Passion fruit peel (PFP) is a common byproduct of industrial passion fruit processing, yet it serves as a valuable source of diverse bioactive compounds and nutrients. However, limited attention has been paid in the literature to the nutritional properties and practical applications of PFP. This review summarizes methods for extracting bioactive substances from PFP, examines their potential health benefits, and explores their prospects for utilization in the food industry. Recent studies have quantified various bioactive components, such as flavonoids, vitamins, and dietary fiber (DF), while reporting the corresponding extraction yields or concentrations. Furthermore, these compounds exhibit significant potential in promoting human health, including antioxidant, anti-inflammatory, and gut health-improving effects. The analysis also highlights the bioavailability of bioactive constituents in PFP. Consequently, PFP presents a promising yet underexplored area for scientific research, though substantial challenges remain in optimizing its utilization, enhancing extraction efficiency, and advancing innovative applications.

‘Fengtang’ plum, a specialty fruit variety from Guizhou Province, is characterized by its high total soluble solids (TSS) and well-balanced sugar–acid ratio. In this study, widely targeted metabolomics (UPLC-MS/MS) combined with multivariate statistical analysis was employed to systematically monitor dynamic changes in sugar–acid metabolism across three critical developmental stages of the fruit: pre-veraison stage (PR), veraison stage (VR), and full veraison stage (FR). The aim was to elucidate the intrinsic mechanisms underlying high sugar accumulation. The results indicated that TSS content increased significantly during fruit maturation, reaching up to 17%, while titratable acid (TA) content continuously decreased. Consequently, the sugar–acid ratio rose substantially from 21.5 at the early stage to 43.8. A comprehensive metabolomic analysis led to the identification of 2003 metabolites, with notable emphasis on phenolic acids, amino acid derivatives, sugars, and other major classes. Key metabolic pathways from the KEGG database were also examined. Enrichment analysis of these pathways revealed that central metabolic routes—including fructose and mannose metabolism, galactose metabolism, and the tricarboxylic acid (TCA) cycle—played crucial roles in the dynamic accumulation of sugar–acid components. Notably, oligosaccharides such as cottonseed sugar and pine trisaccharide were observed to accumulate significantly during fruit ripening. These findings clarify the metabolic foundation and mechanisms contributing to the high sugar quality of ‘Fengtang’ plum, thereby providing a theoretical basis for precise fruit quality regulation and the optimization of post-harvest preservation strategies.

Harvest maturity critically determines the balance between eating quality (evaluated by soluble solids, sugars, acidity, and firmness) and nutritional bioactive compounds in fleshy fruits, yet the optimal window for ‘Fengtang’ plum—a high-sugar cultivar from Guizhou—remains unclear. This study systematically investigated the dynamic changes in fruit quality traits, flavonoid accumulation, antioxidant activity, and their underlying regulatory mechanisms across three on-tree maturity stages (PG, PB, and PY) using integrated metabolomic and transcriptomic approaches. As ripening progressed, soluble solids, soluble sugars, and reducing sugars increased significantly while firmness and titratable acidity declined, optimizing fresh-eating quality at the PY stage, whereas total flavonoid content and DPPH/ABTS antioxidant activities continuously decreased, peaking at the PG stage. Metabolomic analysis identified 35 differentially accumulated flavonoid-related metabolites, comprising 32 reliably annotated flavonoids and 3 tentatively annotated xanthones (MSI Level 3); the reliably annotated flavonoids, particularly flavan-3-ols and flavonols, exhibited persistent downregulation, whereas only a few, including dihydromyricetin-3-O-glucoside and apigenin-5-O-glucoside, showed PY-specific upregulation. Transcriptomic profiling revealed systemic reprogramming of the R2R3-MYB transcription factor family: the progressive downregulation of positive regulators, coupled with the PY-stage upregulation of repressive MYBs, was associated with the overall decline in flavonoid biosynthesis, while certain branch-specific MYBs positively correlated with the few upregulated flavonoid components, suggesting a possible association with localized activation of specific metabolic branches against a background of global downregulation. Collectively, these findings delineate a trade-off pattern between edible quality improvement and bioactive compound decline during ‘Fengtang’ plum ripening and establish a MYB-mediated regulatory network model, providing a theoretical basis for tailoring harvest timing according to industrial end-use and offering candidate gene resources for molecular breeding aimed at nutritional quality enhancement.