**6. Volatile compounds**

Volatile compounds influence the sensory quality of fruits. Their aromas are formed from a complex group of chemical substances such as aldehydes, alcohols, ketones, terpenes and esters, among others. These compounds usually show a low concentration in fruits and their variability depends on cultivar, climatological conditions, maturity and storage conditions, among other factors [30]. In prickly pear fruit pulp, the content of these compounds varies from 3.33 mg 100 g<sup>−</sup><sup>1</sup> to 14.86 mg 100 g<sup>−</sup><sup>1</sup> [31].

Even though prickly pears have no strong aroma, up to 61 compounds have been identified [32]. In a recent research [31], the studied cultivars showed aldehydes and terpenes as the most numerous compounds. Both chemical groups and alcohols were the most abundant compounds. However, other studies reported alcohols [32–34] and esters [35] as the most numerous and abundant compounds. Some predominant compounds are D-limonene (citrus notes), 2,6-nonadienal (vegetable notes), nonanol (green, melon and fatty attributes), 2-hexenal (almond, apple green, sweet and vegetable notes), and 1-hexanol (green and sweet notes), among others [31–33].

Although prickly pear fruits are highly valued for their health-promoting benefits, sensory analysis is needed to complete the knowledge of aroma of this fruit and the effect of the cultivar [31].
