Sulfur dioxide delays quality deterioration by maintaining energy metabolism and mitochondrial structure in postharvest table grapes

BACKGROUND: Table grapes are very susceptible to rapid softening, browning, and decay after harvest, which significantly reduces their commercial value. Sulfur dioxide (SO₂) treatment is used widely to mitigate these postharvest losses; however, the biological mechanisms underlying its preservative effects remain poorly understood. This study aimed to elucidate how SO₂ preserves postharvest fruit quality by modulating energy metabolism in ‘Munage’ grape berries (Vitis vinifera L. ‘Munage’). RESULTS: Sulfur dioxide fumigation (500 μL L⁻¹) effectively maintained the visual quality of grapes during 60 days of storage at 0 °C, reducing decay incidence and delaying firmness loss. It also preserved soluble solids content and titratable acidity. Further analysis showed that SO₂ treatment maintained cellular energy status by upregulating the expression of energy metabolism-related genes, enhancing nicotinamide adenine dinucleotide (NAD) kinase (NADK) activity, increasing the H⁺-ATPase, Ca²⁺-ATPase, and cytochrome c oxidase activity, and delaying the decline in energy charge. Sulfur dioxide also elevated cellular levels of key TCA cycle intermediates (pyruvate, citrate, malate, and succinate) through modulation of enzymatic activity and gene expression. Transmission electron microscopy showed that SO₂ preserved mitochondrial membrane integrity and cristae structure while reducing 8-hydroxy-2′-deoxyguanosine (8-OHdG) accumulation and mitochondrial swelling. CONCLUSION: Sulfur dioxide treatment delayed postharvest quality deterioration in grapes by modulating the TCA cycle, preserving mitochondrial structure and function, and mitigating cellular energy loss. These findings provide mechanistic insights into the preservative role of SO₂ and support its application to improve the storability and marketability of table grapes.