Preface Orange growers would love to be able to grow navel oranges as both a fresh produce crop and as a juice crop. Navel oranges are seedless, large, easy to peel, and can withstand mechanical harvesting and packaging—a favorite of fresh fruit consumers all over the world. Unfortunately, navel orange juice has a problem. Although it tastes just fine when it is freshly squeezed from the fruit, it will turn bitter in a few hours at ambient temperature, overnight when refrigerated. This "delayed bitterness" problem has been the target of a number of research efforts in the United States, Australia, Japan, Israel, Spain, Italy, China, Brazil, and other areas where citrus is grown as a commercial crop. We have learned a great deal about the limonoids, the chemical constituents responsible for delayed bitterness in citrus fruits, during the past 40 years. Much of the chemistry and biochemistry of limonoids has been elucidated, and a number of chromatographic techniques have been developed to lower the bitter limonoid levels in citrus juices. However, as the research went forward on limonoids it was discovered that these compounds have interesting biological functionality in both the plants and the animals that consume them. Thus we stand at an interesting horizon, research is expanded to determine how these compounds function in the human diet. It may well prove that diets rich in citrus limonoids may prevent or deter the development of certain types of cancers. This book is the first volume to bring together all the aspects of research on citrus limonoids—the chemistry, analysis, biochemistry, and biological activities. It will be of interest to the citrus industry, the food industry, the pharmaceutical industry, the health care industry, and to the general public. Much of the work presented in this book was initiated by the many collaborators working with Dr. Shin Hasegawa and his research group. During the course of Dr. Hasegawa's biochemical research on limonoids in Pasadena, there were three major breakthroughs. First was the isolation of several species of bacteria that are capable of metabolizing limonoids. The biochemical conversion of citrus limonoids was first demonstrated in bacteria and five biodégradation pathways were established. These findings had significant contribution to elucidation of biosynthetic pathways of limonoids in Citrus. The second breakthrough was the discovery that the stems of lemon seedlings were an excellent tool for the preparation of C-labeled limonoid substrates for radioactive tracer work, which were required for the study of the biosynthetic pathways of these compounds. The third breakthrough was the most important of all—the discovery that citrus plants have a natural debittering process that converts the limonoid aglycones to non-bitter limonoid glucosides during the final stages of fruit maturation. For 25 years, Dr. Hasegawa was part of the staff at the U.S. Department of Agriculture (USDA), Agricultural Research Service, Fruit and Vegetable Laboratory in Pasadena, California, where much of his work on the biochemistry of limonoid accumulation was conducted. 14
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The USDA Fruit and Vegetable Chemistry Laboratory: a Brief History In 1910 the Citrus By-Products Laboratory was established by the Chemistry Bureau of the U S D A on South Mission Road in Los Angeles at the request of the California Fruit Growers Exchange (now Sunkist Growers). The name was changed to the Los Angeles Fruit and Vegetable Chemistry Laboratory in 1921. The research group at this laboratory worked on projects aimed at evaluating and enhancing citrus products: juice, vinegar, butter, preserved peel products, and concentrates. The Citrus By-Products research group developed the Brix:acid maturity tests for citrus fruits that are still used today. Other early research projects included the use of ethylene gas as a greening agent; development of maturity standards for avocados, walnuts, and other fruits; dried fruit and vegetable products; determining the composition of lemon oil; and the development of the Davis colorimetric test for the measurement of flavonoid content in grapefruit juices. In 1947, a fire badly damaged part of the Los Angeles Laboratory. A new facility was built on surplus government property in Pasadena. The new building was dedicated on April 14,1949, as a field station of the Western Regional Research Laboratory in Albany, California. A number of significant projects have originated here including the invention of modern thin-layer chromatography, the characterization of citrus flavonoids, the development of dihydrochalcone sweeteners, the discovery of a new class of plant biochemical regulators, and the elucidation of the chemistry and biochemistry of citrus limonoid bitter principles. The Fruit and Vegetable Chemistry Laboratory maintained a strong association with the citrus processing industry. Several industrial groups have financed the positions of scientists at the Laboratory, including the Desert Grapefruit Industry Board, Diamond Nut Growers Association, the California Lima Bean Association, the Date Administrative Committee, and the Citrus Advisory Board. By far the most enduring collaboration was with the Citrus Products Technical Committee, which first began supporting research as the Lemon Advisory Board (originally called the Lemon Products Technical Committee) in 1955. In February of 1994, the President proposed the closure of the Pasadena laboratory, along with several other U S D A research facilities. The Pasadena lab was officially closed in November of 1994, ending a long and successful research program. We dedicate this book to the many scientists and staff who worked with us at the Fruit and Vegetable Chemistry Laboratory, especially those involved in the research efforts on natural products found in Citrus: Dr. Vincent Maier, Dr. Raymond Bennett, Dr. Robert Horowitz, Dr. David Dreyer, Dr. Henry Yokohama, Carl Vandercook, Dr. John Manthey, Dr. Brent Tisserat, Dr. Katherine Kanes, Dr. James Keithley, Dr. Jean Hsu, Zareb Herman, Chi Fong, Peter Ou, Jerry Klavons, E d Orme, Dora Smolensky, Linda Brewster, Grace Choi, Sadie Vannier, and Karen Kwan.
Acknowledgments We thank all of our contributing authors who graciously provided their time and effort to provide excellent presentations at the symposium and to write the chapters for this book. The symposium could not have been held without the sponsorship and support of the American Chemical Society Division of Agricultural and Food Chemistry, and the financial
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support of Cargill, Inc., Minneapolis, Minnesota, and the Florida Department of Citrus, Lake Alfred, Florida M A R K A . BERHOW National Center for Agricultural Utilization Research Agricultural Research Service U.S. Department of Agriculture 1815 North University Street Peoria, IL 61604
[email protected] SHIN HASEGAWA Western Regional Research Center Agricultural Research Service U.S. Department of Agriculture 800 Buchanan Street Albany, C A 94710
[email protected] G A R Y D . MANNERS Western Regional Research Center Agricultural Research Service U.S. Department of Agriculture 800 Buchanan Street Albany, C A 94710
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