CHEMICAL COMPONENTS 71 subsequent relaxation of the tension). In general factor. Too low a gliadin content leads to inhibi- the sulphur-containing cysteine residues occur in tion of bubble expansion while the reverse results the a-helical regions, so that the disulphide bonds in excessive expansion and collapse form between these regions in adjacent polypep- Gliadin complements are characteristic of tides. B-Turns thus remain unencumbered by individual cultivars and these, revealed through nterchain bonds that might otherwise restrict polyacrylamide gel electrophoresis(PAGe),are eights of glutenins exploited in establishing the varietal identity of ire up wheat cultivars(Fig. 3. 14)and for detecting The unusually high content of the amino acids adulteration of T, durum products with Taestium asparagine and glutamine found in gluten pro- additions teins may be significant in providing stability While this technique may be useful in other of gluten, through their tendency to become species also, it has not been developed to the sa nvolved in hydrogen bonding. Hydrophobic and degree as in wheat. An even more sensitive electrostatic reactions associated with other method of identifying protein components is high amino acid side chains also contribute performance liquid chromatography(HPLC).It he relative importance of glutenins and gliadins is faster, and capable of greater resolution than varies in wheats from different parts of the world. PAGE. Its widespread use is limited by its greater In australian and italian wheats gliadin variations expense and demands for technical expertise have the strongest association with bread quality subunits with apparent molecular weight of High lysine mutants To produce cereals with better balanced pro- Each wheat possesses a complement of 3-5 types, teins, from a nutritional point of view, breeders nd a variety of individual subunits(allelic forms) have exploited mutants with high lysine and high may represent each type, giving rise to variation arginine contents. It is the storage proteins that in baking properties. Gliadins are thought to are deficient in these amino acids so the mutants behave as plasticizers, the proportional relation- selected frequently achieve the improved balance ship between them and glutenins is an important through a deficiency in storage proteins(hoseney and Variano-Marston, 1980). In the ' opaque' varieties of maize high lysine content is associated with° opaque(o2) and floury(组2) genes being double recessive, and the consequent inhibition of zein synthesis(Watson, 1987)(cf. Ch. 4). Thus the high lysine'varieties of maize, barley sorghum and pearl millets have lower yields than their conventional counterparts ds have been defined as those substances 月目上 soluble in 2. soluble in organic solvents such as chloroform ether or benzene 3. contain long chain hydrocarbon groups in FIG 3 14 PAGE their molecules, and gliadin patterns of four U.K. wheat varieties. Courtesy of 4. are present in or derived from living organismsCHEMICAL C subsequent relaxation of the tension). In general the sulphur-containing cysteine residues occur in the a-helical regions, so that the disulphide bonds form between these regions in adjacent polypep￾tides. f3- Turns thus remain unencumbered by interchain bonds that might otherwise restrict their extension. Molecular weights of glutenins are upward of 105. The unusually high content of the amino acids asparagine and glutamine found in gluten pro￾teins may be significant in providing stability of gluten, through their tendency to become involved in hydrogen bonding. Hydrophobic and electrostatic reactions associated with other amino acid side chains also contribute. The relative importance of glutenins and gliadins varies in wheats from different parts of the world. In Australian and Italian wheats gliadin variations have the strongest association with bread quality. In European wheats high molecular weight glutenin subunits with apparent molecular weight of 90-150 K are paramount in determining quality. Each wheat possesses a complement of 3-5 types, and a variety of individual subunits (allelic forms) may represent each type, giving rise to variation in baking properties. Gliadins are thought to behave as plasticizers, the proportional relation￾ship between them and glutenins is an important Beaver I Ri band I Hereward I Mercia FiG 3.14 PAGE electrophoretogram showing distinctive gliadin patterns of four U.K. wheat varieties. Courtesy of FMBRA, Chorleywood, England. Lipids Lipids have been defined as those substances which are: 1. insoluble in water , 2. soluble in organic solvents such as chloroform, ether or benzene, 3. contain long chain hydrocarbon groups in their molecules, and 4. are present in or derived from living organisms (Kates, 1972). OMPONENTS 71 factor. Too Iowa gliadin content leads to inhibi￾tion of bubble expansion while the reverse results in excessive expansion and collapse. Gliadin complements are characteristic of individual cultivars and these, revealed through polyacrylamide gel electrophoresis (PAGE), are exploited in establishing the varietal identity of wheat cultivars (Fig. 3.14) and for detecting adulteration of T. dwum products with T. aestivum additions. While this technique may be useful in other species also, it has not been developed to the same degree as in wheat. An even more sensitive method of identifying protein components is high performance liquid chromatography (HPLC). It is faster, and capable of greater resolution than PAGE. Its widespread use is limited by its greater expense and demands for technical expertise. High lysine mutants To produce cereals with better balanced pro￾teins, from a nutritional point of view, breeders have exploited mutants with high lysine and high arginine contents. It is the storage proteins that are deficient in these amino acids so the mutants selected frequently achieve the improved balance through a deficiency in storage proteins (Hoseney and Variano-Marston, 1980). In the 'opaque' varieties of maize high lysine content is associated with 'opaque' ( oz) and 'floury' (flz) genes being double recessive, and the consequent inhibition of zein synthesis (Watson, 1987) (cf. Ch. 4). Thus the 'high lysine' varieties of maize, barley, sorghum and pearl millets have lower yields than their conventional counterparts