If developing economies are to eradicate poverty and achieve food and nutrition security, more effort is needed in harnessing extrusion technology for producing safe food utilizing locally grown legumes and cereal grains.
Extrusion technology is central to value addition to agricultural commodities, especially cereals/legumes, to enhance food security and sustainable development. It is a powerful processing operation, which can produce products with unique textural properties having high and low density, as well as highly expanded and condensed products, depending on the processing condition. Extrusion is a process that combines several unit operations, including mixing, cooking, kneading, shearing, shaping, and forming (Riaz, 2013a).
The high-temperature short-time (HTST) process usually reduces microbial contamination, inactivates enzymes, and facilitates the elimination of anti-nutrient factors, resulting in products that are in a dry state with typically low water activity (aw), which do not require refrigeration storage. Such products are suitable for a tropical region like Africa where infrastructure for a cold supply chain is inadequate (Filli et al., 2010).
Extrusion of foods, however, demands close control of many variables such as feed moisture, feed composition, feed particle size, feed rate, barrel temperature, screw speed, screw configuration, and die geometry. The material properties and process variables determine the extent of macromolecular transformations during the extrusion process, which in turn influence the rheological properties of the food melt in the extruder and, consequently, the product characteristics of extrudates (Meng et al., 2010).
Extrusion cooking (EC) has become an increasingly popular procedure in the cereal, snack, and ready-to-eat food categories, which utilize starchy and proteinaceous raw materials (Lins et al., 2000). Boonyasirikool and Charaunuch (2000) reported a nutritious soy snack by EC, which gained a moderately high score in texture preference and acceptance. EC has some unique features compared to other heat processes. It is capable of breaking covalent bonds in biopolymers and facilitating reactions otherwise limited by diffusion of reactants and products (Iwe et al., 2001).
Several researchers in Africa have made considerable progress in product development using extrusion technology (ET) for the development and production of traditional-based products from indigenous materials (Table 1). For some time now, interest has been shown throughout the world, especially in Africa, for the production of nutritious blended foods for all population groups with high nutritional requirements in order to tackle the problem of food and nutritional insecurity.
One of the main purposes of extrusion is to increase the variety of foods in the diet by producing a wide range of products with different shapes, textures, colors and flavors from basic ingredients. Extrusion has great potential in developing economies. Chigumira (1992) outlined the advantages of EC as follows: (1) gelatinization of starch which enhances digestibility; (2) protein denaturation enhancing digestibility; (3) inactivation of some thermally labile growth inhibitors such as trypsin inhibitors; (4) inactivation of deteriorative enzymes (lipases and oxidases) results in a product with better storage stability; (5) destruction of natural toxicants—goitrogens, haemagglutinins cynogenetic, glycosides; (6) product instantization, which can be prepared quickly, saving time and equipment; (7) reduced cooking time, thus enhancing the retention of vitamins and nutritive value of the food; (8) shelf stability of extrusion-cooked foods, thus ensuring nutritious food year-round; and (9) fuel costs associated with normal lengthy cooking are almost negligible.
Extrusion technology can make traditional products more acceptable in the fast changing global society if properly adopted for upgrading production processes. ET is particularly useful and significant when cooking or gelation is required at some point of food processing which forms a greater portion of most traditional African foods. Its use in the production of meat analogs, sausage products, animal food, pet foods, snacks, cereals, paste foods, and a series of other products has long been reported (Harper, 1979).
Properly designed convenience foods can be made through extrusion, which can influence nutritional requirements in societies where social changes are altering traditional patterns of food preparation and acceptability. Often, the fabricating process of food involves imparting cohesive qualities to materials lacking cohesiveness and EC performs this function. The resulting structure of a desired product must have a texture similar to that of the target product (i.e., it must simulate such important sensory characteristics of chewability and mouthfeel).