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Extrusion Technology in Food Processing

Food extrusion is a form of extrusion used in food processing. It is a process by which a set of mixed ingredients are forced through an opening in a perforated plate or die with a design specific to the food, and is then cut to a specified size by blades.

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Extrusion Technology in Food Processing

  1. 1. FOOD PROCESSING Extrusion Technology In of Food Processing Er. Shelke G.N Assistant Professor Department of Food Engineering CFT Ashti, Maharashtra 414202 Phone: +919561777282 E-mail: shelkeganesh838@gmail.com
  2. 2. Point to be covered  Introduction.  Advantages of Extrusion  Advantages of Extrusion  Popularity of Extrusion Cooking  Principle of Extrusion Cooking  Classification of Extruders  Factors Affecting Extrusion Cooking
  3. 3. Extrusion cooking is a modern (HTST) cooking process (thermo-mechanical process) in which heat transfer, mass transfer, pressure changes and shear are combined to produce effects such as,  Cooking,  Sterilization,  Drying,  Melting,  Cooling,  Texturizing,  Conveying,  Puffing,  Mixing,  Kneading,  Forming, etc. It is important food process in the manufacture of pasta, ready‐to‐eat cereals, snacks, pet foods Introduction
  4. 4.  Extrusion-technology is gaining increasing popularity in the global agro-food processing  Extrusion cooking technologies are used for cereal and protein processing in food.  Now a day’s consumers do choice for nutritionally rich, therapeutic benefits and for attractiveness especially in case of baby foods.  Thus to obtain above mentioned designer food, Food Extrusion technology is used. Introduction
  5. 5.  Extrusion cooking is a high-temperature short-time (HTST) process.  which reduces microbial contamination and inactivates enzymes.  The main method of preservation of both hot- and cold-extruded foods is by the low water activity of the product (0.1–0.4), and for semi-moist products in particular, by the packaging materials that are used. Introduction
  6. 6.  Extrusion brings gelatinization of starch, denaturation of proteins,  Modification of lipids inactivation of enzymes and many anti nutritional factors,  It reduces microbial contamination, and inactivates enzymes. Introduction
  7. 7. Advantages of extrusion  Adaptability: The extrusion process is remarkably adaptable in being able to accommodate the demand by consumers for new product
  8. 8.  Product characteristics: A variety of shapes, texture, color and appearances can be produced, which is not easily formed using other production methods
  9. 9.  Energy efficient: Extruders operate at relatively low moisture while cooking food products, so less re-drying is required
  10. 10.  Low cost: extrusion has lower processing costs than other cooking and forming processes. We can save 19 per cent raw material, 14 per cent labor and 44 per cent capital investment
  11. 11.  Less space: extrusion processing needs less space per unit of operation than other cooking system
  12. 12. Popularity of Extrusion Cooking  Versatility: A wide range of products, many of which cannot be produced easily by any other process, is possible by changing the ingredients, extruder operating conditions and dies.  Cost: Extrusion has lower processing costs and higher productivity than other cooking and forming processes  Productivity: Extruders can operate continuously with high out put
  13. 13. Popularity of Extrusion Cooking…… Product quality: Extrusion cooking involves high temperatures applied for a short time, retaining many heat sensitive components of a food Environmentally-friendly: As a low-moisture process, extrusion cooking does not produce significant process effluents, reducing water treatment costs and levels of environmental pollution
  14. 14. History Of The Extruder
  15. 15. Principle of Extrusion Cooking  The raw materials are allowed into the extruder barrel and the screw(s) then convey the food along it.  Further down the barrel, smaller flights restrict the volume and increase the resistance to movement of the food.
  16. 16. Principle of Extrusion Cooking ……  As a result, it fills the barrel and the spaces between the screw flights and becomes compressed.  As it moves further along the barrel, the screw kneads the material into a semi-solid, plasticized mass.  If the food is heated above 100ºC the process is known as extrusion cooking (or hot extrusion).
  17. 17. Principle of Extrusion Cooking …  Here, frictional heat and any additional heating that is used cause the temperature to rise rapidly.  High temperature of operation in presence of water promotes gelatinization of starch components and stretching of expandable components.
  18. 18. Principle of Extrusion Cooking ……  The food is then passed to the section of the barrel having the smallest flights, where pressure and shearing is further increased.  Finally, it is forced through one or more restricted openings (dies) at the discharge end of the barrel as the food emerges under pressure from the die, it expands to the final shape and cools rapidly as moisture is flashed off as steam.
  19. 19. Examples for Extrusion Foods  Pasta Ready-to-eat (RTE) cereals Puffed cereals, shredded cereals, etc.  Snack products Corn curls, puffed snacks, crisp breads, co extruded products, etc.  Pet foods Dry, semi moist  Confectionery products Licorice, toffee, caramel, peanut brittle  Texturized proteins Meat analogs, fish paste (surimi)
