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Twin screw extrusion

Identification

Key words Extrusion, TSE, cooking extrusion, high moisture extrusion, structuring, texturized vegetable protein, expansion, cereals, snacks
Latest version 2012/07/17
Completed by DIL

How does it work?

Primary objective Continuous production of products with e.g. meat-like structure or crunchy, aerated structure
Working principle In food processing mostly twin-screw extruders are used to process different kinds of foodstuffs, e.g. breakfast cereals snacks, noodles of meat analogues. Two types are available: co-rotating and counter-rotating twin screw extruders. Main difference is the very high shear rate using a co-rotating twin screw extruder and the build up of a high pressure working with a counter rotating twin screw extruder.
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Figure 1: available types of twin screw extruders (left: co-rotating, right: counter rotating)

High moisture extrusion, the process to produce meat analogues is realized using a co-rotating twin screw extruder (8). Cooking extrusion for expanded snacks and breakfast cereals mainly is realized using a corotating twin screw extruder (1, 2) The mode of working is: At the material charge of the extruder usually a powder mixture is added. In the extruder, the premix is mixed and compressed. Furthermore some water is added using a dosing pump. The mass is homogenized and conveyed by the screws, treated by adjusted special temperature and pressure profile up to 170°C and 90 bar (maximum values for meat analogues). In this way, starch and protein are disrupted and the water is bound. Depending on the application at the end of the extruder, product outlet is realized by a long cooling die for meat analogues or a hole type nozzle to produce e.g. snacks by cooking extrusion. (3, 6, 8, 9) Finally a cutting device at the outlet determines shape and size of the end product.

Images
Additional effects Sterilization by high temperature in extruder, mixing, kneading, moulding

Starch gelatinization Protein denaturation Structure- modification , structure generation

Important process parameters The most important parameters are temperature, pressure, rotation speed, throughput and dwell time, screw profile, screw rotation and die profile.
Important product parameters Product parameters are starch, protein and water content.

Extruder configuration, process parameters and recipe lead to a special shear rate which also influences quality of end product.

What can it be used for?

Products For the cooking extrusion:

The big range of expanded products like breakfast cereals, flat bread and snack products e.g. peanut puffs products. Furthermore many pet food products.

For the high moisture extrusion: Restructured meat or fish products with meat-, poultry or fish like structure based only on vegetable components (8, 10)

Operations Generation of structure and mould, under pressure, high shear rate and high temperature
Solutions for short comings Need for continuous processing in food industry; need for characteristic products with special structure, need for adding value to secondary raw materials

What can it NOT be used for?

Products Special needs to raw materials (for cooking extrusion starch content of 45…70 % (applied to dried matter), for high moisture extrusion protein content <50 %  % (applied to dried matter)) otherwise characteristic structure of end products can not be generated (degree of expansion, stability of shape, …)(1, 2, 3, 7, 8)

Standard treatment for different products, extrusion needs adaption of recipe, process and apparatus configuration. No end product with coarse and lumpy materials; lumpiness of raw materials restricted to a size in the filed of dp < 5...10mm Generating meat-like structures without vegetable proteins.

Operations Production based on extrusion technology requires a lot of experience; a need of trained employee, trouper for running this very sensitive apparatus resp. process
Other limitations High investment cost
Risks or hazards Extrusion, especially cooking extrusion and high moisture extrusion, leads to thermal demands of the material. The high temperature can destroy vitamin, colour and flavours

Implementation

Maturity Available in the pet food industries are the largest and most powerful extruders through rates of up to 16t/h are possible and in the cereals industry are throughput rates up to 12 t / h. Depending on the application, the extruder can be adapted to the various processes.

Also is it possible to work with small extruders in a laboratory scale (throughput to 40 kg/h) e.g. in the pharmacy industry

Modularity /Implementation The continuous mode of working can be easily integrated into existing processes and can undertake tasks of batch processes
Consumer aspects Consumers perceive the technique as environmental friendly and are positive to naturalness of the product.
Legal aspects Extrusion is a long time an established technology in the food industry, no need of special certifications in new applications
Environmental aspects The extruder combines different process types and thus can work more effectively. Concluding other equipment is saved.

Further Information

Institutes DIL, TU Berlin, Gaziantep University, Wageningen UR - FBR
Companies Coperion, KraussMaffei Berstorff, Clextral, Buhler, Leistritz Extrusionstechnik GmbH
References 1) Acioli-Moura, Y.K.C. (2006). Effects of Corn meal, vital wheat gluten, high amylose starch and extrusion parameters on technological properties of wheat-based extruded breading, Journal of Food Quality 29, S. 229-251

2) Arhaliass, A.; Legrand, J.; Vauchel, P.; Fodil-Pacha, F.; Lamer, T.; Bouvier (2009). The effect of wheat and maize flours properties on the expansion mechanism during extrusion cooking, J. Food and Bioprocess Technology 2 (2): 186–193

3) Ding, Q.-B., Ainsworth, P., Plunkett, A., Tucker, G., Marson, H. (2006). The effect of extrusion conditions on the functional and physical properties of wheat-based expanded snacks. Journal of Food Engineering 73 (2): 142-148

4) Fischer, T. (2004). Effect of extrusion cooking on protein modification in wheat flour. European Food Research and Technology 218 (2):128–132

5) Nasehi, B.; Mortazavi, S.A.; Razavi, S.M.A.; Mahallati, M.N.; Karim, R. (2009). Optimization of the extrusion conditions and formulation of spaghetti enriched with full-fat soy flour based on the cooking and color quality. Int. J. of Food Sc. and Nutr. 60 Suppl. (4): 205-214

6) Pfailer, W. (1987). Einfluss der Zusammensetzung von Getreidemahlerzeugnissen und ausgewählter Rezepturen auf das Kochextrusionsverhalten und die Extrudateigenschaften. Dissertation, TU Berlin

7) Akdogan, H.: High moisture food extrusion. International Journal of Food Science and Technology 1999, 34, 195-207

8) Cheftel, J.C.: Continous restructuring of mechanically deboned chicken meat by HTST extrusion cooking. Journal of Food Science 50, 1985

9) Cheftel, J.C. : Influence of process variables on the characteristics of a high moisture fish soy protein mix texturized by extrusion cooking. Lebensmittel, Wissenschaft und Technologie 29, 1996, 526-535

10) Hosaka, H.: Texturization of surimi using a twin-screw extruder. Journal of Japanese Society of Food Science and Technology. 1989, 36, 748-753

Books: Mian N. Riaz: Extruders in Foo, CRC Press, 2000 Mercier, C.; Linko, P.; Harper, J.M.: Extrusion Cooking, 1989 Robin Guy: Extrusion Cooking, Technologies and Applications; CRC Press, 2000+ Medeni Maskan: Advances in Food Extrusion Technology, 2011

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Created by Hamoen on 17 January 2012, at 11:29