BREAKFAST CEREALS AND OTHER PRODUCTS OF EXTRUSION COOKING 253 lowering effect. Rice bran was not so effective as of available lysine as maillard reaction products oat bran in lowering plasma total cholesterol, but (McAuley et al., 1987). However, lysine deficiency rice bran favourably altered the ratio of high is of less importance in ready-to-eat cereals than in density lipoprotein(HDL) to low density lipo- bread because the former are generally consumed protein(LDL), a sensitive lipid index of future with milk, which is a good source of lysine coronary heart disease(Nestel, 1990) Moreover, some ready-to-eat breakfast cereals Preliminary work indicates that the beta-glucan have a protein supplementation in the soluble fibre of a waxy, hull-less barley ultivar also has hypocholesterolaemic effects and the extracted beta-glucans from barley have Carbohydrates possible use as a fibre supplement in baked The principal carbohydrate in cereals is starch products(Klopfenstein et aL. 1987; Newman et the complete gelatinization of which is desirable al.,1989) in processed foods, such as ready-to-eat cereals Whereas ordinary cooking at atmospheric pressure Nutritive value of breakfast cereals requires the starch to have a moisture content of 35-40% to achieve complete gelatinization, th The nutritive value of breakfast cereals, as same occurs at feed moisture levels of less than compared with that of the raw materials from 20% in extrusion cooking at 110-135C(Asp and which they were made, depends very much on Bjorck, 1989; Linko 1989a). Extrusion cooking the processing treatment involved, remembering increases the depolymerization of both amylose and that all heat treatment processes cause some amylopectin by random chain splitting. The sus- modification or loss of nutrients. Thus, while ceptibility of starch to the action of alpha-amylase extrusion cooking may cause the loss of essential increased in the following sequence: steam cooking amino acids, it also inactivates protease inhibitors,(least), steam flaking, popping, extrusion cooking hereby increasing the nutritional value of the drum drying(most)(Asp and Bjorck, 1989) proteins. The chemical composition of some ready-to- eat breakfast cereals manufactured in the U. K. Calorific value s shown in Table ll The calorific value of most ready-to-eat ceres Shredded wheat, made from low protein, soft as eaten is higher than that of bread(975 kJ/100 g wheat has a protein content considerably lower 233 Cal/100 g), largely on account of the relatively than that of puffed wheat, which is made from lower moisture content of the former. Compared a high-protein hard wheat, such as durum at equal moisture contents, the difference in CWRS wheat calorific value is small. Fat and cholesterol con- tents may be lower than those of some other cereal Proteins and amino acids The processes involved in the manufacture of All cereal products are deficient in the amino ready-to-eat cereals cause partial hydrolysis of acid lysine, but the deficiency may be greater in phytic acid (cf p. 295); the degree of destruction ready-to-eat cereals than in bread because of the increases at high pressures: about 70% is destroyed changes that occur in the protein at the high in puffing, about 33% in flaking temperature treatment. The protein efficiencies of wheat-based breakfast cereals (relative to casein= 100), as determined by rat-growth trials, have been reported as: -15.3 for extrusion puffed Enzymes, which are proteins, are generally 1.8-16.3 for flaked-toasted; 2.8 for extrusion inactivated partially or completely during extru 69.9 for extruded, lightly roasted. sion cooking. Thus, peroxidase was completely The d ces were partly explained by the loss inactivated by extrusion cooking at 110%-149CofBREAKFAST CEREALS AND OTHER PRODUCTS OF EXTRUSION COOKING 253 of available lysine as Maillard reaction products (McAuley et al., 1987). However, lysine deficiency is of less importance in ready-to-eat cereals than in bread because the former are generally consumed with milk, which is a good source of lysine. Moreover, some ready-to-eat breakfast cereals have a protein supplementation. Carbohydrates The principal carbohydrate in cereals is starch, the complete gelatinization of which is desirable in processed foods, such as ready-to-eat cereals. Whereas ordinary cooking at atmospheric pressure requires the starch to have a moisture content of 3540% to achieve complete gelatinization, the same occurs at feed moisture levels of less than 20% in extrusion cooking at 1 1Oo-135"C (Asp and Bjorck, 1989; Linko 1989a). Extrusion cooking increases the depolymerization of both amylose and amylopectin by random chain splitting. The sus￾ceptibility of starch to the action of alpha-amylase increased in the following sequence: steam cooking (least), steam flaking, popping, extrusion cooking, drum drying (most) (Asp and Bjorck, 1989). calorific value The calorific value of most ready-to-eat cereals as eaten is higher than that of bread (975 kJ/100 g; 233 Ca1/100 g), largely on account of the relatively lower moisture content of the former. Compared at equal moisture contents, the difference in calorific value is small. Fat and cholesterol con￾tents may be lower than those of some other cereal foods. The processes involved in the manufacture of ready-to-eat cereals cause partial hydrolysis of phytic acid (cf. p. 295); the degree of destruction increases at high pressures: about 70% is destroyed in puffing, about 33% in flaking. Enzymes Enzymes, which are proteins, are generally inactivated partially or completely during extru￾sion cooking. Thus, peroxidase was completely inactivated by extrusion cooking at 1 10"-149°C of lowering effect. Rice bran was not so effective as oat bran in lowering plasma total cholesterol, but rice bran favourably altered the ratio of high density lipoprotein (HDL) to low density lipo￾protein (LDL), a sensitive lipid index of future coronary heart disease (Nestel, 1990). Preliminary work indicates that the beta-glucan in the soluble fibre of a waxy, hull-less barley cultivar also has hypocholesterolaemic effects, and the extracted beta-glucans from barley have possible use as a fibre supplement in baked products (Klopfenstein et al., 1987; Newman et al., 1989). Nutritive value of breakfast cereals The nutritive value of breakfast cereals, as compared with that of the raw materials from which they were made, depends very much on the processing treatment involved, remembering that all heat treatment processes cause some modification or loss of nutrients. Thus, while extrusion cooking may cause the loss of essential amino acids, it also inactivates protease inhibitors, thereby increasing the nutritional value of the proteins. The chemical composition of some ready-to￾eat breakfast cereals manufactured in the U.K. is shown in Table 11.1. Shredded wheat, made from low protein, soft wheat has a protein content considerably lower than that of puffed wheat, which is made from a high-protein hard wheat, such as durum or CWRS wheat. Proteins and amino acids All cereal products are deficient in the amino acid lysine, but the deficiency may be greater in ready-to-eat cereals than in bread because of the changes that occur in the protein at the high temperature treatment. The protein efficiencies of wheat-based breakfast cereals (relative to casein = loo), as determined by rat-growth trials, have been reported as: - 15.3 for extrusion puffed; 1.8-16.3 for flaked-toasted; 2.8 for extrusion toasted; and 69.9 for extruded, lightly roasted. The differences were partly explained by the loss