Category: Food Engineering

Jul 22

Non Thermal Preservation of Food- High pressure processing (HPP)

High pressure presents unique advantage over conventional food processing including application at low temperature which improves the retention of food quality. High pressure treatment are independent of product size and geometry and their effect is uniform and instantaneous. The food is compressed by uniform pressure from every direction and then returns to original shape when pressure is released.
Processing operation: A sterile container filled with food is sealed and placed in the pressure chamber for pressurizing. Ethylene Vinyl Alcohol (EVOH) and Poly vinyl Alcohol (PVOH) films are recommended for packaging food for high pressure treatment. Also existing multilayer plastic and some aluminum packages may be used. No deformation of the package occurs because the pressure is uniform. The basis of applying high pressure to food is to compress the water surrounding the food. At room temperature, volume of water decreases.  Food is subjected to high pressure for a specified time period. The holding time in the pressure vessel depends on type of food and process temperature. At the end of processing time, the chamber is decompressed to remove treated batch. Read more

Jul 21

Non Thermal Preservation of Food – Dielectric Heating

Dielectric heating is also called microwave heating or high frequency heating. Dielectric energy is form of electromagnetic energy. They are transmitted as wave which penetrate food and are then absorbed and converted into heat.
Principle: the majority of food contain substantial proportion of water. The molecular structure of water consist of negatively charged oxygen atom separated from positively charged hydrogen atom and this form an electric dipole. When a microwave or radio frequency electric field is applied to a food, dipoles in water and in some ionic components such as salt attempt to orient themselves to the field (in a similar way to a compass in a magnetic field). Since the rapidly oscillating electric field changes from positive to negative and back again several million times per second, the dipoles attempt to follow and these rapid reversals create frictional heat. The increase in temperature of water molecules heats surrounding component of food by conduction and or convection. The depth of penetration of microwaves energy is determined by
1. Dielectric constant
2. Loss factor of food Read more

Jul 20

Non Thermal Preservation of Food – Ohmic Heating

Food can be heated by either direct or indirect methods.
Direct heating: In this method of heating, heat is generated within the product. Example; Dielectric heating, Ohmic heating, Pulse Electric Field (PEF), High Pressure Technology (HPT).
Indirect heating: This method of heating relies on heat that is generated externally being applied to the surface of food mostly by radiation, convection and conduction. Example; Infrared heating.
Non thermal preservation of food includes food preservation by following methods.
1. Ohmic heating
2. Dielectric heating
3. Pulse electric field (PEF)
4. High pressure treatment (HPT)
5. Oscillating magnetic field (OMF)
Ohmic heating:
operates by direct passage of electric current through food product with heat generated as a result of electric resistance. In conventional heating, heat travels from heated surface to product by conduction and convection paths. Ohmic heating is also called “resistance heating” or “electro heating”. Here alternating electric current is passed through a food and electrical resistance of the food causes the power to be translated directly into heat. As the food is an electrical component of heater, it is essential that its electrical properties (resistance) are matched to the capacity of heater. Read more

Jul 16

Sieve Analysis

Sieving is a unit operation in which mixture of various sizes of solid particle is separated into two or more fractions by passing over screen. It is applied in industry to determine shape and size of any samples. Sieve analysis has two main objectives.
a. To find out shape of material
b. To find out size of material
In general, there are two types of sieves.
1. Wire woven sieve
2. Perforated sieve

 

 

 

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Jul 15

Theory of Size Reduction

Size reduction is the process of breaking down solid particle to smaller one. When energy is applied in the form of a stress on a material, it breaks into two or more pieces resulting in generation of new surface area. Energy is used to break or overcome the intramolecular forces of the solid particles so that they are broken into pieces and new area is created. Size reduction is also known as comminution in engineering literature. Size reduction is commonly used in food industries with many purposes. some of the purposes are given below. Read more

Jul 11

Size Reduction Equipment

There are various size reduction equipment and have different principle. The common working principles in food industries are slicing (as in preparing potato chips), dicing (cutting into cubes), shredding (shear force as in wheat milling), grinding (impact force as in making spice powder), crushing and pulping (as in fruit juice extraction). However, size reduction equipment are not only used in food processing industries. It is also widely used in construction industries. Common examples are; Jaw crusher and Gyratory crusher.

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