  20. 20. The basic elements of proper extrusion cooking are the following: 1) Feeding of granular or milled material in the extruder should be continuous at desired feed rates. 2) The material should be pre-conditioned with steam at controlled temperature of 800 C to 800C at atmospheric pressure. 3) The moisture should be uniformly applied to the product. 4) The equipment must transform the granular or processed floury material into a dough at 820 C to 1100 C
  21. 21. 5) The temperature of the dough should be elevated to 1150 C to 2000 C during last 10 to 30 seconds in their extruder to cook and expand the product. 6) Formation of desired shape and size of the product by a nozzle or die at the end of the process the extrudate is cut into desired lengths. 7) Drying and cooling of the extrudate.
  22. 22. Classification of Extruders
  23. 23.  Hot Extrusion: If the food is heated above 100ºC the process is known as extrusion cooking.  Cold Extruders: If the food is heated below 100ºC the process is known as cold extrusion.  The main method of preservation of both hot- and cold-extruded foods is by the low water activity of the product (0.1–0.4)
  24. 24. Cold extrusion  In this process, the product is extruded without cooking or distortion of the food.  The extruder has a deep-flighted screw, which operates at a low speed in a smooth barrel, to knead and extrude the material with little friction.  It is used to produce pasta, hot dogs, pastry Dough and some types of confectionery.  Typical operating conditions are shown in Table 14.2 for low shear conditions.
  25. 25. Hot Extrusion cooking  High pressures and temperatures are used to form expanded products.  The rapid release of pressure as the food emerges from the die causes instantaneous expansion of steam and gas in the material, to form a low-density product.  Hot extrusion is a HTST process, which minimizes the loss of nutrients and reduces microbial contamination.  The moisture content of some products, for example snack foods, crispbread and breakfast cereals, is further reduced after extrusion by drying.
  26. 26. Single-screw extruders  These contain a single rotating screw in a metal barrel, and come in varying patterns.  The most commonly used single-screws have a constant pitch.  Single-screws usually consist of three sections. 1) Feed 2) Transition or compression 3) Metering
  27. 27. Feed section  The portion of the screw which accepts the food materials at the feed port.  Usually the feed section is characterized by deep flights so that the product can easily fall in to the flights.  The function of the feed section is to assure sufficient material moved or conveyed down the screw and the screw is completely filled.
  28. 28. Compression section  The portion of the screw between the feed section and the metering section is called as compression section.  The food ingredients are normally heated and worked into a continuous dough mass during passage through the transition section.  The shearing/compression section in which the materials are thoroughly worked into viscous dough, partially cooked and elevated in temperature and pressure;
  29. 29. Metering section  The portion of the section nearest the discharge of the extruder which is normally characterized by having very shallow flights.  The shallow flights increase the shear rate in the channel to the maximum level with in the screw.  The metering section in which dough is further cooked and starch granules may be broken down due to higher shear forces.  The metering section continuously feeds the die with materials at uniform pressure;
  30. 30.  The raw materials are fed in a granular form at the hopper located in the feed section.  The rotating action of the screw conveys the material to the transition section.  In the transition section, the screw channel becomes shallower and the material is compacted.  A major portion of mechanical energy is dissipated in this section, which results in a rise in temperature of the material.  Starch becomes gelatinized, and the material becomes more cohesive.
  31. 31.  It is transported further by the metering section and pushed through the die opening.  The barrels of single-screw extruders usually have helical or axial grooves on the inner surfaces.  This helps to convey and mix the material more effectively.  Single-screw extruders are usually characterized by their length to diameter (L/D) ratio and their compression ratio.  The throughput (mass flow rate) capacity of a single-screw extruder is linked to screw speed, screw geometries, and material characteristics.
  32. 32. Extruder Parts & Components Extrusion Drive:  The Power supply in food extruder is done by Electric motors.  The size of the motor depends on the capacity of the extruder and may be as large as 300 KW.  The screw speed on extruder is a valuable control parameter.  The speed on food extruders is normally less than 500 rpm.  Thrust bearing must be able to sustain the load produced under normal extrusion conditions giving an expected life of 20,000 to 50,000 hr.
  33. 33. Feeder:  A device providing a uniform delivery of food ingredients which are often sticky, non-free- flowing substances.  It will regulate rate/pressure of flow. Some types of feeders commonly used are vibratory feeders, variable speed auger and weigh belts.
  34. 34. Barrel or sleeves  The barrel is divided into feeding, kneading an the sleeves surrounding the screw can be solid.  They are often jacketed to permit circulating of steam or superheated oil for heating and water or air for cooling.
  35. 35. Screw  The screw of the extruder is certainly its most important component  The screw which conveys the materials.  Diameter of the screw of a single screw extruder normally varies between 2-15 cm.  Length to diameter ratio varies between 8- 20 and helix angle between 20o – 30o .
