Characterization of the Aromatic Profile of Mature-Green Tomato Fruit (‘Fen Junmei’) in Response to Supplemental LED Light Quality and Intensity During Ripening

Light quality and light intensity, as important environmental signals, can regulate the ripening process and flavor compound synthesis in tomato fruits. Chitosan oligosaccharides, as natural bio-stimulants, can improve postharvest quality of fruits and vegetables. However, how varied LED light quality–intensity regimes modulate ripening and aroma metabolism in chitosan-oligosaccharide-pre-treated mature-green tomato fruit remains unclear. This study used mature-green tomato fruits as experimental material, which were pre-treated by immersion in chitosan oligosaccharide solution. Subsequently, different combinations of supplemental light qualities (white light, blue light, and 1:1 red–blue composite light) and varying light intensities were applied for continuous illumination. The effects of these lighting conditions on the postharvest physiological quality and volatile aroma components of tomatoes were systematically investigated, and the molecular regulatory mechanisms were analyzed through transcriptome sequencing. The results showed that light quality and intensity significantly regulated tomato fruit color change, firmness, pigment accumulation, and sugar–acid quality. High-intensity red–blue combined light treatment (RB-H) effectively accelerated fruit ripening, promoted carotenoid accumulation, significantly increased the content of terpenes and aromatic volatile compounds, and improved fruit flavor. Transcriptome analysis revealed that different light treatments induced a large number of differentially expressed genes, with transcription factors from the WRKY, MYB, AP2/ERF, bHLH, NAC, and C2H2 families widely involved in light signal responses. Weighted gene co-expression network analysis (WGCNA) identified two key modules associated with light response. KEGG pathway enrichment analysis revealed that the biosynthesis of the terpenoid backbone, monoterpenoid biosynthesis, sesquiterpenoid and triterpenoid biosynthesis, as well as tyrosine metabolism pathways, are the core pathways regulating the production of volatile aroma compounds in tomatoes. In summary, RB-H treatment promotes the accumulation of characteristic aromatic compounds and enhances overall tomato quality by activating key genes involved in terpenoid biosynthesis and tyrosine metabolism pathways. This study reveals the transcriptional regulatory network by which light quality and intensity shape postharvest tomato ripening and flavor development in chitosan-oligosaccharide-pre-treated fruit, providing theoretical support for precise LED light environment control and targeted improvement of flavor quality in postharvest tomatoes.