CHEMICAL COMPONENTS proteins of wheat starch to have molecular masses of water available during cooking. Digestibilit of under 50 k while integral proteins were over in the intestines of single-stomached animals is 50 K. Altogether ten polypeptides have been also increased by gelatinization separated between 5 K and 149 K. The major 59 K polypeptide is probably the enzyme respon- Gelatinization sible for amylose synthesis. It has been shown to be concentrated in concentric shells within This is a phenomenon manifested as several granules. Two other polypeptides of 77 K and changes in properties, including granule swelling 86 K are likely to be involved in amylopectin and progressive loss of organized structure synthesis. Perhaps the most interesting of the(detected as loss of birefringence and crystallinity), surface proteins is that in the 15 K band. increased permeability to water and dissolved This has been found in greater concentration or bstances (including dyes), increased leaching starches from cereals with soft endosperm than of starch components, increased viscosity of the on those from cereals with hard endosperm. The aqueous suspension and increased susceptibility protein has been called friabilin,, because of its to enzymic digestic association with a friable endosperm(cf Ch. 4) At room temperature starch granules are not (Greenwell and Schofield, 1989) totally impermeable to water, in fact water uptake Phosphorus is another important minor con- can be detected microscopically by a small increase stituent of cereal starches. It occurs as a com- in diameter. The swelling is reversible and the onent of lysophospholipids. They consist of 70% wetting and drying can be cycled repeatedly lysophosphatidyl choline, 20% lysophosphatidyl without permanent change. If the temperature of ethanolamine and 10% lysophosphatidyl glycerol. a suspension of starch in excess water is raised The proportion of lysophospholipids to free fatty progressively, a condition is reached, around acids varies with species: in wheat, rye, triticale 60C, at whic ible swelling begins, and and barley over 90%occurs as lysophospholipids, continues with increasing temperature. The in rice and oats 70% and in millets and sorghum change is endothermic and can be quantified by 55%. In maize 60% occurs as free fatty acids thermal analysis techniques Removal of lipids from cereal starches reduces starch are: wheat 19.7, maize 18.0, waxy majay (Morrison, 1985) Typical heats of gelatinization in J per g of he temperatures of gelatinization-related changes 19.7 and high amylose maize 31.79(Maurice et and increases peak viscosity of pastes. In other al. 1983). Swelling involves increased uptake of words they become more like the lipid-free potato water and can thus lead to increased viscosity by reducing the mobile phase surrounding the gran ules; accompanying leaching of starch polymers Technological importance of starch into this phase can further increase viscosity. The swelling behaviour of starch heated in water is Much of the considerable importance of starch often followed using a continuous automatic in foods depends upon its nutritional properties; viscometer, such as the Brabender Amylograph it is a major source of energy for humans and for ( Shuey and Tipples, 1980). Upon heating a slurry domestic herbivorous and omnivorous animals. of 7-10% starch w/w in water at a constant rate In the human diet it is usually consumed in a of 10-5C per min, starch eventually gelatinizes cooked form wherein it confers attractive textural and begins to thicken the mixture The tempera qualities to recipe formulations. These can vary ture at which a rise in consistency is shown is from those of gravies and sauces, custards and called the pasting temperature. The curve then pie fillings to pasta, breads, cakes and biscuits generally rises to a peak, called the peak viscosity (cookies). Much of the variation in texture depends When the temperature reaches 95C, that tem upon the degree of gelatinization, which in turn perature is maintained for 10-30 min and stirring depends upon the temperature, and the amount is continued to determine the shear stability ofCHEMICAL COMPONENTS 61 proteins of wheat starch to have molecular masses of water available during cooking. Digestibility of under 50 K while integral proteins were over in the intestines of single-stomached animals is 50 K. Altogether ten polypeptides have been also increased by gelatinization. separated between 5 K and 149 K. The major Gelatinization 59 K polypeptide is probably the enzyme respon￾sible for amylose synthesis. It has been shown to be concentrated in concentric shells within This is a phenomenon manifested as several granuies. Two other polypeptides of 77 K and changes in properties, including granule swelling 86 K are likely to be involved in amylopectin and progressive loss of organized structure synthesis. Perhaps the most interesting of the (detected as loss of birefringence and crystallinity), surface proteins is that in the 15 K band. increased permeability to water and dissolved This has been found in greater concentration on substances (including dyes), increased leaching starches from cereals with soft endosperm than of starch components, increased viscosity of the on those from cereals with hard endosperm. The aqueous suspension and increased susceptibility protein has been called 'friabilin', because of its to enzymic digestion. association with a friable endosperm (cf Ch. 4) At room temperature starch granules are not (Greenwell and Schofield, 1989). totally impermeable to water, in fact water uptake Phosphorus is another important minor con- can be detected microscopically by a small increase stituent of cereal starches. It occurs as a com- in diameter. The swelling is reversible and the ponent of lysophospholipids. They consist of 70% wetting and drying can be cycled repeatedly lysophosphatidyl choline, 20% lysophosphatidyl without permanent change. If the temperature of ethanolamine and 10% lysophosphatidyl glycerol. a suspension of starch in excess water is raised The proportion of lysophospholipids to free fatty progressively, a condition is reached, around acids varies with species: in wheat, rye, triticale 60"C, at which irreversible swelling begins, and and barley over 90% occurs as lysophospholipids, continues with increasing temperature. The in rice and oats 70% and in millets and sorghum change is endothermic and can be quantified by 55%. In maize 60% occurs as free fatty acids thermal analysis techniques. (Morrison, 1985). Typical heats of gelatinization in J per g of dry Removal of lipids from cereal starches reduces starch are: wheat 19.7, maize 18.0, waxy maize the temperatures of gelatinization-related changes 19.7 and high amylose maize 31.79 (Maurice et and increases peak viscosity of pastes. In other al., 1983). Swelling involves increased uptake of words they become more like the lipid-free potato water and can thus lead to increased viscosity by starch. reducing the mobile phase surrounding the gran￾ules; accompanying leaching of starch polymers into this phase can further increase viscosity. The swelling behaviour of starch heated in water is Technological importance of starch Much of the considerable importance of starch often followed using a continuous automatic in foods depends upon its nutritional properties; viscometer, such as the Brabender Amylograph it is a major source of energy for humans and for (Shuey and Tipples, 1980). Upon heating a slurry domestic herbivorous and omnivorous animals. of 7-10% starch w/w in water at a constant rate In the human diet it is usually consumed in a of 1°-5"C per min, starch eventually gelatinizes cooked form wherein it confers attractive textural and begins to thicken the mixture. The tempera￾qualities to recipe formulations. These can vary ture at which a rise in consistency is shown is from those of gravies and sauces, custards and called the pasting temperature. The curve then pie fillings to pasta, breads, cakes and biscuits generally rises to a peak, called the peak viscosity. (cookies). Much of the variation in texture depends When the temperature reaches 95"C, that tem￾upon the degree of gelatinization, which in turn perature is maintained for 10-30 min and stirring depends upon the temperature, and the amount is continued to determine the shear stability of