Scientia Horticulturae 150 (2013) 47–53 Contents lists available at SciVerse ScienceDirect Scientia Horticulturae journa l homepage: www.elsevier.com/locate/scihorti × Differences in volatile ester composition between Fragaria ananassa and F. ଝ vesca and implications for strawberry aroma patterns a,b b c b a,∗ Jing Dong , Yuntao Zhang , Xiaowei Tang , Wanmei Jin , Zhenhai Han a Institute for Horticultural Plants, College of Agronomy and Biotechnology, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian District, Beijing 100193, PR China b Institute of Forestry and Pomology, Beijing Academy of Agriculture and Forestry Sciences, No. 12 Ruiwangfen, Xiangshan, Haidian District, Beijing 100093, PR China c Beijing Vegetable Research Center, Beijing Academy of Agriculture and Forestry Sciences, Banjin, Haidian District, Beijing 100097, PR China a r t i c l e i n f o a b s t r a c t Article history: Esters are a very important component of strawberry (Fragaria sp.) aroma. In this study, fruit volatiles Received 8 April 2012 were isolated by solid-phase microextraction and analyzed by gas chromatography–mass spectrometry Received in revised form 1 November 2012 (SPME/GC–MS). It was found that F. × ananassa had more esters than F. vesca, but there was no significant Accepted 1 November 2012 difference in average relative content of esters. Twenty five esters were selected as predominant esters, 16 of which were prevalent in F. × ananassa and another 16 in F. vesca. Among them, hexyl acetate, Keywords: octyl acetate, ethyl butyrate, ethyl hexanoate, ethyl octanoate, methyl decanoate, and ethyl decanoate Volatile ester composition were found in both F. × ananassa and F. vesca, while 1-methyltridecyl acetate, myrtenyl acetate, trans- Aroma pattern pinocarvyl acetate, and ethyl dodecanoate were only present in F. vesca. The numbers of carbons of the F. × ananassa predominant esters in F. × ananassa were usually smaller than those of F. vesca. Ethyl hexanoate and octyl F. vesca × acetate were the esters with the highest average concentrations in F. ananassa and F. vesca, respectively. It was found that hexyl acetate, methyl butyrate, hexyl butyrate, methyl hexanoate, and ethyl hexanoate ≥ were major contributors to the aroma of cultivated strawberry because their odor values were 1 in every cultivar, however, no ester was found to be so important like that for all of the F. vesca accessions. Most × of the predominant esters of F. ananassa were described as having only fruity odor. Unlike the case of F. × ananassa, nearly all of the predominant esters of F. vesca have a noticeable floral odor in addition to a fruity note. That may contribute to the variations in fruit aroma. The average number and proportion of acyl and alkyl esters differed between species. Acetate esters predominated in F. vesca, accounting for a × significantly higher average proportion of total esters than in F. ananassa. All the differences in volatile esters are likely to play a key role in the different aroma patterns of F. × ananassa and F. vesca. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Fruit aroma is the result of the presence of various aroma com- pounds. Researchers have been studying the differences in aroma Strawberry (Fragaria sp.) is planted throughout the world. One volatiles between the cultivated strawberry (F. × ananassa) and of the major quality characteristics of strawberry is its aroma. It has wild strawberry species. Staudt et al. (1975) detected 120 volatile been reported that a large number of volatile compounds such as compounds in fruit of F. nilgerrensis and found that it had a different esters, terpenes, alcohols, ketones and furans contribute to straw- aroma composition from that of F. × ananassa, with methyl ben- berry aroma (Pérez et al., 1992; Zabetakis and Holden, 1997). The zoate, benzyl acetate, methyl cinnamate, and ethyl cinnamate being fruit aroma is influenced by genotype and environment (Forney the most prominent in the former. Pyysalo et al. (1979) identified et al., 2000). Wild strawberries tend to have a more intense aroma butyl formate, octyl acetate, decyl acetate, benzyl acetate, carveyl than cultivated ones. Fruit aroma patterns vary among Fragaria sp. acetate, decyl butanoate, methyl nicotinate, methyl anthranilate, (Ulrich et al., 2007). and methyl N-formylanthranilate in wild strawberries, but none in F. × ananassa. Ulrich et al. (1997) reported that the main sensory profiles of F. vesca including aromatic, flowery, sweet, and flavor differed notably from those of cultivated cultivars. ଝ This study was financially supported by the Beijing Science and Technology F. vesca has been extensively investigated because of its intense Nova Project (2008B36), the Beijing Natural Science Foundation (6122013) and the aroma (Hirvi and Honkanen, 1982; Pyysalo et al., 1979; Ulrich et al., Beijing Science and Technology Project (Z111100056811035-2). We thank Shahrokh 2007). Compared with F. × ananassa, F. vesca