Furanones in Strawberries: Evolution during Ripening and Postharvest Shelf Life Ana G. Pe ´rez, Raquel Olı ´as, Carlos Sanz, and Jose ´ M. Olı ´as* Departamento de Fisiologı ´a y Tecnologı ´a de Productos Vegetales, Instituto de la Grasa, CSIC, Avenida Padre Garcı ´a Tejero 4, 41012 Sevilla, Spain Furaneol, mesifurane, and furaneol glucoside contents during ripening of four strawberry varieties (Oso Grande, Chandler, Tudla, and I-101) have been analyzed. Patterns of furanone contents were similar for the four varieties, amounts increasing during ripening to reach the highest values at the overripe stage. However, furaneol and derivatives differed quantitatively among varieties. The amount of furaneol shown by Oso Grande at the overripe stage is the highest so far reported (37.05 μg/g fw). The highest content in mesifurane and furaneol glucoside was found in the I-101 variety, at the overripe stage, 23.5 and 13.2 μg/g fw, respectively. Results obtained in eight different varieties, at commercial maturity stage, also showed quantitative differences. Strawberries were stored at 1 °C for 2 days to simulate refrigerated transport and then kept for 7 days at 17 °C to simulate the shelf life period. At 17 °C, the amount of mesifurane and furaneol glucoside increased more than 50% with concomitant loss of furaneol. Keywords: Strawberry; flavor; furanones INTRODUCTION Aroma development is one of the most prominent changes that occurs during ripening of fruit. The aroma is also an important quality factor that influences consumer acceptability of fruits. Strawberry aroma is mainly determined by a complex mixture of esters, alcohols, aldehydes, and sulfur compounds (Schreier, 1980; Dirinck et al., 1981). Although no character impact compound has been found for strawberry aroma, some researchers consider 2,5-dimethyl-4-hydroxy-3(2H)- furanone (furaneol) and 2,5-dimethyl-4-methoxy-3(2H)- furanone (mesifurane) as two of the most important aroma contributors (Pyysalo et al., 1979; Larsen and Poll, 1990, 1992). Both furaneol and mesifurane have strong, sweet, and pleasant odors. Furaneol imparts caramel burnt sugar notes at high concentrations and becomes fruity at lower concentrations (Re et al., 1973). Mesifurane is described as having a more sherry-like aroma (Hunter et al., 1974). Recently Larsen and Poll (1992) found that a mixture of furaneol and ethyl butanoate presented a strawberry-like odor. Several studies have identified the presence of fura- neol, mesifurane (Hirvi and Honkanen, 1982; Douillard and Guichard, 1990), and furaneol glucoside (Mayerl et al., 1989) in strawberries, but these compounds have not been found in all cultivars. Factors such as furaneol water-soluble nature (Pyysalo et al., 1979; Douillard and Guichard, 1989) and thermal instability (Flath and Forry, 1970; Shu et al., 1985) could well account for the failure of some authors to detect these compounds. The new analysis procedure described by Sanz et al. (1994) involves HPLC separation and quantitation of furaneol and its derivatives which avoids some of the risks of thermal oxidative decomposition inherent in GC analysis. In this work, changes in furanone contents during strawberry ripening and postharvest shelf life have been studied using this method. EXPERIMENTAL PROCEDURES Materials. Plants from Oso Grande, Chandler, Tudla, and I-101 strawberry varieties were greenhouse grown in optimum conditions of light, soil, and diseases control. Strawberry flowers were marked the day of blooming, and fruits were harvested at four visual ripening stages: white, pink, red, and dark-red (overripe). Strawberry fruits from Camarosa, Car- tuno, Cartcua, Carlsbad, Laguna, Sunset, Seascape, and Cuesta varieties were grown in field at Cartayfres (Cartaya, Huelva) and sampled at commercial maturity stage (more than 75% red color). Oso Grande fruits used for the shelf life study were also harvested at commercial maturity stage in Torreagro (San Bartolome de las Torres, Huelva). Fruits were placed in 0.5 kg poly(ethylene) terphthalate baskets mechanically filmed with poly(propylene) (Poligal, thickness 25 μm), by means of a flow-pack device. The poly(propylene) film had an O 2 transmission rate of 750 cm 3 /m 2 /24 h at 23 °C and a moisture vapor trasmission rate of 1.1 g/m 2 /24 h at 23 °C and 85% RH. Fruits were immediately stored at 1 °C for 2 days to simulate refrigerated transport and then stored for 7 days at 17 °C to simulate the shelf life period. Control fruits were stored at 1 °C. Preparation of Sample for HPLC. Strawberries were cut symmetrically in four pieces. Four portions from four different fruits (ca. 20 g) were randomly sampled and ground with 5 mL of distilled water in a Waring blender at 0-4 °C. Celite 545 (10 g) was added and after mixing allowed to settle for 5 min. The mixture was filtered, washed three times with 10 mL of distilled water, and again filtered first through a 0.45 μm and then through a 0.2 μm nylon membrane before HPLC analysis. HPLC Analysis. Quantitative HPLC analysis was carried out according to the method described by Sanz et al. (1994) with slight modifications. A liquid chromatograph, Beckman Golden System, equipped with an ODS (4.6 mm × 250 mm) 5 μm column was used. UV detector was selected at 280 nm, and the injection volume was 20 μL. The mobile phase utilized for the separation of furanones consisted of two eluents: 0.2 M sodium acetate/acetic acid, pH 4 (solvent A), and methanol (solvent B). Chromatographic conditions were 0-11 min, isocratic 13% B; 11-26 min, gradient 13-23% B; 26-30 min, isocratic 23% B; and 30-33 min, gradient 23-80% B (cleaning process). * Author to whom correspondence should be ad- dressed. 3620 J. Agric. Food Chem. 1996, 44, 3620-3624 S0021-8561(96)00099-4 CCC: $12.00 © 1996 American Chemical Society