Okkyung Kim Chung (Retired), Grain Marketing and Production Research Center, USDA, Agricultural Research Service, Manhattan, Kansas; Jae-Bom Ohm, Northern Crop Science Laboratory, USDA, Agricultural Research Service, Fargo, North Dakota; M. S. Ram (Retired) and Seok-Ho Park, Grain Marketing and Production Research Center, USDA, Agricultural Research Service, Manhattan, Kansas; Crispin A. Howitt, CSIRO Plant Industry, Canberra ACT 2601, Australia
WHEAT: Chemistry and Technology, Fourth Edition
Pages 363-399
DOI: https://doi.org/10.1094/9781891127557.010
ISBN: 978-1-891127-55-7
Abstract
Lipids in wheat or wheat flour are a minor constituent, and yet they play major roles in wheat production, storage, processing, products, nutrition, and consumer acceptance of finished goods (Chung and Ohm 1997). The topics of quantification and composition of lipids in wheat kernels, their structural parts, and even the processed product, i.e., flour, have been the focus of many researchers, especially the role of lipids in wheat-product quality. The studies between the mid-1960s and the 1980s made extensive use of the techniques of defatting flour and reconstituting the flour by adding back the removed lipids. This research concentrated mainly on “free lipids” (FL), i.e., lipids easily extractable with relatively nonpolar solvents, which would not disrupt the binding between lipids and other constituents such as proteins or carbohydrates. Until the late 1970s and the beginning of the 1980s, most researchers referred to the wheat or flour lipids as “nonstarch lipids” (NSL). The presence of phospholipids (PL) in starch granules was suspected due to the presence of phosphorus in highly purified starch granules. However, starch lipids (SL) could not be extracted with any solvent system at ambient temperature.
Therefore, the terminology of wheat or flour lipids is greatly dependent on the extraction conditions, including the extractants (solvents), extracting temperature, moisture contents, or extraction and quantification methodology. In addition, because lipids are unevenly distributed in wheat structural parts, lipid content and composition are also affected by milling practice, i.e., flour extraction rate, various milled streams, etc. Furthermore, the growing environments as well as the genetic backgrounds of the wheat result in variations in lipid content and composition. Many abbreviated terms are used in order to simplify a complex subject (Table 10.1).
Wheat and flour lipids have been reviewed periodically (Lasztity 1966; Mecham 1971; Chung et al 1978; Morrison 1978, 1979, 1989, 1995; Pomeranz and Chung 1978; Chung and Pomeranz 1981; Berger 1982, 1983; Pomeranz 1985, 1988b; Chung 1989, 1991; Chung and Ohm 1997, 2000; Marion and Clark 2000; Nebesny et al 2002; Day and Vu 2004). Especially, earlier research efforts were well summarized and reviewed by Mecham (1971) and Morrison (1988a) in the editions of Wheat: Chemistry and Technology edited by Pomeranz and Hlynka (1971) and Pomeranz (1988a), respectively, and also by Morrison (1978). Wheat lipid content and composition were compared among classes and also with other cereal lipids (Chung 1991, Chung and Ohm 2000), and cereal lipid compositions were compared with those of oilseeds (Day 2004). Numerous enzymatic studies on lipids have been reported; the effect of lipoxygenase on the mechanical development of wheat flour was reviewed by Daniels et al (1970) and nonamylolytic enzymes were extensively reviewed by Van Eijk and Hille (1996). The subject of enzymatic effects on lipids is discussed in Chapter 11 of this book.
Our main effort focuses on newer reports since the last publication of this book in 1988. This chapter covers recent progress in lipid methodology, comprehensively reviews functional roles of wheat/flour lipids in relation to wheat product quality, and discusses genetic research on nutritional improvement by manipulating carotenoid, tocochromanol, and fatty acid (FA) contents in wheat seeds.
