Extrusion-Cooking Techniques

Applications, Theory and Sustainability

Leszek Moscicki

• Publisher: Wiley-VCH
• Year: 2011
• Print ISBN:
  9783527328888
• Edition: 1
• eBook ISBN:
  9783527634101
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Offering an engineering perspective and the latest information on the application of this rapidly expanding technique, this practical book covers the technology, engineering, materials and products, as well as economic and ecological aspects. In addition to the theory, it also utilizes case studies that can easily be put into industrial practice.
Each step of the process is discussed in terms of sustainability, and all data complies with the EU and FTA environmental regulations.
Invaluable reading for food chemists and technologists, process engineers, chemists in industry, agricultural scientists, and chemical engineers.

From the Contents:

* Engineering Aspects of Extrusion
* Raw Materials in the Production of Extrudates
* Production of Breakfast Cereals, Snack Pellets, Baby Food and more
* Extrusion Technique in Confectionery
* Pet Food and Aquafeed
* Extrusion-Cooking in Waste Management and Paper Pulp Processing
* Thermoplastic Starch
* Expanders
* Process Automation
* Scale-Up of Extrusion-Cooking in Single-Screw Extruders

Chapter 1

Extrusion-Cooking and Related Technique

Leszek Mo

cicki and Dick J. van Zuilichem

1.1 Extrusion-Cooking Technology

Extrusion technology, well-known in the plastics industry, has now become a widely used technology in the agri-food processing industry, where it is referred to as extrusion-cooking. It has been employed for the production of so-called engineered food and special feed.

Generally speaking, extrusion-cooking of vegetable raw materials deals with extrusion of ground material at baro-thermal conditions. With the help of shear energy, exerted by the rotating screw, and additional heating of the barrel, the food material is heated to its melting point or plasticating point [1, 2]. In this changed rheological status the food is conveyed under high pressure through a die or a series of dies and the product expands to its final shape. This results in very different physical and chemical properties of the extrudates compared to those of the raw materials used.

Food extruders (extrusion-cookers) belong to the family of HTST (high temperature short time)-equipment, capable of performing cooking tasks under high pressure. This is advantageous for vulnerable food and feed as exposure to high temperatures for only a short time will restrict unwanted denaturation effects on, for example, proteins, amino acids, vitamins, starches and enzymes. Physical technological aspects like heat transfer, mass transfer, momentum transfer, residence time and residence time distribution have a strong impact on the food and feed properties during extrusion-cooking and can drastically influence the final product quality. An extrusion-cooker is a process reactor [2], in which the designer has created the prerequisites with the presence of a certain screw lay-out, the use of mixing elements, the clearances in the gaps, the installed motor power and barrel heating and cooking capacity, to control a food and feed reaction. Proper use of these factors allow to stimulate transformation of processed materials due to heating, for example, the denaturation of proteins in the presence of water and the rupture of starches, both affected by the combined effects of heat and shear. These reactions can also be provoked by the presence of a distinct biochemical or chemical component like an enzyme or a pH controlling agent. When we consider the cooking extruder to be more than just a simple plasticating unit, a thorough investigation of the different physical technological aspects is more than desirable.

Currently, extrusion-cooking as a method is used for the manufacture of many foodstuffs, ranging from the simplest expanded snacks to highly-processed meat analogues (see Figure 1.1). The most popular extrusion-cooked products include:

• direct extruded snacks, RTE (ready-to-eat) cereal flakes and a variety of breakfast foods produced from cereal material and differing in shape, color and taste and easy to handle in terms of production;
• snack pellets – half products destined for fried or hot air expanded snacks, pre-cooked pasta;
• baby food, pre-cooked flours, instant concentrates, functional components;
• pet food, aquafeed, feed concentrates and calf-milk replacers;
• texturized vegetable protein (mainly from soybeans, though not always) used in the production of meat analogues;
• crispbread, bread crumbs, emulsions and pastes;
• baro-thermally processed products for the pharmaceutical, chemical, paper and brewing industry;
• confectionery: different kinds of sweets, chewing gum.

The growing popularity of extrusion-cooking in the global agri-food industry, caused mainly by its practical character, led many indigenous manufacturers to implement it on an industrial scale, based on the local raw materials and supported by detailed economic studies based on the domestic conditions [18]. Extrusion-cooking offers a chance to use raw materials which have not previously displayed great economic importance (e.g., faba bean) or have even been regarded as waste. The domestic market has been enriched with a category of high-quality products belonging to the convenience and/or functional food sector. Of practical importance is the fact that the process in question can be implemented with relatively low effort, does not require excessive capital investment, and most equipment is user-friendly and offers multiple applications.

