Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: October 23, 2009
Publication Date: N/A
Interpretive Summary: This book chapter is comprised of ten sections that outline the role that polyphenol oxidase (PPO) plays in noodle quality, and how it affects color and appearance. White flour is the basic ingredient for noodles that are eaten all around the world, especially in East Asia, and noodle color or darkening is a major problem for Asian consumers and noodle manufacturers. Noodles may have desirable color traits such as brightness and yellow pigments, and also undesirable colors and appearances. Darkening is attributed to PPO activity, and is a crucial issue in all of the countries exporting wheat to Asia, including the U.S., Australia and Canada. Reducing or eliminating PPO-based darkening via genetic improvement is one goal and approach for reducing darkening. Recent advances in our understanding of PPO genetics will help in the development of germplasm with near-zero PPO activity.
Technical Abstract: Noodles made from wheat (Triticum aestivum L.) are major food products around the world but are especially important to the peoples and cultures of eastern Asia. As noted in other chapters, an almost limitless variety of noodle styles are manufactured in which the most important ingredient is wheat flour. Normally, white flour obtained through modern roller milling processes is used. Milling and wheat processing is a subject unto itself (Posner and Hibbs 1997). For this chapter, it is important to recognize that the basic ingredient for noodles—white flour—comes from the wheat grain, a living, biological organism, one stage in the reproductive life cycle of the plant. Like all biological organisms, wheat has genes and enzymes that allow it to grow, reproduce, and resist attack by pathogens. In wheat, polyphenol oxidase (PPO) is composed of a group of closely related enzymes that are extremely important to Asian noodle quality. Color, appearance, texture, mouth feel, and taste are all important noodle quality attributes, and all of these attributes are the result of the interplay of ingredients and processing. Color is a primary quality attribute of all noodles as noodles are ‘seen’ before they are eaten. Noodles may have desirable color traits, such as brightness and yellow pigments, as well as undesirable colors and/or appearance. In this regard, Asian noodle discoloration (Figure 1), including general darkening as well as dark spots, is unacceptable to consumers (Mares and Panozzo, 1999; Morris et al., 2000; 2002). Darkening can occur in many refined white flour products including yellow alkaline (Cantonese) and white-salted (udon) noodles that have high moisture content and are stored for longer periods of time (refrigerated doughs and batters are also subject to darkening). Conversely, darkening of wheat products is not a universal problem and may be considered a ‘non-issue’ when it comes to most baked products of the US, including the leading use of refined wheat flour – pan bread; therefore, selection for reduced darkening potential is not a priority when developing wheat cultivars for such products. Over the past three decades, the close relationship between kernel PPO activity and darkening of alkaline and white salted Asian noodles has become apparent. Developing wheat varieties with minimal discoloration is a crucial issue in all of the countries exporting wheat to Asia, including the US, Australia and Canada. The importance of this chapter and much of the research that it reviews is a direct result of the noodle darkening problem and the desire of major wheat exporting countries to better serve the needs of the Asian consumer.