Thailand has numerous tropical fruit that present an exotic taste and flavor. Such fruit have great economic potential as fresh or processed. Durian (Durio zibethinus L.), mangosteen (Garcinia mangostana L.), rambutan (Nephelium lappaceum L.), longon (Lansium domesticum Corr.), and sapodilla (Manilkara zapota van Royer) are native to Southeast Asia (Thailand/Malaysia/Indonesia) and require a year-round, warm, very humid, and equatorial climate. Durian is a member of the Bombacaceae family. One of the most praised of tropical fruits and certainly the most esteemed fruit in the Guttiferae family, mangosteen is almost universally known. Longon, a somewhat less edible fruit of the Meliaceae family, is also known as langsat, lansa, langseh, langsep, lanzon, lanzone, lansone, or kokosan and by various other names in the dialects of the Old World tropics. They are grown in the east and south of Thailand (Morton, 1987).
Native to Southeast Asia (Malaysia and Indonesia), rambutan belongs in the same family (Sapindaceae) as the subtropical fruits lychee and longan and is relatively unknown in the United States (Lam and Kosiyachinda, 1987; Macleod and Troconis, 1982; Ong et al., 1998). Sapodilla is best known as the source of chicle gum, which is the basis of chewing gum manufacturing.
Various studies on postharvest properties and marketing of these fruit have been reported with a few describing the flavor chemistry of durian, rambutan, and sapodilla (Macleod and Troconis, 1982; Weenen et al., 1996; Wong and Tie, 1995). In three varieties of Indonesian durian, 24 of the 43 peaks contributed to their flavor as analyzed by gas chromatography-mass spectrometry (GC-MS). The strongest durian odorant among sulfur compounds was 3,5-dimethyl-1,2,4-trithiolane and nonsulfurous odorant was ethyl 2-methylbutanoate (Baldry et al., 1972; Boelens et al., 1974; Weenen et al., 1996). Sapodilla produces a relatively small quantity of aroma volatiles (in total ≈5 μg·kg−1 of fruit weight) and benzyl-related compounds comprise over 45% of the volatiles, including alkyl benzoates, methyl benzoate, methyl salicylic, and ethyl benzoate (Macleod and Troconis, 1982). The main contributors to rambutan aroma were β-damascenone, ethyl 2-methylbutarate, 2,6-nonadienal, (E)-2-nonenal, and nonanal (Ong et al., 1998).
The literature on postharvest flavor compounds or the composition of volatiles of tropical fruit longon, mangosteen, durian, rambutan, and sapodilla is limited. Volatiles were monitored by GC-MS, after various extraction methods, as simultaneous steam distillation extraction in sapodilla fruit (Macleod and Troconis, 1982), fraction distillation in durian (Weenen et al., 1996), liquid extraction in rambutan (Ong et al., 1998), hydrodistillation in African pear (Jirovetz et al., 2005), and continuous liquid–liquid extraction in pineapple fruit (Elss et al., 2005). Sample preparation such as extraction and isolation of analysis greatly influences the reliability and accuracy of flavor analysis in fruit. Present sample preparation methods for analyzing volatile compounds are liquid–liquid extraction, widely used to extract the typical aroma components, static headspace sampling, direct injection, and solid phase extraction. Most typical sample preparations for compound isolation involve steps that are time- and labor-intensive, prone to volatile loss, and often use solvents that are toxic or potential carcinogens. Furthermore, solvent extractions are generally accomplished at high temperature or under reduced pressure, which can destroy or alter some volatile flavor compounds or produce artifacts. Solid phase microextraction (SPME) is rapid, less laborious, and relatively inexpensive and does not require solvents, purge and trap, preconcentration, or vigorous extraction and heating, which may alter endogenous compounds (Pawliszyn, 1997; Zhang et al., 1994; Zhang and Pawliszyn, 1993). Also, the absorptive nature of the fibers permits assays at nondestructive temperatures. Flavor and off-flavor aromas have recently been assessed in numerous fruit and juices by SPME (Wang et al., 2004; Beaulieu and Grimm, 2001; Jia et al., 1998; Matich et al., 1996; Song et al., 1998; Steffen and Pawliszyn, 1996). Fruit aroma is the result of a special assortment and mixture of different metabolites. The different proportions of volatile components and the presence or absence of trace components determine aromatic properties of fruit (Ayala-Zavalla et al., 2004). Flavor plays an important role in consumer satisfaction and influences further consumption of fruit (Pelayo et al., 2003). The purpose of this study was to survey the flavor compounds of tropical fruits to obtain information that may be valuable for variety improvement of tropical fruits of Thailand.
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