INTRODUCTION
Essential oil plants and culinary herbs include a broad range of plant species that are used for their aromatic value as flavorings in foods and beverages and as fragrances in pharmaceutical and industrial products. Essential oil plants derive from aromatic plants of many genera distributed worldwide. In the United States, the most economically important sources of domestically produced essential oils are industrial by-products from citrus, balsam fir, pine, and cedarwood (Table 1, 2) while the most important crops grown in the U.S. for essential oils are peppermint and spearmint (Table 3). Most other essential oils used in the U.S. are imported (Table 4) at an annual cost in 1988 of $150 million (USDA 1989b). A significant quantity of the essential oil imported into the U.S. is further processed for export along with domestically produced oil (Table 5).
Culinary herbs aTable 6). Recent estimates by the USDA Foreign Agricultural Service reported that more than $349 million of dried condiments, seasonings, and flavorings (Table 4) and $20 million of spice oleoresins were imported into the U.S. in 1988 (USDA 1989a). A significant amount of selected herbs are domestically produced for the dried spice or condiment market Domestic production of these and other herbs and spices now imported is increasing for both processing and fresh market.re herbaceous aromatic plants grown and marketed fresh or dried and include many of the same aromatic plants which are grown for their extractable essential oils. Significant quantities of dried culinary herbs are imported annually into the U.S. (
The objectives of this paper are to provide an overview to the plants which are processed in the U.S. for essential oils and to identify fresh culinary herbs that are or can be grown in the continental U.S. The potential opportunities and constraints for production of these new crops in American agriculture will be highlighted.
ESSENTIAL OILS
Chemistry and Extraction of Essential Oils
The recovery of nonvolatile essential oils are also obtained by solvent extraction although the process is more difficult and complex than the recovery of the volatiles. This process yields an aromatic resinous product known as an oleoresin, which is more concentrated than an essential oil and which has wide application in the food industry (Heath 1981).
Essential Oils as Industrial By-products
Although a primary focus of this review is to highlight aromatic plants and culinary herbs produced in the U.S., it is important to recognize that the largest quantities of essential oils produced in the U.S. are actually byproducts from industrial processes yielding higher value primary products. Citrus essential oils are recovered from the peel which contain the oil sacs or glands located irregularly in the outer mesocarp of the fruit (Matthews and Braddock 1987). These glands are embedded at different depths in the flavedo, the colored, outer portion of the fruit and must be removed by first rupturing the glands by pressure or mechanical rasping (Matthews and Braddock 1987).The recovery of citrus oils by mechanical expression is generally obtained by two types of commercial extractors, the FMC Citrus juice Extractor (FMC Corp.) and the Brown Extractor (Automatic Machinery Corp.) (Kealey and Kinsella 1979, Kesterson et al. 1971). Citrus oils are recovered as cold-pressed oils or as a specific constituent such a d-limonene as by-products of the juice and beverage industry and yield important aromatic and flavoring compounds used in a wide array of food, cosmetic and industrial products.
The other large quantity of essential oils produced as industrial by-products in this country comes from the wood and pulp manufacturing industries. More than 1650 tonnes of such oils, predominantly from cedarwood, are produced annually (Lawrence 1979).
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Basil oil. Sweet basil (Ocimum basilicum L.) is a popular culinary herb and a source of essential oils (ITC 1986) extracted by steam distillation from the leaves and flowering tops and used to flavor foods, in dental and oral products, and in fragrances. There are several types of basil oil on the world market European, French, or sweet basil; Egyptian; Reunion or Comoro; Bulgarian; and Java (Heath 1981). The European basil oils, considered to be the highest quality, contain methyl chavicol d-linalool and to a lesser extent 1,8-cineole, plus many other compounds (Guenther 1985, Simon et al. 1984). Egyptian basil oil is similar to the European, except that the concentration of d-linalool is lower and methyl chavicol is higher. Reunion or Comoro contains little d-linalool, but has a very high concentration of methyl chavicol (Lawrence et al. 1972, Simon et al. 1984). Bulgarian basil oil is rich in methyl-cinnamate and Java basil oil is rich in eugenol (Heath 1981). From an evaluation of the entire USDA collection plus other commercial and wild sources, we observed a wide range of chemical variation within O. basilicum and other species (O. canum, O. sanctum, O. gratissimum, and O. kilimandscharicum). We have identified chemotypes that represent each of the commercial types of basil oil. Promising lines are being screened for chemical stability, vigor, and uniformity. The characteristics of the population has continued to improve under mass selection. Isolation blocks serve as seed sources. We are currently developing a new line rich in methyl cinnamate (Simon et al. 1990).
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