Pandan wangi 455
as temperature, pH, and heating time have considerable effects on the overall aroma
of the processed Pandanus leaves.
27.3 Chemical structure..........................................................................
Chemical constituents of P. maryllifolius Roxb. have been studied in both volatile
and higher molecular weight fractions. Early studies reported a number of volatile
compounds in groups of alcohols, aromatics, carboxylic acids, ketones, aldehydes,
esters, hydrocarbons, furans, furanones and terpenoids. Some of these volatiles were
suggested to play a role in aroma of P. amaryllifolius leaves, obtained in both fresh
and dried forms. Their chemical structures were identified utilizing mainly a combined
gas chromatographic and mass spectrometric technique (Teng et al., 1979, Jiang,
1999, Wijaya and Hanny, 2003). It was not until the report of Buttery in 1982 that the
compound mostly contributed to the flavor of pandanus leaves has been well known,
namely, 2-acetyl-1-pyrroline ( 1 ) (Fig. 27.1). This five-membered N-heterocyclic ring
compound was identified for the first time as the important aroma component of
cooked rice (Buttery et al., 1982) and freeze-dried leaves of P. amaryllifolius Roxb.
(Buttery et al., 1983).
The very low odor threshold value, 0.1 nL/L of water (Buttery et al., 1988), has
made this volatile the key impact aroma compound frequently found in processed
and cooked foods. Its formation in foods has been suggested by many researchers to
occur during food processing at elevated temperature through a reaction called ‘Maillard’
(Weenen, 1998). So far, 2-acetyl-1-pyrroline has been found to occur naturally only
in P. amaryllifolius Roxb., Vallaris glabra Ktze. (bread flower) (Wongpornchai et al.,
2003), and some aromatic rice varieties such as Basmati rice of India, Khao Dawk
Mali 105 of Thailand and Kaorimai of Japan (Buttery et al., 1986, Laksanalamai and
Ilangantileke, 1993, Tava and Bocchi, 1999). In P. amaryllifolius, the compound was
found not only in plant leaves but also in stem and root (Gangopadhyay et al., 2004).
However, its concentrations in fresh plant parts are varied depending on age and
growth stage of the plant as well as climate and location of planting. Fresh pandanus
leaves are found to contain higher amounts of 2-acetyl-1-pyrroline than those at dried
stage, though they hardly smell. The reason lies in the partial distribution of the
aroma compound inside and outside the leaves.
A polar moiety of 2-acetyl-1-pyrroline has made the compound more readily
dissolve in the fresh leaf tissue where the percentage of water is relatively high.
When the leaves are withering and the water content is reduced, the compound is
then forced to partition into the gas phase, resulting in the pleasant smell continually
released from the withering leaves. Therefore, the extraction of the aroma fraction
from P. amaryllifolius is more efficient when fresh leaves are used. Solvent extraction
at room or lower temperature employing a non-toxic solvent or carbon dioxide, so
called supercritical fluid extraction, has been the method of choice and gained higher
popularity among food research institutions and industries (Laohakunjit and Noomhorm,
2004; Bhattacharjee et al., 2005). Apart from 2-acetyl-1-pyrroline, some other odorants
reported include ethyl formate, 3-hexanol, 4-methylpentanol, 3-hexanone and 2-
hexanone, trans-2-heptenal, b-damascenone, 4-ethylguaiacol and 3-methyl-2-(5H)-
furanone. This furanone has often been found as a major component.
In the polar fractions of P. amaryllifolius leaf extracts, a number of alkaloids
were identified starting with a piperidine-type alkaloid, (±)-pandamarine ( 2 ). This