The popular technics in irradiation are gamma-ray (using cobalt 60 and cesium-137), electron beams (linear accelerators), and X-rays. Therefore, physical and non-thermal methods are used to kill microorganisms, prevent germination, sterilize dried fruits, dried vegetables, and spices, control microorganisms and increase the shelf life of products.