For easier understanding of the extrusion-cooking technology, as an example, we would like to present the most simple production – direct extrusion of cereal snacks with different shapes and flavors. We will give a general overview of the technological process using a standard set of processing equipment commonly used in such a case.

1.1.1 Preparation of Raw Material

The manner of preparation of the raw material to be processed into food preparations depends upon the ingredients used. In the case of direct extruded snacks this is mainly cereal-based material. Depending on its quality, it must be properly ground and weighed according to the recipe and mixed thoroughly before being fed to the extruder. When conditioning is required, before mixing, water in some quantity is necessarily added for the preparation of the material.

Figure 1.1 Assortment of popular extrudates.

Figure 1.2 presents a diagram of a standard installation for the production of direct extrusion and multi-flavor snacks. In the case of simple maize snacks, that is, not enriched and being single-component products, the processing line is significantly simplified. If is often enough to operate an extruder, for example the one presented in Figure 1.3, and a packing machine to initiate production (often called “garage box production”).

Figure 1.2 A diagram of the set-up for the production of multi-flavor cereal snacks [1]: 1 – a silo with raw materials, 2 – pneumatic conveyer, 3 – collector, 4 – mixer, 5 – weigher, 6 – conditioner, 7 – extruder, 8 – cutter, 9 – dryer, 10 – screen, 11 – recycling of dust, 12 – coating drums, 13 – silos of finished product, 14 – packing machine.

Figure 1.3 Single-screw extrusion-cooker, type TS-45 (designed by L. Moscicki), equipped with an electric heating system and a water-air cooling system [1].

1.1.2 Extrusion-Cooking

The effect of direct extrusion-cooking is that, after leaving the die, the material expands rapidly and the extrudates are structurally similar to a honeycomb, shaped by the bundles of molten protein fibers. In this case a simple, single-screw food extruder can be used to manufacture various types of products, different in shape, color, taste and texture [1, 3–5]. The technology for each of them requires an appropriate distribution of temperature, pressure and moisture content of the material during processing. Because the main task is to obtain good-quality extrudates, flexibility and precise control, especially of the thermal process, is essential in the design and construction of modern cooking extruders. More than often, the process for the manufacture of specific products has to be developed empirically.

Particularly interesting are the issues related to the energy consumption of extrusion-cooking of vegetable raw materials. There is a widespread opinion that this power consumption is too high. It is not clear to us on what these opinions are based, since the results of our own research and of those available from the literature mention something completely opposite. Measurements of energy consumption in single-screw food extruders are in the range 0.1–0.2 k Wh kg⁻¹ (excluding of course, the costs of material preparation, that is, the grinding and conditioning) [1]. This demonstrates that extrusion-cooking is highly competitive in comparison with the conventional methods of thermal processing of vegetable material. Of course, this does not mean that extrusion-cooking is ideal for all applications. It is an alternative and, in many cases, competitive in relation to other methods of food and feed manufacture.

1.1.3 Forming, Drying and Packing

Depending on the purpose for which they are to be used, extrudates must be suitably formed. The melt mass leaving the extruder takes more or less the shape of the extruder-dies(nozzle); at the same time a lengthwise arrang...

Table of contents

• Cover
• Further Reading
• Title Page
• Copyright
• Preface
• List of Contributors
• Chapter 1: Extrusion-Cooking and Related Technique
• Chapter 2: Engineering Aspects of Extrusion
• Chapter 3: Raw Materials in the Production of Extrudates
• Chapter 4: Production of Breakfast Cereals
• Chapter 5: Snack Pellets
• Chapter 6: Crispbread, Bread Crumbs and Baby Food
• Chapter 7: Precooked Pasta
• Chapter 8: Processing of Full Fat Soybeans and Textured Vegetable Proteins
• Chapter 9: Extrusion Technique in Confectionery
• Chapter 10: Pet Food and Aquafeed
• Chapter 11: Expanders
• Chapter 12: Extrusion-Cooking in Waste Management and Paper Pulp Processing
• Chapter 13: Process Automation
• Chapter 14: Thermoplastic Starch
• Chapter 15: Scale-Up of Extrusion-Cooking in Single-Screw Extruders
• Chapter 16: Producers of Food Extruders and Expanders
• Index