*3.1.2.3 Carotenoids*

Carotenoid content decreases throughout ripening, with a higher content in the grapes exposed to the shade than those exposed to the sun. In grapes grown in high altitude, the content is also lower, due to the low temperatures and higher humidity [60–62]. Its content in grapes ranges between 15 and 2.000 μg/kg. Lutein and β-carotene stand out as the most abundant, as well as neoxanthin, flavoxanthin and others in smaller quantities [63].

Carotenoids are not found in grape juices and in wines made without maceration, as they are degraded during the breaking of the grape and the vinification. Light and oxidases are capable of degrading carotenoids into smaller fragments, more soluble and more fragrant. Among the compounds that are formed in the decomposition of carotenoids, norisoprenoids are worth mentioning because they have low perception thresholds that make them play an important role in the aroma of wine. This degradation can be direct or with an intermediate step that is the formation of glycoconjugates, which can then release their volatile aglycone during fermentation through enzymatic and acid hydrolysis processes [64, 65].

#### *3.1.2.4 Glycosylated precursors*

All grape varieties have the same glycosylated derivatives, being Moscatel varieties the most concentrated. They appear in greater content in the skin than in the pulp or juice. These compounds are four types of glycosides: one monoglycoside (β-D-glucopyranoside) and three diglucosides

(*O*-α-L arabinofuranosyl-β-D-glucopyranoside, 6-*O*-α-L rhamnosyl-β-Dglucopyranoside and 6-*O*-β-D apiosyl-β-D-glucopyranoside) [66].

Although grapes contain enzymes (β-glycosidases) capable of releasing some of these compounds during winemaking, under normal winemaking conditions, glycosylated precursors have a poor effect on the development of the aroma since its optimal activity is developed in other pH values [67].

volatile constituents formed during fermentation (**Table 3**) will quantitatively represent most of the aroma constituents [72]. Malolactic fermentation is not interesting in all situations. For example, in white wines it is interesting to avoid it since this type of fermentation leads to a loss of freshness and varietal aromas, which are

*Management of Wine Aroma Compounds: Principal Basis and Future Perspectives*

Main alcohols synthesized in alcoholic fermentation are 2- and 3-methylbutanol, 1-propanol, 2-methylpropanol, 1-butanol, 1-pentanol, 2-phenylethanol, 3-methylthio-propanol, tyrosol and tryptophol, being its average total content between 400 and 500 mg/L. These compounds are produced at the metabolism of amino acids, so their concentration depends on the nitrogen content of the grape juice, the yeast species and the factors that influence their development [73].

Together with alcohols, these compounds are the main markers of the fermentative aroma. Fatty acids are formed as a result of the interruption of the process of elongation of acetyl-CoA by hydrolysis. Regarding esters, most of them are formed enzymatically, by the initial activation of fatty acids combined with coenzyme A (CoA) [74]. These compounds are usually found in low concentrations, but above the threshold of perception. They are also pleasant aromas (fruit mainly) except

These compounds arise from the metabolism of yeasts by decarboxylation of the α-ketone acids formed in the biosynthesis of higher alcohols. They remain in the wine in small quantities, due to the strong reducing activity of yeast during fermentation. Sulfur dioxide and alcohols react to the pH of the wine with the

These are compounds that generally provide intense and unpleasant odors. Within this group are thiols, sulfides and thioesters. They can be classified

according to their weight in compounds of low molecular weight (sulfur functional group predominantly on odor) or high molecular weight (complex participation in

The most abundant nitrogen compounds are acetamides from primary amines and their corresponding amines. Acetamides have a smell similar to uric acid. They

They are compounds related to hydroxy acids because they are obtained by intramolecular esterification of these compounds: 4-hydroxy acids lead to γ-lactones and 5-hydroxy acids to δ-lactones; both are oxygenated heterocycles [69].

carbonylated compounds, forming sulphydric combinations [69].

aroma due to its analogy with higher alcohols) [69].

are produced by *Bacterium manitopeum* [76].

desirable characteristics in this type of wine.

*DOI: http://dx.doi.org/10.5772/intechopen.92973*

*3.2.2.1 Alcohols*

*3.2.2.2 Fatty acids and esters*

ethyl acetate (over 100 mg/L) [75].

*3.2.2.3 Carbonylated compounds*

*3.2.2.4 Sulfur compounds*

*3.2.2.5 Nitrogen compounds*

*3.2.2.6 Lactones*

**59**
