Effect of energy level on reactive oxygen species metabolism during shade-drying of Thompson seedless grapes and its relation to browning.

The browning of Thompson seedless grapes during shade-drying significantly hampers the sustainable and healthy development of the industry. This study investigates the browning phenomenon and reactive oxygen species (ROS) dynamics when Thompson seedless grapes, treated with adenosine triphosphate (ATP), 2,4-dinitrophenol (DNP), and water (QS), are dried in the shade. The effects of these treatments on ROS metabolism were analyzed through physiological, biochemical, and proteomic analyses. The findings showed that ATP treatment markedly delayed the increase in browning and reactive oxygen content, maintained high activity levels of ROS scavenging enzymes (superoxide dismutase and peroxidase), reduced malondialdehyde production-a membrane lipid peroxidation product-and preserved cell membrane integrity compared to QS and DNP treatments. Proteomic analysis identified three biological pathways involved in ROS metabolism in Thompson seedless grapes: glutathione metabolism, ascorbic acid, and glyoxalate metabolism, and peroxisomal pathways. Exogenous ATP treatment upregulated the expression of 17 proteins (SOD, APX, GPX, GST, GR), with significant increases in GST2 (D7SKQ2), POD1 (F6H095), SOD3 (D7TI74), and SOD4 (F6HTX9) by 1.707, 1.589, 1.644, and 2.213-fold, respectively. Therefore, ATP treatment maintains ROS scavenging proteins' expression, reduces the accumulation of ROS, maintains a balance in ROS metabolism, maintains the cell membrane stability and suppresses the oxidation of lipids, thus delaying the browning of Thompson seedless grapes. These findings are significant for regulating browning in the shade-drying process of Thompson seedless grapes.