Characterization and Semiquantitative Analysis of Volatiles in Seedless Watermelon Varieties Using Solid-Phase Microextraction JOHN C. BEAULIEU* AND JEANNE M. LEA Food Processing & Sensory Quality Unit, Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 1100 Robert E. Lee Boulevard, P.O. Box 19687, New Orleans, Louisiana 70179 Seedless triploid watermelons have increased in popularity since the early 1990s, and the demand for seedless fruit is on the rise. Sweetness and sugars are crucial breeding focuses for fruit quality. Volatiles also play an important role; yet, we found no literature for seedless varieties and no reports using solid-phase microextraction (SPME) in watermelon. The objective of this experiment was to identify volatile and semivolatile compounds in five seedless watermelon varieties using carboxen divinylbenzene polydimethylsiloxane solid-phase microextraction (SPME) with gas chromatography- mass spectrometry (GC-MS). Fully ripe watermelon was squeezed through miracloth to produce rapid juice extracts for immediate headspace SPME GC-MS. Aldehydes, alcohols, ketones, and one furan (2-pentyl furan, a lipid oxidation product) were recovered. On the basis of total ion count peak area, the most abundant compounds in five varieties were 3-nonen-1-ol/(E,Z)-2,6-nonadienal (16.5-28.2%), (E)-2-nonenal (10.6-22.5%), and (Z)-6-nonenal (2.0-11.3%). Hexanal was most abundant (37.7%) in one variety (Pure Heart). The most abundant ketone was 6-methyl-5-hepten-2-one (2.7-7.7%). Some sensory attributes reported for these compounds are melon, citrus, cucumber, orange, rose, floral, guava, violet, vegetable, green, grassy, herbaceous, pungent, fatty, sweet, and waxy. Identifying and relating these compounds to sensory attributes will allow for future monitoring of the critical flavor compounds in seedless watermelon after processing and throughout fresh-cut storage. KEYWORDS: Aroma compounds; flavor; gas chromatography; mass spectrometry; melon; solid-phase microextraction; watermelon [Citrullus lanatus (Thunb.)] INTRODUCTION Per capita watermelon [Citrullus lanatus (Thunb.)] consump- tion in the United States has been somewhat stable since 1990 at roughly 14.3 ( 1.1 lbs/year, and seedless watermelon ship- ments constitute three-fourths of the movement of all do- mestically grown watermelons (1). The portion dedicated to fresh cuts has been increasing and now constitutes roughly 25% of the total fresh-cut fruit market (2). Consumers desire seedless watermelons, especially when conveniently packaged as fresh cuts. As a result, new “firmer” seedless varieties have recently been developed and are becoming available. Seed companies breed such releases for sugar content, size, flesh firmness, appearance, and yield. However, there have been very limited reports regarding volatile flavor compounds in watermelon (see Table 1). In a comprehensive review of volatile compounds in water- melon, 71 compounds were reported (3). Most compounds were aldehydes, alcohols, ketones, and furans. Only roughly 15 compounds typically associated with fruity and fruit flavors, such as esters and acids, were reported. Of those 71 compounds, 52 were reported for the first time, while using gas chroma- tography (GC). This was a significant increase from the previous 26 volatile compounds established in watermelons (4). The last comprehensive review of volatile compounds in watermelons tabulated only 75 compounds (5). Again, the majority were aldehydes and alcohols with 23 alcohols, 21 aldehydes, eight ketones, seven hydrocarbons, one acid, two lactones, 12 furans, and one oxide. The main volatile components reported in watermelon were C 9 aldehydes, alcohols, and their esters (3-8). Nonetheless, we have been unable to procure any reports regarding volatiles in seedless watermelon varieties. Most typical sample preparation for compound isolation involves steps that are time and labor intensive, are prone to volatile loss, and often use solvents that are toxic or potential carcinogens. Furthermore, solvent extractions are generally accomplished at high temperatures or under reduced pressure, conditions that can destroy or alter some volatile flavor compounds and/or produce artifacts. Our long-term objective is to rapidly analyze flavor and aroma compounds in fresh-cut fruits and ultimately correlate chemical analyses with those findings obtained by trained sensory panelists. Therefore, we * To whom correspondence should be addressed. Tel: 504-286-4471. Fax: 504-286-4419. E-mail: beaulieu@srrc.ars.usda.gov. J. Agric. Food Chem. 2006, 54, 7789-7793 7789 10.1021/jf060663l This article not subject to U.S. Copyright. Published 2006 by the American Chemical Society Published on Web 09/12/2006