**1. Introduction**

Strawberries are valued for their harmonious taste and attractive, pronounced aroma, which is formed under the effect of volatiles. Strawberry aroma is known to be very specific and more than 360 compounds constitute its components, such as esters, aldehydes, ketones, alcohols, lactones, terpenic compounds, furanone [1–4]. Esters are considered to be the major components (over 130 different esters were identified); according to various data, they constitute 25–90% of the total amount of volatiles of ripe strawberries and add some flower or fruit flavors to strawberries [1, 2]. About 49 components were identified in volatile compound composition in strawberry varieties "Polka", "Ducat" and "Honey": esters, aldehydes, ketones, furanone, organic acids, aroma compounds, lactones, terpenic compounds, and alkanes. The most meaningful ones are: esters**—**12.8–41.8%, aldehydes**—**5.9–15.9%, ketones—8.7–35.6%, furanone—22.7–24.4% and organic acids—2.47–21.85% [5].

Aldehydes and furanone represent a large amount of volatile compounds of strawberries, their share being 50%. The latter adds a grass, sweet, or caramel flavor to the strawberry aroma [6–8]. Instead, according to other data, furanone is the main source of the strawberry aroma. Their level in the most aromatic cultivars exceeds a corresponding indicator of other cultivars by 20 times [4]. A small amount of aroma volatiles can be referred to as terpenic and sulfur compounds which can also have a considerable impact on strawberry aroma [9]. The most important chemical compounds which form strawberry aroma methyl butanoat, ethylbutanoate, 2-methylbutanoat, ethyl hexanoat, methylhexanoat, methyl 2-methylpropanoat [10], 4-hydroxy-2,5-dimethyl-3(2H)-furanone and 4-methoxy-2,5-dimethyl-3(2H) furanone [6, 11, 12], (Z)-3-hexenal; butan-2,3-dion and linalool [13].

The most common ethers are: ethyl butanoate, butylacetate, ethylcrotonate, ethylcapronate, ethyl 3-hydroxycapronate, which give them fresh grass tone. Among aldehydes, those will be trans-2-hexenal and pentanal. Palmitic acid, carvone, and acetoin were found in all studied strawberry cultivars. Terpenic compounds are represented by nerolidol and linalool which give spicy notes to a strawberry flavor [14, 15]. Tetradecane was defined in the alkane class. Furanone were represented by 2,4-dioxy-2,5-dimethyl-3(2H)-furan-3-one, 2,5-dimethyl-4-methoxy-3(2H)-furanone (mesifurane) and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (furaneol) [5].

Genetic peculiar features of a cultivar, a maturity degree, and storage conditions have an effect on the composition and concentration of volatiles [9]. The aroma of strawberries can change during storage [3, 16] and processing them into canned products [17]. For instance, the availability of methyl ester is a characteristic feature for "Hokowase", "Kent", "SengaGigana" and "Annapolis" strawberries, the share of which is equal to 70% of the total content of volatiles, whereas the availability of ethyl3-methylbutonoat and 3-methylacetate is more typical for cultivars "Kent" and "Micmac", and that of hexylacetate—for "Honeoye". Linalool was found in "SengaSengana" and "Annelie" strawberries [1].

Ethylbutanoate (10.1–30.65%), trans-2-hexenal (5.31–15.55%), acetoin (8.20–35.67), 2,5-dimethyl-4-methoxy-3(2H)-furanone (mesifurane) (19.08–19.92%) and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (3.43–4.40%) were typical compounds for the flavor of the strawberry varieties studied. In addition, strawberries of Honey variety showed high content of Hexanoic (caproic) acid (9.54%) and Hexadecanoic acid (5.08%) [5].

The aroma of strawberries is formed in the process of ripening under the effect of enzymes. It is a known fact that when the strawberry color changes from white to a total red one the content of volatiles in them increases by 14 times. In green, unripe strawberries aldehydes and alcohols predominate and they add grass, green aroma, and in ripe strawberries—esters and furanone [10]. According to [18], EA and aldehydes predominate in green strawberries, in white berries—ketones and alkanes, and in red strawberries—esters, acids, furanes, and alcohols [18]. I has been experimentally proved that in the process of ripening the concentration of grass aroma components, such as hexanal, trans-2-hexanol and cys-3-hexenylacetat, decreases gradually [19]. Instead, the total ether content, including esters, increases, the content of furanone and lactones grows rapidly, the former were not found in green strawberries. Besides, during ripening the concentration of general aldehydes, aromatic compounds and alcohols undergo change [4].

Aldehydes and esters result from the enzymatic oxidation of lipids and a fermentative bio-synthesis of alcohols and acids, the latter occurs with the participation of alcohol-dehydrahenaza [3]. Alcoholacetyltransferaza plays a decisive role in a taste

*Volatile Components of Strawberries DOI: http://dx.doi.org/10.5772/intechopen.104213*

bio-synthesis during strawberry ripening through the formation of esters which are the main components of strawberry volatiles [20], this takes place together with volatile free fatty acids in mesocarp cells and strawberry protoplasts [21]. The role of Fragaria 3 ananassaxinon-oxydoreductasa in bio-synthesis of 2,5-dimethyl-4-hydroxy-3(2H)-furanone has been proved [22], and the formation of 2,5-dimethyl-4-hydroxy-3 (2H)-furan-3-one catalyzes β-glucozidaza [23, 24].

The environmental conditions, in particular lighting, are the major factor in the formation of a strawberry aroma. It has been proved that shading by 47% leads to a considerable decrease in the concentration of hexanal, hexanal, ethyl-methyl butyrate, and methylbutyrat in strawberries, as compared with well-lighted plants [21], which is due to the deceleration of a photosynthesis process in the plants, and, as a result, the decrease of the number of primary metabolism products; the latter are the raw materials for the synthesis of volatiles [25, 26].
