## 3 Results and Discussion
### Differential Volatile Aroma Screening and OPLS-DA Analysis of VOCs during Ripening of R. roxburghii
(**A**) Clustering heat map; (**B**) score plot (R\({}^{2}\)X = 0.995, R\({}^{2}\)Y = 0.921, Q\({}^{2}\) = 0.817); (**C**) 200 permutation test cross-validation plot (R\({}^{2}\) = 0.0722, Q\({}^{2}\) = \(-\)0.85); and (**D**) VIP diagram, red bars represent VOCs with VIP value over 1.  
other stages. In particular, 1-nonanol (ROAV > 100) imparted a significant fat flavor during this stage. The volatiles identified in stage IV were predominantly alkenes, with (Z)-\(\beta\)- ocimene being particularly prominent, exhibiting an ROAV greater than 1000, which contributed to the fruit's strong citrus aroma. Notable compounds such as styrene (ROAV > 100), cyanophyllene oxide (ROAV > 1), and p-mentha-1,3,8-triene (ROAV > 1) were also present, imparting balsamic, sweet and fat notes, respectively. Although the presence of aldehydes was limited, \(\beta\)-cyclodextrin, 2- (E)-hexenal, and hexanal were found at high levels, each exhibiting distinctive characteristics: both 2- (E)-hexenal and hexanal were notably high, with ROAVs exceeding 1000, contributing fruit and grass flavors, respectively. Interestingly, the concentrations of these aldehydes demonstrated a pattern of initial increase followed by a decrease during the ripening process of _R. roxburghii_, which might be associated with the catalytic effect of 2-enal reductase and the interaction of aldehydes with amines and sulfhydryl groups in proteins [61; 62]. Regarding esters, while their presence was limited at this stage, ethyl caprylate significantly enhanced the fruit flavor (ROAV > 1000). The synergistic effect of these volatiles collectively contributed to the unique flavor profile of _R. roxburghii_ fruits at stage IV. In the cluster analysis of cluster 2.1, stage V exhibited a distinctive composition of volatile substances, predominantly characterized by alkenes, esters, and ketones. Among the alkenes, terpen are the principal secondary products of the acetyl-CoA metabolic pathway in plants [63; 64]. These terpen contributed complex aromas, including wood, citrus, and lemon, and were represented by compounds such as \(\beta\)-caryophyllene, \(\alpha\)-caryophyllene, 4-isopropyltoluene, and \(\alpha\)-terpinene. Esters primarily enhanced fruit and citrus aromas, with ethyl hexanoate and isoamyl acetate exhibiting ROAV values significantly exceeding 1000, thereby serving as the main flavor contributors at this stage. Additionally, 2-methylbutyl acetate, methyl hexanoate and caprylic acid methyl ester were present at significant levels (ROAV > 100), further enriching the aroma profile of _R. roxburghii_ fruit. Ketones were closely correlated and categorized together, predominantly comprising fatty acid derivatives. Compounds such as 6-methyl-5-hepten-2-one, ethyl vinyl ketone, and 2-heptanone exhibited a range of aromas, including mushroom, pungent, and soap, respectively. High ROAV components such as \(\alpha\)-ionone, \(\beta\)-Ionone, and 4-methoxy-2,5-dimethyl-3 (2H)-furanone impart wood, flower, and caramel aromas, respectively, and are generally considered direct products of the oxidative cleavage of carotenoids [65]. Furthermore, sweet aromas were primarily attributed to neraniol, benzaldehyde, 4-methoxy-2, 5-dimethyl-3 (2H) -furanone, and 4-allylanisole, with 4-allyl anisole being particularly noteworthy due to its low threshold and high ROAV value (>1000), making it a significant sweetening component. However, stage V was also associated with the emergence of undesirable odors, as the levels of acids such as nonanoic acid, octanoic acid and hexanoic acid peaked during this stage, which negatively impacted the overall flavor. As a by-product of fatty acid metabolism, alkanes are primarily derived from fatty acids through the fatty acyl-CoA pathway, which is characterized by a low boiling point and minimal contribution to aroma [66]. Consequently, this pathway does not significantly influence the aroma characteristics of _R. roxburghii_ fruit.