Ultrasound Processing Technology in Food Industry

Most people are familiar with the use of ultrasound by bats and dolphins for navigation and detection of food. Earlier ultrasound was used to be commonly associated with biomedical field, but today it founds numerous applications in food processing industries  for  development of safe and cost effective quality products for consumers. This revolutionary technology has received a good deal of interest due to its green nature and nonthermal benefits, which include increased throughput, reduced cost, improved final product quality, process simplification, and reduced energy usage.

The ultrasound technology is being carried out in various areas of food processing technology namely crystallization, freezing, bleaching, degassing, extraction, drying, filtration, emulsification, sterilization, cutting, etc. It is being applied as an effective preservation tool in many food-processing fields viz. vegetables and fruits, cereal products, honey, gels, proteins, enzymes, microbial inactivation, cereal technology, water treatment, diary technology, etc.

Ultrasound- Definition

Ultrasound are mechanical sound waves that originate from molecular movements that oscillate in a propagation medium. These waves have frequency beyond the hearing capacity of human ears i.e.  above 20 kHz. When the ultrasound propagates through a material it induces compressions and decompressions (rarefactions) in the particles of the medium, due to which high amount of energy is produced. The basic principle behind working of ultrasound is that it utilizes interaction between high-frequency sound waves and matter to obtain information about the composition, structure and dimensions of materials through which it propagates. These waves are longitudinal as the oscillatory movement of the particles in transmission medium is parallel to the propagation direction. Thus it can transverse in all types of media i.e. solid , liquid and gas. Ultrasound has various effects on different systems. On solids it effects through vibrational energy for cutting and melting, in liquids it effects by the production of intense cavitation and in gases it affects by producing high-intensity acoustic fields.

Ultrasound Waves Classification

In food industries, normally two categories of ultrasounds are used which are classified  on the basis of operating frequencies. These are as follows:

  1. Non-Destructive Type:

These are low energy – high frequency diagnostic sound  waves that have frequency above 1MHz-10Mhz and have intensities down 1 Wcm 2. These can be used as monitoring of physiochemical properties and composition food products while processing and storage. It also evaluates composition of meat products, poultry and fish of raw and fermented stages. These are also used for the quality control of fresh vegetables and fruits in both pre- and postharvest, cheese during processing, commercial cooking oils, bread and cereal products, bulk and emulsified fat based food products, food gels, aerated and frozen foods.

  1. Processing Type:

These are high energy low frequency  type sound waves  that have frequencies between 20KHz-1 MHz and have intensity above 1 Wcm2. These are disruptive in nature and have effect on mechanical, physical, or biochemical properties of foods through cavitation. This is used for controlling microstructures and modification, emulsification, befoaming of food products. It also has role in freezing, thawing, microbial inactivation, drying etc.

Ultrasound Generator System

It is electricity driven ultrasonic system, which has basically three parts:

  1. Power Generator

It provides energy for the system, which in most cases is an electrical current. 

  1. Transducer

It is the central element of ultrasound generator system that converts electrical energy (or mechanical energy) into sound energy through mechanical vibrations at ultrasonic frequencies. Most common commercial transducers that are used in food industries are piezoelectric, but some are magneto-strictive also. Piezoelectric transducers convert cyclic electrical current into physical vibrations, and magneto-strictive devices convert varying magnetic fields into physical vibrations.

  1. Emitter

It is used for radiating / amplifying ultrasonic waves from the transducer into the medium. Emitters can come in the form of baths, horns, or sonotrodes. The shape and size of the emitter controls the amount of amplification. Common shapes for emitters include knives, nozzles, or dies.

Forms of Ultrasound Technology

  1. Ultra-sonication: It is the application of ultrasound at low temperature and require high energy. It is mainly used for heat sensible products. This method requires long treatment time to inactivate stable enzymes.
  2. Mano-sonication: It is combined method in which ultrasound and pressure are applied together. Moderate pressures at low temperatures are combined in this. Upon combination inactivation efficiency is higher than ultrasound alone.
  3. Thermo-sonication: This method is the combination of ultrasound and heat. It produces a greater effect on inactivation of microorganisms than heat alone and is commonly employed for liquid food preservation.
  4. Manothermo-sonication: It is combined method of heat, ultrasound and pressure. This method inactivates several enzymes at lower temperatures in a shorter time than thermal treatments. Microorganisms that have high thermotolerance can be inactivated by manothermosonication

Equipments using Ultrasound Technology

  1. Cheese Cutting Machine
  2. Sandwich Cutting Machine
  3. Ultrasonic Sealing Machine for blister packs and stand up pouches
  4. Ultrasonic Homogenizer
  5. Ultrasound Wad Sealing Machine

Ultrasound is a nonthermal processing technique that offers broad range of applications such as mass transfer, food preservation, assistance in thermal treatments and manipulation of texture and food analysis. This technology can increase process efficiency through enhanced yields, increased throughput and reduced processing costs as well as modify biomaterial structure.

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