## 4 Discussion
For instance, there are caramel-like odors from 4-methoxy-2,5-dimethyl-3(2H)-furanone; sweet-pineapple and caramel-like odors from 4-hydroxy-2,5-dimethyl-3(2H)-furanone; fruity and coconut-like odors from \(\gamma\)-octalactone; and coconut-like odors from \(\delta\)-octalactone. These volatile organic substances, which were found in moderate amounts in Okinawan pineapple, might be derived from various biosynthesis pathways that occur during fruit maturation. For instance, alcohols are synthesized from fatty acids through the lipoxygenase oxidation pathway and from degraded amino acids [32]. On the other hand, the biosynthesis of terpenes is mainly regulated by terpene synthases from universal five-carbon precursors, i.e., isopentenyl diphosphate and dimethylallyl diphosphate [32; 33]. Additionally, furanones might be synthesized from the D-fructose-1,6-diphosphate precursor, while lactones are fatty acid-derived molecules [32; 34]. Nevertheless, variation in the content and composition of free volatiles revealed the aroma distinctiveness of each cultivar, and thus, the flavor quality of Okinawan pineapple. Glycosidically bound volatile substances are produced in horticultural plants through various biochemical reactions in the presence of enzymatic catalysts such as UDP-glycostransferases that mediate the glycosylation of aglycone acceptors to activated nucleotide sugars [10; 12; 16]. The releasing of these aglycone volatiles from glycoside extracts revealed that Okinawan pineapples of different cultivars have potent aroma resources which are stored in their fruit tissues. The total content of liberated compounds via enzymatic hydrolysis tended to be associated with total free volatile components in which 'Yonekura' had greater concentrations of these two aroma compound forms, whilst 'N67-10' and 'Yugafu' contained comparable total amounts (Figures 1B and 2). This trend indicates that both the free and glycosylated substances of a pineapple cultivar are produced from equivalent levels of aroma precursors, and their amounts and compositions can be used for differentiating individual pineapple cultivars [11]. The main volatile compounds which were liberated at concentrations of more than 1 \(\mu\)g/100 mL, such as chavicol and eugenol, have strong distinct aromas. These phenylpropenes could emit medicinal-herbal odors such as spicy-floral and spicy-clove scents, respectively [27; 35]. Moreover, released geraniol might provide potent sweet-floral, fruity, and citrus aromas [30; 31] Additionally, the released minor components from pineapple glycosides have been known to be responsible for producing various characteristic odors, such as rose-honey (phenylethyl alcohol), sweet-floral (benzyl alcohol), rose-green (2-ethyl-1-hexanol), and floral-oily-green (1-hexanol) [27; 28; 29]. Among these glycosylated volatile molecules, 2-ethyl-1-hexanol and 1-hexanol were also found in their free forms (Table 2; Figure 2B), indicating that complex biochemical reactions had occurred during fruit maturation; thus, more studies are needed to reveal the molecular mechanisms underlying aroma development in pineapple [12]. Higher concentrations of two glycosides of phenylpropenes, chavicol-O-\(\beta\)-D-glucopyranoside and eugenol-O-\(\beta\)-D-glucopyranoside, were detected in 'Yonekura', whilst comparable amounts of these non-volatile substances were found in the other cultivars (Figure 3). This trend is also in agreement with the above descriptions on the total content of both free- and released-volatile components (Figures 1B and 2). However, the amount of eugenol-O-\(\beta\)-D-glucopyranoside in 'Yonekura' in particular was much higher than that of its released volatile compounds after hydrolysis. Nevertheless, these glycosidically bound volatile components are important potential sources of aroma compounds as strong volatiles in Okinawan pineapple for storing chavicol and eugenol with strong characteristic medicinal-herbal aromas [27; 35].