Levels of Protein and Protein Composition in Hard Winter Wheat Flours and the Relationship to Breadmaking

Cereal Chem. 83(4):418–423 Protein and protein fractions were measured in 49 hard winter wheat flours to investigate their relationship to breadmaking properties, particularly loaf volume, which varied from 760 to 1,055 cm and crumb grain score of 1.0–5.0 from 100 g of flour straight-dough bread. Protein composition varied with flour protein content because total soluble protein (SP) and gliadin levels increased proportionally to increased protein content, but albumins and globulins (AG), soluble polymeric proteins (SPP), and insoluble polymeric protein (IPP) levels did not. Flour protein content was positively correlated with loaf volume and bake water absorption (r = 0.80, P < 0.0001 and r = 0.45, P < 0.01, respectively). The percent SP based on flour showed the highest correlation with loaf volume (r = 0.85) and low but significant correlation with crumb grain score (r = 0.35, P < 0.05). Percent gliadins based on flour and on protein content were positively correlated to loaf volume (r = 0.73, P < 0.0001 and r = 0.46, P <0.001, respectively). The percent IPP based on flour was the only protein fraction that was highly correlated (r = 0.62, P < 0.0001) with bake water absorption followed by AG in flour (r = 0.30, P < 0.05). Bake mix time was correlated positively with percent IPP based on protein (r = 0.86) but negatively with percent SPP based on protein (r = –0.56, P < 0.0001). Proteins have long been known as the unique component in wheat responsible for its breadmaking quality. Wheat flour proteins can be divided into two broad groups, the gluten and nongluten proteins. Nongluten proteins include primarily albumins and globulins (AG), which are considered mainly metabolic proteins but may have some role in breadmaking (Hoseney et al 1969a). Gluten proteins (gliadins and glutenins) have been recognized as the major components responsible for variations in breadmaking characteristics. Gliadin proteins have little resistance to extension and are mainly responsible for the cohesiveness of dough, whereas glutenin proteins give dough resistance to extension (Dimler 1965; Hoseney 1992; Uthayakumaran et al 2000). Wheat proteins can also be classified based on molecular size, either polymeric or monomeric proteins. Polymeric proteins include mainly glutenins with minor amounts of high molecular weight AG, whereas monomeric proteins are gliadins with low molecular weight AG (MacRitchie 1992). Many studies have attempted to relate wheat proteins to breadmaking quality (Bushuk 1985; Hoseney and Rogers 1990; MacRitchie 1992; Borneo and Khan 1999; Toufeili et al 1999; Uthayakumaran et al 1999; Wooding et al 1999; Khatkar et al 2002a,b; Tronsmo et al 2002; Cuniberti et al 2003). Pioneering work in this area was reported by Finney and Barmore (1948), who found bread loaf volume in hard red winter and spring wheat cultivars grown at several regions was related to protein quantity. Later, Finney and Yamazaki (1967) and Finney (1984) stated that both quantity and quality of proteins affected breadmaking properties such as mixing time, tolerance, dough handling properties, water absorption, oxidation requirements, loaf volume, and crumb characteristics of bread. Recent research has been conducted to understand the role of wheat proteins in breadmaking quality, especially with regards to the large polymeric wheat proteins and dough strength (MacRitchie 1992; Wooding et al 1999; Cuniberti et al 2003). However, there is still debate as to the role of the various protein classes on breadmaking parameters such as absorption, mixing, loaf volume, and crumb grain. For example, gliadin proteins have been reported to be highly related to loaf volume by many researchers (Hoseney et al 1969a,b; Finney et al 1982; Branlard and Dardevet 1985; Weegels et al 1994; Khatkar et al 2002a,b). Others, however, have observed that gliadin proteins have an insignificant effect on loaf volume and that the glutenin proteins are the major components responsible for loaf volume (MacRitchie 1978, 1985; MacRitchie et al 1991; Gupta et al 1992; Borneo and Khan 1999; Toufeili et al 1999; Uthayakumaran et al 1999). Labuschagne et al (2004) also found that fractions with mainly gliadins negatively affect important quality traits. Large polymeric to monomeric protein ratio was related to better baking qualities. Many studies have been conducted to relate dough strength or loaf volume with protein content or protein composition as a separate research object. However, limited research has been conducted to explain the effects of changes in protein content and composition together on breadmaking parameters such as water absorption and mix time requirements, loaf volume, and crumb grain. The objectives of this research were three-fold: to investigate the relationship between flour protein content and protein composition in hard winter wheat flours; to find individual effects of protein subclasses; and to find overall effects of flour protein content and protein composition on breadmaking parameters. MATERIALS AND METHODS Samples Forty-nine hard winter wheats were provided by the U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), Grain Marketing and Production Research Center (GMPRC), Hard Winter Wheat Quality Laboratory, Manhattan, KS. Eight wheats were from the North Central Plains of the Northern Regional Performance Nursery, including SD94149, Jagger, Crimson, SD94241, SD94227, Tandem, Rose, and SD 93528. Forty-one wheats were from the Southern Regional Performance Nursery, including W94-245, OK94P549, W94-137, T89, W94-042, W94320, W94-435, and T93 from the North Central Plains; W94-042, OK94P461, PI495594, NE93405, NE93427, XH1881, T93, NE93496, G1594, and G1720 from the North High Plains; W94042, KS84W063-9-39-3MB, W94-435, T89, CO920696, NE93496, 1 Cooperative investigations, U.S. Department of Agriculture, Agricultural Research Service, and the Department of Grain Science and Industry, Kansas State University. Contribution No. 06-76-5 from the Kansas Agricultural Experiment Station, Manhattan, KS 66506. 2 USDA-ARS, Grain Marketing and Production Research Center, Manhattan, KS 66502. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. 3 Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506. 4 Corresponding author. Phone: 785-776-2708. Fax: 785-537-5534. E-mail: seokho.