Cereal antinutritional factors

Nowadays, most breakfast cereals are made either by original traditional processes or by using alternative extrusion methods. Commercial flakes, shreds, and oven-puffed cereals could be alternatively manufactured via extrusion. There are two major types of extrusion processes cold and thermoplastic. Cold extrusion is almost exclusively applied for production of pasta products (Chapter 10), whereas thermoplastic extrusion is used for manufacturing breakfast cereals and snack foods (Chapter 12). Undoubtedly, the most popular and versatile extrusion process is thermoplastic, defined as the combination of heat and mechanical shear to enhance starch gelatinization and dextrinization, protein denaturation, and inactivation of microorganisms, enzymes, and antinutritional factors. The changes in the properties of the starch and proteins result in the formation of a plastic material that could be formed and/or restructured into desired configurations. 

FIGURE 17.5 Chemical structure of antinutritional factors associated with some cereal grains, (a) Cyanogenic glucosides. (b) Goitrogens. 

In addition to the starch properties already described, several starchy foods (for instance, cereals and legumes) have antinutritional factors, such as lectins, tannins, phytates, and enzyme inhibitors (both protease and amylase inhibitors). Amylase inhibitors present in raw pulses may reduce the activity of amylase in the human small intestine. However, most of these factors, especially enzyme inhibitors, are inactivated during food processing and cooking. 

Plant protein sources provide 65% of the world s supply of protein, with cereal grains (47%) and pulses, nuts and oilseeds (8%) as the other major sources. Of the cereals, wheat (43%), rice (39%) and maize (12%) are the main contributors. Other limited sources of plant protein are fruits, leaves, tubers and other parts of plants included under the terms fruits, vegetables or root crops. Plant protein sources can differ from animal protein sources in terms of digestibility, amino acid composition, the presence of antinutritional (such as enzyme inhibitors) and toxic factors (e.g. saponins, cyanogens and lectins), which adversely influence protein digestibility, nutritional value and food safety. 

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