has a marked floral Khanizadeh for his review for the manuscript. ∗ odor. The esters and terpenes of F. vesca are quite different from Corresponding author. Tel.: +86 10 62732467; fax: +86 10 62736613. × E-mail address: [email protected] (Z. Han). those of F. ananassa (Zabetakis and Holden, 1997). The major 0304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2012.11.001 48 J. Dong et al. / Scientia Horticulturae 150 (2013) 47–53 esters contributing to the aromas of F. vesca and F. × ananassa are Shenzhen, China) into a 15 mL sample vial, and sealed hermeti- also different. Methyl anthranilate is a major aroma compound of F. cally. Volatiles were extracted using solid-phase microextraction vesca, whereas methylbutanoate, ethyl butanoate, ethyl hexanoate, (SPME). An SPME fiber coated with 100 ␮M polydimethylsiloxane and methyl 2-methylbutanoate are among the most important (Supelco Inc., Bellefonte, USA) was inserted into the headspace of ◦ odorants of F. × ananassa (Larsen and Poll, 1992; Schieberle and each sampling vial. The vials were then heated in a 35 C water bath Hofmann, 1997). for 25 min to facilitate the release of volatile compounds from the Esters, the largest group of aroma compounds in strawberry, sample to the headspace. The SPME fiber was removed from the account for approximately 25–90% of the volatiles of this fruit, giv- vial and immediately injected into the gas chromatograph (GC). ing it fruity and flowery odors (Beekwilder et al., 2004; Douillard and Guichard, 1990; Jetti et al., 2007; Pérez et al., 1992, 1997; 2.4. GC–MS analysis Schieberle and Hofmann, 1997). The content of esters is thought to be an important basis for the classification of aroma patterns (Ulrich SPME fibers were desorbed in the injection port of a Shi- et al., 1997, 2007). In the related papers which have been reported, madzu QP2010 gas chromatograph–mass spectrometer (GC–MS) ◦ single aroma components including esters were compared among (Shimadzu Co., Kyoto, Japan) at 250 C for 1 min, in splitless different species or cultivars (Aharoni et al., 2004; Pyysalo et al., mode. A DB-5MS column (J & W Scientific Inc., Folsom, USA) × × ␮ 1979; Zabetakis and Holden, 1997). However, no reports compared (30 m 0.25 mm i.d. 0.25 m film thickness) was used. The car- a certain type of volatile compounds to analyze the differences rier gas was ultra-high purity helium (99.999%). The injection port further. This study focused on esters and their impact on aroma was subjected to a pressure of 51.3 kPa, and the GC oven tem- ◦ patterns for the first time to help researchers understand why perature program consisted of an initial temperature of 40 C for ◦ ◦ −1 strawberry fruits have different types of aroma. 2 min, increasing to 220 C with a rate of 8 C min , and holding ◦ Before this experiment was carried out, a preliminary test had at 220 C for the final 6 min. Mass spectra in the range m/z 30–550 been done. It was resulted that there were little differences in ester were obtained by electron ionization (EI) at 70 eV. The ion source ◦ ◦ composition between Japanese cultivars and European & USA cul- temperature was 200 C, and the interface temperature was 250 C. tivars. It was also concluded that though planting pattern could Identification of the compounds was achieved by comparing influence esters on number, type, proportion, etc., the data of green- their mass spectra with those in the NIST (National Institute of house showed good consistency in continuous years. Standards and Technology) library and the Wiley library. Standard Among modern cultivars, Japanese cultivars of F. × ananassa compounds were analyzed in the same conditions as the samples. usually have a stronger aroma than other cultivars. Considering that Compounds were tentatively identified by searching for matches it is an important trend to breed more aromatic strawberries and in the mass spectral libraries, and then had their identities con- Japanese cultivars and wild species (esp F. vesca) certainly will play firmed by comparing their GC retention times with those of a valuable role in future aroma breeding, we focused on compar- authentic compounds. The identities of most compounds were ing volatile esters between Japanese cultivars and F. vesca strains confirmed. in this study. The volatile ester composition of seven Japanese F. × ananassa cultivars and six accessions of F. vesca, which were 2.5. Data processing selected out of nearly 100 collections on the basis of cluster analy- sis of fruit volatiles in the preliminary test, were compared to seek The total ester content was calculated using the peak areas, and to explain the different aroma patterns of the strawberries in terms expressed as percentage of the total volatiles. The peak areas were of esters. also used to calculate the proportion of each type of ester relative to the total esters. 2. Materials and methods Calibration curves were constructed for the quantitative analy- sis of individual esters.