This study is designed to identify strategies for substituting or reducing the use of sulfur dioxide (SO₂) while improving the quality of semi-sweet wines. Using the ‘Petit Manseng’ semi-sweet wine as the research object, the effects of different concentrations and combinations of glutathione (GSH), mannan (Man), vitamin C (VC), chitosan oligosaccharide (COS), and SO₂ were investigated. The results show that under VC treatment, the DPPH free radical scavenging rate of the wine is higher than that of other antioxidant treatments, with the V-1 treatment being 16.9% higher than the CK treatment. The wine treated with 30 mg/L of SO₂ has the highest reducing power. After COS treatment, the wine color deepens, making it unsuitable for sweet white wines. GSH and Man can delay the increase in OD240 and the decrease in total phenolic. Man can increase the content of sweet amino acids such as serine. The treatments with man and GSH result in a greater variety of aromatic compounds and higher content of epigallocatechin. The combination treatment of GSH, Man, and SO₂ resulted in semi-sweet wines with a bright color, rich aroma, and full-bodied, balanced taste, achieving the best quality indicators and the highest sensory evaluation. This wine exhibits a light yellow color, full body, and a complex, balanced aroma, which are improvements in quality compared to semi-sweet wines with 30 mg/L of SO₂ added, and it reduces the use of SO₂ by 33.3%. This study shows that adding 5 mg/L of GSH, 5 mg/L of Man, and 20 mg/L of SO₂ can significantly improve the antioxidant properties and quality of semi-sweet wines.

To dissect the genetic trends of phenolic compounds in wine grapes and identify key regulatory genes for epicatechin (EC) synthesis, this study used an F1 population derived from ‘Pinot Noir’ × ‘Marselan’ as material. SSR molecular markers were used to verify the authenticity of hybrid offspring, and genotyping by target sequencing (GBTS) combined with genome-wide association study (GWAS) was employed to locate EC-related loci. The candidate gene VvCHR5 was then cloned, subjected to expression analysis, and functionally validated through Agrobacterium-mediated transient overexpression in grape berries. The results showed that 281 true hybrids were identified from 305 progeny, with a true hybrid rate of 92.13%. In F1 seeds, proanthocyanidins showed moderately high inheritance, and total flavonoids tended toward intermediate-to-low inheritance. Seeds were the main site of tannin accumulation, with C, EC, and EGC as the core monomers. GWAS detected three EC-related SNP loci distributed on Chr1, Chr6, and Chr12, and candidate genes such as VvCHR5 were identified. Transient overexpression of VvCHR5 significantly promoted EC accumulation in ‘Muscat Hamburg’ seeds. On day 4 after injection, EC increased to approximately 15 times the level of the empty vector control; on day 8, it remained significantly higher than the control, with an increase rate of approximately 326.72%. These findings suggest that VvCHR5 may affect EC accumulation by altering carbon flux within the flavonoid metabolic pathway, providing loci, genes, and materials for molecular breeding of phenolic quality in wine grapes.