## 3 Discussion
The low volatile abundance in watermelon rind would be easy to mask in food products where a melon flavor is not desired, meanwhile adding nutritional value such as Arg and Cit. A detailed list of volatile compounds in watermelon rind is reported by our most recent publication [29], which results in half of the identified volatiles commonly presenting in both rind and flesh. The present study's results also revealed that the rind of watermelon possessed some aromas identical to the flesh, though volatiles responsible for most melon-like aromas were generally less abundant in the 100% rind sample compared to the 0% rind sample. The prevalence of nine-carbon volatile compounds in the tested samples observed in this study, including (_E_)-2-nonenal; (_Z_)-3-nonen-1-ol; (_E_,_Z_)-2,6-nonadienal; (_Z_)-6-nonenal; nonanal; and (_Z_,_Z_)-3,6-nonadien-1-ol, have been described to have melon, fresh, sweet, fruity, floral, cucumber, and green related aromas [35; 43]. The finding of flavor compounds in watermelon find that were identical to those in flesh affirmed the potential of rind as a melon flavor enhancer. The use of rind as a flavor enhancer was tested in raw watermelon find-flesh blends by consumers in an earlier study [27]. The volatiles in those blends were identified to uncover the interactions between the chemical and sensorial aspects of rind. Despite the presence of those recognizable volatiles, watermelon find consumption is not as popular as is the flesh, suggesting that there are key differences between their flavor profiles. This difference was reflected in not only the total number of identified volatiles, but also their abundance (peak area). Rind concentration in the samples shared a direct relationship with the abundance of nine-carbon alcohols and nine-carbon aldehydes, but the rind lacked the diverse aldehydes, alcohols, terpenoids, and ketones characterizing the flesh. The heat map further accentuated the volatile profile differences between rind and flesh by coloring the rind mostly blue (negative correlation to most identified volatiles) and separating it from the other samples. In other words, samples with greater amounts of rind retained classic melon flavors, but they were missing additional flavor nuances (fresh, green, fatty, citrus, floral, creamy, etc.) contributed by the unique volatile compounds in the flesh. In addition to the knowledge of shared and distinctive volatiles distributed in watermelon flesh and rind, it would be ideal to know the aroma-contributors in watermelon find-an unexplored topic. Extensive studies have been conducted to investigate aromatic compounds in watermelon flesh (juice) by directly using GC-olfactometry (GC-O) as well as odor activity value (OAV) computation [42; 44; 45]. OAVs are the ratio between the quantified volatile content and the corresponding odor threshold level. The majority of studies name nine-carbon aldehydes and alcohols as aroma contributors. Our current study found aldehydes (low volatility, six-carbon and nine-carbon) and unsaturated nine-carbon alcohols to be the major contributors for watermelon rind aroma, suggesting that watermelon rind smelled fresh, green, grassy, and cucumber-like, with intensity much lower than watermelon flesh. Although the dominant aroma compounds were nine-carbon aldehydes and alcohols, it should be pointed out that watermelon flesh should have a richer aroma profile than the description in the literature. It has been mentioned that the combination of nine-carbon alcohols and aldehydes was found to be insufficient to reconstruct the intricate aroma of watermelon [46]. Watermelon flesh (juice) has been described to have fresh, green, cucumber-like, melon-like, fruity, and floral notes [47]. The fruity and floral notes can most likely be attributed to other volatiles groups (not aldehydes or alcohols). For example, certain terpenoids (\(\beta\)-ionone) and esters (hexyl acetate and \(\gamma\)-nonalactone) might contribute floral, fruity, and sweet notes. However, in watermelon find, these volatiles were lacking.