# Differentiation of Fresh and Processed Fruit Juices Using Volatile Composition
## 3 Discussion  
In sum, fruit aroma is an important indicator, which may reflect the quality of future fruit juice. The contribution of each VOC to the specific aroma signature of each fruit species/types depends on the activity and substrate specificity of the relevant enzymes in the biosynthetic pathway, the substrate availability, the OT above which VOC can be detected by smell, and the presence of the other VOCs [5]. The esters represented more than 45.15% of the total volatile profile of apple, pear, and red fruit juices, which is in accordance with previous studies that report esters as the most abundant chemical group in pear and apple fruit juices [6; 7; 11; 13]. Regarding this chemical group, hexyl acetate, a dominant esters in pear juice, has been reported as possessing a strong pear-like odor [12]. Moreover, ethyl octanoate contributes to sweet and fruit odors in pears, while hexanal, ethyl acetate, hexyl acetate, ethyl butanoate, and butanol are identified as impact volatiles in Conference pears [13]. On the other hand, terpenids, one of the most dominant chemical groups of VOCs found in orange and grape fruit juices, have shown beneficial functions as well as nutraceutical activities. Recently, some studies in the field of cancer research and food nutrition sciences have been performed on these VOCs due to their potential anticancer properties [44]. Among them, limonene (a dominant VOC in orange juice) has been reported to be a bioactive food component from citrus fruits, with a potential role in breast cancer prevention and treatment [45]. In addition, limonene reduces the oxidative stress in Streptozotocin-induced diabetic rats by decreasing lipid peroxidation and sparing the activities of antioxidant enzymes [46]. Linalool (a dominant VOC in red fruit juice) and terpineol (a dominant in grape fruit juice) are responsible for the fruity and floral notes of food matrices. Moreover, linalool and its degradation product, \(\alpha\)-terpineol, have been reported as potent antimicrobial agents against periodontal and cariogenic bacteria [47]. Anti-inflammatory effects were also associated with these terpen [48]. \(\alpha\)-Farnesene, a specific terpenoid, with green and herbaceous aroma descriptors, has been reported as the most abundant terpene in fresh apple juice [49], which is in agreement with the results of our study, since we detected GC peak areas (\(\times 10^{6}\)) in fresh and processed apple juices of 419.32 and 8.16, respectively. Moreover, according to previous studies, the aroma of squeezed orange juice is primarily associated to esters (e.g., ethyl butanoate, ethyl 2-methylpropanoate), aldehydes (e.g., acetaldehyde, hexanal, octanal), in addition to a smaller number of terpenids (e.g., myrcene, \(\alpha\)-pinene, potentially limonene, linalool, geranal). All these VOCs are responsible for the citrus, green, sweet fruit, and floral notes from fresh orange juice [50; 51; 52]. There are differences between the VOCs contained in fresh and processed fruit juices, with processed juices having the highest levels of VOCs. Indeed, a recent study of fresh and commercial pomeranate juice indicated that there were marked differences between endogenous VOCs extracted in the laboratory versus what was often found in commercial products [53]. This fact may be due to several characteristics of fruits (e.g., geographical and botanical origin, varieties, ripening stage, farming practices, and post-harvest handling), the process applied in juice extraction and its production (e.g., enzymes, heat, and filtration), as well as storage conditions [5]. A recent assay reported that the volatile loss generally continued through pasteurized storage, and the lowest volatile levels were recovered after one, two, and four months of storage [54]. Another study highlighted that changes in volatile chemicals could provide useful information about juice processing for the selection of the optimal harvest time and for setting a precise blending strategy [55].