# Analyzing Volatile Compounds of Young and Mature _Docynia delavyi_ Fruit by HS-SPME-GC-MS and rOAV
## 4 Discussion  
Fruit aroma is an important indicator for plant breeding and influences consumer acceptance. Fruits can produce compounds that give them a characteristic aroma during the growth process; therefore, various types of volatile compounds and their quantities result in different aromas [34]. In the present study, the number of esters and terpen in DM was more than that of DY. Esters are essential contributors to fruit aromas; they have low thresholds and generally produce pleasant odors [35]. Esters are generally synthesized through fatty acid metabolism, with critical precursors including linolenic and linoleic acids [36]; these acids are catalyzed by lipoxygenase (LOX) enzymes to generate 9-hydroperoxide (9-HPO) and 13-hydroperoxide (13-HPO) that form C6 and C9 aldehydes by the action of hydroperoxide lyase (HPL), with alcohol dehydrogenase (ADH) and alcohol acyltransferase (AAT) catalyzing their conversion to the corresponding linear esters [35]. In addition, metabolic pathways involving amino acids, such as alanine, valine, and aspartic acid, in fruit also participate in the ester synthesis [10]. Amino transferase (ATF) catalyzes the conversions of amino acids into \(\alpha\)-ketoads, which undergo decarboxylation, reduction, and esterification reactions to generate the corresponding aldehydes, esters, and other volatile compounds. Furthermore, \(\alpha\)-ketoacid acids can combine with coenzyme A (CoA) to form acyl-CoA, which generates branched-chain esters by AAT catalysis [37]. Studies have shown that changes in the enzyme activities of the various synthetic pathways and sharp increases in free amino acid content during fruit ripening are possible reasons for the higher number of esters and the obvious aroma associated with fruit during ripening [21; 38]. Terpenoids are the most diverse secondary metabolites and tend to have low aroma thresholds and characteristic aromas. Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), with C5 structures, act as the main synthetic precursors of terpen, with the main synthetic pathways proceeding through methylerythitol phosphate (MEP) and mevalonic acid (MVA), among which monoterpens (C10), diterpenes (C20), and tetraterpene (C40) are mainly formed through the MEP pathway, while sesquiterpenes and triterpenes are mainly associated with the MVA pathway [26; 39]. In this study, three monoterpens (\(\beta\)-ionone, dihydro-\(\beta\)-ionone, and geranyl acetone), three sesquiterpenes (cis-\(\alpha\)-bergamotene, farnesene, and cis-bisabolene), and one cyclovanilene derivative (theaspirane) were detected, with DY containing more monoterpenes and DM containing more sesquiterpenes and theaspirane. \(\beta\)-Ionone is a monocyclic monoterpene and an end-loop analog of \(\beta\)-carotenoids extensively found in fruits and vegetables, and it forms the basic structures of retinoic acid, retinol, beta-carotene, and vitamin A [40]. According to previous studies, \(\beta\)-ionone not only exhibits outstanding woody incense properties but also possesses significant pharmacological properties, including anti-inflammatory, antibacterial, and anticancer activities [30; 41]. Dihydro-\(\beta\)-ionone is a monocyclic monoterpene compound with a strong cedar aroma that is often detected in _Osmanthus fragrans_ flowers and tea [42; 43]. Geranyl acetone is an acyclic monoterpene characterized by a rose and green fragrance; it has also been detected in blueberries and grapes [25; 44; 45]. Cis-\(\alpha\)-bergamotene and cis-bisabolene were detected only in DM; the latter is a monocyclic sesquiterpene that exhibits antitumor, antifungal, and antimicrobial activities [46]. As an acyclic sesquiterpene, farnesene, which is an intermediate in the synthesis of vitamins E and K1, is the most abundant sesquiterpene (among cis-\(\alpha\)-bergamotene, farnesene, and cis-bisabolene) [47].