Food industry extrusion processes

In 2002, the world production of polymers (not including synthetic libers and rubbers) was ca. 190 million metric tons. Of these, the combined production of poly(ethylene terephthalate), low- and high-density polyethyelene, polypropylene, poly(vinyl chloride), polystyrene, and polyurethane was 152.3 milhon metric tons [1]. These synthetic, petroleum-based polymers are used, inter alia, as engineering plastics, for packing, in the construction-, car-, truck- and food-industry. They are chemically very stable, and can be processed by injection molding, and by extrusion from the melt in a variety of forms. These attractive features, however, are associated with two main problems ... 

Extrusion is the first really new technology to arrive in the food industry for many years. Tunnel ovens are a development of an oven while the sort of mixer used for the CBP process is a development of a mixer, albeit one that can apply a great deal of energy in a short time. 

The production of foamed films and sheets from polypropylene and polystyrene is discussed, with particular reference to packaging applications. Advantages of foamed materials for this application are examined, and the chemical and physical foaming processes are described. Extrusion technology for film and sheet by chemical and physical foaming processes is discussed, and recent developments in the coextrusion of multilayer packaging trays for the food industry are considered. 

Tab. 6.4-6 Listing of some materials that are processed with roller extrusion presses and associated equipment in the food industry (in alphabetical order)...

Tab. 6.4-5 List of some dry and dried food materials as well as mixed food formulations that are converted by growth agglomeration into free flowing, granulated, often instant, and dust free products for easy packaging, metering, and reconstitution Tab. 6.4-6 Listing of some materials that are processed wifli roller extrusion presses and associated equipment in the food industry (in alphabetical order)...

The extrusion process is very well established in the plastic and food industry. This technology for the manufacturing of the enzymes-containing granulate combines the advantage of a homogeneous particle size distribution with low-cost ingredients. 

In many chemical and processing applications, fluids need to be heated or cooled and a wide range of equipment may be utilized. Examples include double pipe and shell and tube heat exchangers, and stirred vessels fitted with cooling coils or jackets. Sometimes, heat is generated in the process, as in extrusion which is extensively carried out in the polymer and food industry. It may also be necessary to reduce the rate at which heat is lost from a vessel or to ensure that heat is removed at a sufficient rate in equipment such as screw conveyors. In most applications, it is the rate of heat transfer within process equipment which is of principal interest. However, with thermally sensitive materials (such as foodstuffs, fermentation froths, pharmaceutical formulations), the temperature profiles must be known and maximum permissible temperatures must not be exceeded. 

Despite the fact that TPS is considered a new material in technological terms, its basic features and processes are in fact the same as those relative to extrusion-cooking starch used in the food industry since the 1960s. This kind of processing is therefore briefly described briefly in the heading, given its importance in the development of TPS. 

Many different materials are formed through an extrusion process metals, clays, ceramics, foodstuffs, etc. The food industry, in particular, makes frequent use of extruders to make noodles, sausages, snacks, cereal, and numerous other items. In this book, the materials that will be treated are confined to polymers or plastics. 

Native ceUulose is added to some foods as a non-calorific thickener, causing turbidity and is added to products processed by extrusion. However, modified celluloses have more appUcations in the food industry. CeUulose can be modified by either physical or chemical processes. 

If reactants A and B, and product C, are fluids, then continuous flow, solvent-free conditions may be suitable. This does, however, pose practical problems of efficient mixing between A and B, which can be made more difficult if either is viscous, or the reactions are fast. Within the polymer and food industries there are examples of both continuous solid and melt extrusion processes, though few involve reactive chemistiy. If the reaction is selective then product C can be isolated directly, otherwise its higher molecular weight may make it difficult to separate without using a solvent, negating the aim, unless it is a solid. An example of a solvent-free continuous flow process is the lipase-catalyzed esterification of fatly esters using alcohols, as shown in Scheme 12.1. ... 

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