## 4 Discussion
Choline is required in cell membranes, neurotransmitter systems, and metabolic cycles, while GABA is an amino acid that has been garnering attention for its ability to inhibit stress and elevated blood pressure [26; 27]. The \({}^{1}\)H-NMR technique for measuring taste- and nutrient-related metabolites is a relatively new approach in food analysis [17; 18]. The relative concentration of these taste-related substances from the \({}^{1}\)H-NMR analysis corresponded the TSS and TA data (Figure 2f,g), suggesting the effectiveness of the method in evaluating the taste and nutrient qualities of citrus fruits. Shiikuwasha and calamansi juices had different VOC profiles, with whole fruit juices characterized by greater volatile concentrations and more complex profiles than juices made from the edible parts only (flesh juices) (Figure 3). The aroma qualities of shikuwasha and calamansi could thus be distinguished even when the juice was derived from the edible parts or when consumed as raw fruits. However, the inclusion of fruit peels, a source of essential oils [14; 28; 29], in the production of whole juice facilitated the distinction between the two cultivars. The VOCs in both cultivars are mainly composed of monoterenes and sesquiterpenes (Supplementary Table S1, Supplementary Figure S3), and their overall compositions are consistent with those reported previously [7; 8; 14; 16]. Consistently, high amounts of limonene (citrus-fruity odor), \(\gamma\)-terpinene (woody-oily), and \(p\)-cymene (green) are found in the three shikuwasha cultivation lines, while limonene is the sole predominant volatile in calamansi [28; 29; 30]. \"Izumi kugani\" and \"Ogimi kugani\" could be distinguished based on volatile content only when examining the prepared whole juice (Supplementary Figure S3), suggesting the importance of peel parts in constructing the aroma quality of each fruit juice. In addition, \"Izumi kugani-like\" can feature woody-green and citrus-floral aromas from thymol and (\(E\))-\(\beta\)-farnesene, respectively [28]. On the other hand,calamansi, which contains greater amounts of sesquiterpenes, esters, and aldehydes, may have additional fruity and grassy aromas [28; 29; 30]. The combined PCA plots allowed the visualization of the effects of taste- and aroma-responsible compounds in shiikuwasha and calamansi (Figure 4). The balance between sugars and organic acids in citrus is important, and strong or moderate sweetness along with typical fruity or fresh citrus odors are generally preferred [9]. The two cultivars had different flavor characteristics, with shiikuwasha containing higher sucrose levels and calamansi being rich in organic acids; the mixed fruit juice of the two cultivars can thus incorporate the best features of both. Moreover, the whole juices of all three shiikuwasha lines and calamansi were clearly separated in the PCA plots, suggesting the importance of the organic substances in the peel parts for distinguishing the overall aroma quality [29; 30]. In addition to having a richer aroma, the juice from whole fruits can be perceived as more bitter and asringent than that of flesh juice because it may include limonoids and flavonoids from the peels [14; 25]. Accordingly, the peeling process greatly affects the composition of taste and aroma compounds in shiikuwasha and calamansi juices, thereby altering their flavor characteristics.