Chapter 25
Characterization of the Putrid Aroma Compounds of Ginkgo biloba Fruits Thomas H . Parliment
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General Foods USA, Technical Center, 555 South Broadway, Tarrytown, N Y 10591
The Ginkgo family of trees is represented by a single surviving species, Ginkgo biloba. It is an ancient line unlike any other living conifer and may represent a link between the conifers and the tree-ferns. In the fall female trees produce yellow-orange fruits with a thick fleshy layer surrounding an edible kernel. The odor of these fruits is described as putrid. This study identified the odorous principles as high levels of butanoic and hexanoic acids.
The Ginkgo family (Ginkgoaceae) is represented today by a single surviving species of tree, native to southeastern China. The Ginkgo biloba tree has been introduced to North America where it has become valued as a street and park tree. It represents an ancient line of tree that is unlike any other living conifer. Some believe ginkgos are a link between the conifers and the more primitive plants: the tree-ferns and cycads. Extracts of dried ginkgo leaves have been used therapeutically for centuries. The extract is semipurifed to produce a mixture of ginkgo flavone glycosides and terpenoids (ginkgolides). Ginkgolides have not been found in any other living plant and differ only in number and position of hydroxyl groups. This extract has shown value in curing cerebral and peripheral circulatory disturbances. Symptoms in elderly people said to be relieved by ginkgo treatment include difficulty in concentration, absent mindedness confusion, lack of energy, decreased physical performance, depression, anxiety and headache (1). Both male and female trees exist. Male trees are preferred because they don't produce fruits as females do and because they can grow in poor, hard-packed soil and polluted air. In the fall, female trees produce numerous fruits on their branches. (Figure 1). When mature, these circular fruits are yellow to orange in color and about 2.5 cm in diameter. The flesh surrounds a hard, tan shell that contains the green soft edible kernel of the seed. In the Far East, these seeds are roasted and eaten. The flesh of the
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25. PARLIMENT
Putrid Aroma Compounds of Ginkgo biloba Fruits 277
mature fruit gives off an aroma described as "putrid" or "foul" (2). The presence of these fruits is the main reason that female trees are considered undesirable. The purpose of this paper is to identify the components responsible for the putrid aroma of the ripe fruits and to determine their approximate level.
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Experimental Sample Preparation Ginkgo fruits (Ginkgo biloba) were obtained from the Bronx Botanical Gardens, N.Y.C. The fruits were of varying degrees of maturity and were separated into four arbitrary maturity stages. Four grams of ginkgo flesh were homogenized with 20g of deionized water. The homogenate was indirectly steam distilled and 8 mL aqueous condensate collected. One gram of sodium chloride was added and the system was extracted with 0.8g diethyl ether (containing 1 μ ι ethyl nonanoate per lOmL diethyl ether) using a Mixxor (Altech, Deerfield, IL) as described by Parliment (3). Analysis The samples were analyzed on a Perkin Elmer Model 3920 gas chromatograph which was equipped with a DB225 (25% cyanopropyl/25% phenyl/50% methyl silicon) column measuring 30m χ 0.53mm i.d. χ 1 μ thickness. The column was held 4 minutes at 80°C and then programmed to 200°C at 8°C/min. Samples were analyzed in duplicate and data collection and reduction performed on a Perkin Elmer Nelson Model 2600 Data System. Component identification was confirmed by GC/MS using a Varian Model 3700 interfaced to a Finnigan Ion Trap Mass spectrometer. The sample was separated on a DB5 (phenyl methyl silicon) column measuring 15m χ 0.32mm i.d. χ 1μ thickness. Spectra of the separated components were compared to spectra generated from pure reference materials.
Results and Discussion The distillates from the ripe fruits possessed a strong cheesy rancid aroma, as did the ethereal extracts. The extracts were analyzed by GC/MS techniques. A unique aspect of the ginkgo fruit is the fact that it contains essentially only two volatile compounds, butanoic and hexanoic acids. These two components are respectively described by Arctander (4) as ''reminiscent of rancid butter" and "fatty-rancid...sweat-like". The levels of these components at various stages of ripeness are presented in Table I. Also presented in the Table are the reported threshold values of these two compounds. It is apparent that the unripe fruits do not have measurable butanoic or hexanoic acids and at this stage of maturity we observed them to be without appreciable odor. Upon ripening the fatty acid levels increase dramatically, reaching a combined level of 500 ppm in the ripe orange stage. The levels are significantly above the threshold values of each components, which explains why these fruits have a reputation for a putrid aroma. The ginkgo nut is roasted and consumed in a number of cultures. We analyzed the nut for presence of the lower fatty acids and were unable to detect any of these compounds. Previous workers (5) have analyzed the fatty acid composition of ginkgo
Rouseff and Leahy; Fruit Flavors ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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278
FRUIT FLAVORS
Figure 1.
Ginkgo Leaf (left) Kernel (center) and Fruits (right)
Rouseff and Leahy; Fruit Flavors ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
25.
PARLIMENT
Putrid Aroma Compounds of Ginkgo biloba Fruits
279
nuts and found them to contain 5.1% total lipid and identified the typical C14:0 to C22:l fatty acids. No acids lower than C14 were detected. Table I.
Free Fatty Acid Levels in Ginkgo Biloba Fruits
MATURITY LEVEL
mg/Kg FLESH n-Butanoic Acid
n-Hexanoic Acid
0
0
Green/Orange
240
90
Yellow/Firm
300
250
Yellow/Overripe
300
200
0
0
0.1-1.0
1.0-10.0
0.004-0.02
0.07-0.1
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Green
Kernels
Thresholds(6) Water(mg/Kg) 3
Air(mg/m )
Acknowledgement The author wishes to acknowledge Dr. Richard McArdle for technical discussions and Mrs. Sara McGarty for samples of ginkgo fruits. Both are with General Foods U S A Research Center, Tarrytown. Literature Cited 1. 2. 3. 4. 5. 6.
Kleijnen, J.; Knipschild, P. Lancet 1992, 340, 1136. Elias, T. The Complete Trees of North America. 1980. Van Nostrand, N.Y., pp 30-32. Parliment, T.H. Perfum Flavorist 1986, 11, 1. Arctander, S. Perfume and Flavor Chemicals. 1969. S. Arctander, Montclair, N.J. Kameyama, H.; Urakami, C. J. Am. Oil Chem. Soc. 1979, 50 549. Van Gemert, L.; Nettenbreijer, A. Compilation of Odor Threshold Values in Air and Water. 1977. TNO, Zeist, Netherlands.
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1994
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