**7.2 Breakfast cereals**

Breakfast cereals (BCs) have been defined as "processed grains for human consumption". The breakfast cereal industry, in the United States, appeared at the beginning of the 20th century and has grown rapidly in the last few years, making BCs important economically viable products. Basic processes for the production of BCs include flaking, oven and gun puffing, baking, shredding and direct expansion (extrusion cooking). These processes convert raw and dense grains (7.7 kg/100 cm3) into friable, crunchy or chewable products, adequate for human consumption, with apparent density in the range of 0.6 to 1.6 kg/100 cm3 (Fast, 2000). Thermoplastic extrusion presents various advantages over the conventional processes used for BC production, such as shorter processing times and lower costs; less physical space necessary; greater flexibility for the production of a variety of products, simply changing the die, process conditions, initial formulation and final enrobing of the product, and particle size of the raw material (Huang, 1998; Bailey et al., 1991; Riaz, 2000).

The most commonly used cereals in extruded BC formulations are rice, wheat, oats and corn (Fast, 2000; Riaz, 2000). In the formulation of extruded BCs, a mixture of these cereals can be used, in the form of flours, grits or whole grain flours, and they can also be mixed with other ingredients such as starches, sugar, salt, malt extract or other liquid sweeteners, heat stable vitamins and minerals, flavourings, colorants and water, to vary appearance, texture, taste, aroma and other product characteristics (Riaz, 2000).

To produce BCs by extrusion cooking two different processes can be used: (i) pellet or shred production for manufacturing cereals such as cornflakes or shredded cereals with additional laminating and toasting processes after extrusion cooking, and (ii) directly expanded cereals production. Extruded flakes can be obtained by adding a blend of grains (flour, starches, etc.) and liquids (water, sweetener, colorants, etc.) directly to the extruder. The blend is forced through the barrel, where heat is applied to cook the dough, and then the product passes through a cooling section to prevent expansion, obtaining pellets after the die. Then the pellets pass through an equipment to be flaked and toasted. The process to obtain shredded cereals is similar to that of the flake process, with the exception that pellet sizes are not as critical, because they will be shredded without additional drying and tempering. Finally, the manufacturing process for extruded, puffed or expanded BCs follows the same steps, differing only at the end of the extruder, when the dough passes through a die that is

Second generation snacks or expanded snacks, where most extruded snacks are classified, are usually low in bulk density and are often marketed as high-fibre, low-calorie, highprotein and nutritional products (Lazou & Krokida, 2011). Different raw materials used to produce these kinds of snacks (i.e. flours and/or cereals and tubers starches and proteins) are processed in a extruder resulting in a continuous mass, that is cut into pieces of uniform

Third generation snacks or pellets are normally called "half products". These snacks are produced almost the same way as second generation snacks, however, when the product exits the extruder, it has the form of the die, that is, it is not expanded, being dried in this form. The expansion of the product occurs afterwards through frying, heating by hot air or in a microwave oven (Riaz, 2000; Carvalho et al., 2009). This kind of product presents a low moisture content (between 7 and 10%), high density and stability to be stored for a long time

Breakfast cereals (BCs) have been defined as "processed grains for human consumption". The breakfast cereal industry, in the United States, appeared at the beginning of the 20th century and has grown rapidly in the last few years, making BCs important economically viable products. Basic processes for the production of BCs include flaking, oven and gun puffing, baking, shredding and direct expansion (extrusion cooking). These processes convert raw and dense grains (7.7 kg/100 cm3) into friable, crunchy or chewable products, adequate for human consumption, with apparent density in the range of 0.6 to 1.6 kg/100 cm3 (Fast, 2000). Thermoplastic extrusion presents various advantages over the conventional processes used for BC production, such as shorter processing times and lower costs; less physical space necessary; greater flexibility for the production of a variety of products, simply changing the die, process conditions, initial formulation and final enrobing of the product, and particle size of the raw material (Huang, 1998; Bailey et al., 1991; Riaz, 2000). The most commonly used cereals in extruded BC formulations are rice, wheat, oats and corn (Fast, 2000; Riaz, 2000). In the formulation of extruded BCs, a mixture of these cereals can be used, in the form of flours, grits or whole grain flours, and they can also be mixed with other ingredients such as starches, sugar, salt, malt extract or other liquid sweeteners, heat stable vitamins and minerals, flavourings, colorants and water, to vary appearance, texture, taste,