  36. 36. Die or nozzle:  The die presents two main functions: give shape to the final product and promote resistance.  It increase in internal pressure.  The die can present various designs and number of orifices .  Dies may be designed to be highly restrictive, giving increased barrel fill, residence time and energy input.  Die design and its effects on functional properties and quality of a final product.
  37. 37. Cutting mechanism  The cutting mechanism must permit obtaining final products with uniform size.  Product size is determined by the rotation speed of the cutting blades.  This mechanism can be horizontal or vertical Advantages of Single-screw extruders 1) It is a short time process 2) No waste products 3) Versatility in application
  38. 38. Twin-screw extruders  The term ‘twin-screw’ applies to extruder s with two screws of equal length placed inside the same barrel.  It consists of two parallel screws in a barrel.  It is more complicated than single screw extruders.  It provides much more flexibility and better control.  Twin screws produce a more uniform flow of the product through the barrel due to the positive pumping action of the screw flights.
  39. 39. Twin-screw extruders are mainly of two types as follows. Counter- rotating twin- screw extruder 1) Non-intermeshed, counter rotating 2) Intermeshed, counter rotating Co-rotating twin-screw extruders 1) Non-intermeshed, co-rotating 2) Intermeshed, co-rotating
  40. 40. Advantages of Twin Screw Extruders 1) Handle viscous, oily, sticky or very wet material and some other products which will slip in single screw extruder, (it is possible to add up to 25% fat in a twin screw extruder) 2) Less wear in smaller part of the machine than in single screw extruder. 3) Wide range of particle size (from fine powder to grains) may be used, whereas single screw is limited to a specific range of particle size
  41. 41. Characteristics of Extruded Products  Degree of Expansion on Exit from the Extruder.  For many products, the sudden release of pressure when exiting the die of the extruder causes water to flash off and the product to expand.  The extent of expansion depends on the composition of the product, its internal microstructure as it exits the die, and the conditions (pressure and temperature) in the extruder.  Degree of expansion may be calculated as either the ratio of the diameters or areas of the extruded product to the die
  42. 42.  Bulk Density. The density of the final product depends on the nature of the solid material as well as on the amount of air space within the product. A highly expanded product, with plenty of air spaces, has significantly lower bulk density than a product with little air inclusion.
  43. 43.  Mechanical Properties.  Physical and rheological properties determine the characteristics of the extruded product.  These may be expressed as fundamental parameters, like elastic modulus, or may be characterized by Empirical measures, such as hardness or crispness.  Instruments that measure fundamental properties (rheometers) or empirical techniques (Instron or penetrometer) may be used to quantify characteristics of extruded products.
  44. 44.  Internal Microstructure.  The arrangement of the components of the extruded product leads to the physical properties described above.  The state of starch, whether partially or completely gelatinized, in the final product strongly influences physical characteristics.  Typically, internal microstructure is evaluated using microscopy (scanning electron microscopy).
  45. 45.  Protein Quality.  The nature of extruded proteins depends on the Extruder operating conditions, especially temperature profile as the extruded product is formed.  High-heat treatment causes denaturation of many proteins, which influences physical characteristics such as viscosity.
  46. 46.  Starch Characteristics.  Properties of starch in an extruded product that influence quality characteristics include such measures as water absorption index, water solubility index, and enzyme susceptibility.  These depend on the operating parameters within the extruder as well as the type of raw materials used for extrusion.
  47. 47. Factors Affecting Extrusion Cooking Rheological properties of the food The properties of the feed material have an important influence on the texture and color of the product; the most important factors are: 1) The type of feed materials 2) Their moisture content 3) The physical state of the materials 4) Their chemical composition, particularly the amounts and types of starches, proteins, fats and sugars 5) The pH of the moistened material. 6) Feed rate 7) Screw speed 8) Barrel temperature 9) Die characteristics 10) Screw design
  48. 48. Operating characteristics The most important operating parameters in an extruder are 1) Temperature Increase in extrusion temperature results in higher degree of gelatinization. 2) Pressure 3) Diameter of the die apertures Increase in diameter reduces gelatinization of starch 4) Shear rate 5) Moisture If moisture increases viscosity decrease torque decrease product temperature decrease bulk density increase (expansions die pressure decreases).

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Food extrusion is a form of extrusion used in food processing. It is a process by which a set of mixed ingredients are forced through an opening in a perforated plate or die with a design specific to the food, and is then cut to a specified size by blades.


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