To produce BCs by extrusion cooking two different processes can be used: (i) pellet or shred production for manufacturing cereals such as cornflakes or shredded cereals with additional laminating and toasting processes after extrusion cooking, and (ii) directly expanded cereals production. Extruded flakes can be obtained by adding a blend of grains (flour, starches, etc.) and liquids (water, sweetener, colorants, etc.) directly to the extruder. The blend is forced through the barrel, where heat is applied to cook the dough, and then the product passes through a cooling section to prevent expansion, obtaining pellets after the die. Then the pellets pass through an equipment to be flaked and toasted. The process to obtain shredded cereals is similar to that of the flake process, with the exception that pellet sizes are not as critical, because they will be shredded without additional drying and tempering. Finally, the manufacturing process for extruded, puffed or expanded BCs follows the same steps, differing only at the end of the extruder, when the dough passes through a die that is

size, being afterwards dried, flavoured and stored (Booth, 1990).

without microbial damage (Carvalho et al., 2009).

aroma and other product characteristics (Riaz, 2000).

**7.2 Breakfast cereals** 

designed to allow expansion after leaving the extruder because the moisture in the formula (whether natural or added) is released from a zone of elevated temperature and pressure to ambient conditions. The die holes control the shape of the finished cereal pieces, once they are cut with a rotating knife on the outer face of the die. The extruded products can be sugar-coated or coloured and flavoured to produce a variety of products for various tastes (Fast, 2000; Eastman et al., 2001). In expanded extruded products two important characteristics are expansion and texture. Extruded products are characterized for their expansion and usually maximum expansion is desired for expanded extruded snack products. For expanded extruded breakfast cereals a different structure is desired. It is necessary to obtain products with higher apparent density, lower porosity and thicker cell walls, as these products will be immersed in an aqueous medium, such as milk, and must maintain their texture during the longest time possible, absorbing the lowest quantity of moisture possible (Collona et al., 1998).

BCs can be considered protein sources (even though cereal proteins are incomplete due to limiting essential amino acids such as lysine), as they are often formulated with various different types of cereals and consumed with milk. When produced with whole grain flours, they can be considered sources of fatty acids and fibres. Breakfast cereals are sources of vitamins and minerals, as grains contain significant amounts of B-group vitamins, tocopherols, and minerals such as iron, zinc and copper, apart from being normally consumed with milk or yoghurt, considered important sources of calcium (Jones, 2001).

Nowadays, the development of new products in the BC segment aims at the production of breakfast cereals with a functional appeal. Recent research reports the use of antioxidants such as tocopherol and lycopene (Paradiso et al., 2008; Dehghan-Shoar et al., 2010) and fibres, such as β-glucans, gums and oat, wheat and passion fruit brans (Holguín-Acuña et al., 2008; Vernaza et al., 2010; Yao et al., 2011; Ryan et al., 2011).

#### **7.3 Meat analogues**

To human diets, especially those of vegetarians, the ingestion of high protein content products has been incorporated, including, for example, meat extenders and meat analogues, obtained through the extrusion process of vegetable proteins, resulting in a product with appearance and texture similar to the fibrilar structure of meat (Strahm, 2006; Macdonald et al., 2009). Meat extenders are obtained by thermoplastic extrusion at low moisture contents (20-35%) and meat analogues are obtained by thermoplastic extrusion at high moisture contents (50-70%). The raw materials commonly used to produce meat extenders are defatted soy flour and soy protein concentrate (SPC), whereas for the production of meat analogues, soy protein concentrate (SPC) and soy protein isolate (SPI) are used.

Amongst the main vegetable proteins used to produce meat analogues are proteins from legumes such as soybeans, common beans and peas, and from cereals, especially wheat proteins responsible for the formation of the gluten network (Riaz, 2000; Strahm, 2006).

The use of raw materials with high protein contents in extrusion began around the 1970s, with the use of soy for the production of texturized soy protein and meat analogues. Although researchers agree that, during extrusion of high protein content raw materials, denaturation, melting and alignment during mass flow occur, there is still a need to understand the physicochemical and rheological changes involved, once the phenomena that lead to the

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Denaturation during the extrusion process of proteins results in a reduction of protein solubility, favours digestibility and inactivates antinutritional factors. Also, the extrusion of soy protein eliminates and/or reduces the bitter taste and the undesirable aroma and volatiles related to this protein (Areas, 1992; Kitabatake & Doi, 1992).
