Study finds grape berries rewire antioxidant defenses during ripening

A study published Monday in OENO One reports that grape berries manage ripening through a shifting antioxidant system that helps control reactive oxygen species, or ROS, as the fruit matures. The work offers a detailed look at how redox metabolism changes across berry development and could help researchers and growers better understand how grapes maintain tissue function and fruit quality during a period of intense metabolic activity.

The research was led by Luan C. Corrêa, Eduardo Monteiro, Roberta P. da Paschoa, Rodrigo R. R. F. Lucas, Vanildo Silveira and Ricardo Bressan-Smith. It focused on Niagara Rosada, a table grape cultivar described in the paper as a hybrid of Vitis labrusca and Vitis vinifera that is widely grown in Brazil. The authors combined quantitative proteomics with enzyme activity tests to examine the mesocarp, the fleshy inner part of the berry, during key stages of ripening.

Ripening in fleshy fruits is known to involve major changes in sugar accumulation, acid decline, hormone signaling and cell wall remodeling. Those processes raise respiratory activity and other redox reactions, which in turn generate ROS as by-products of normal aerobic metabolism. In excess, ROS can damage proteins, lipids and nucleic acids. But at controlled levels they also act as signals that help regulate development.

The new study set out to test whether grape berries limit oxidative injury during ripening by adjusting both ROS-scavenging enzymes and pathways that generate NADPH, a molecule needed for several detoxification systems. According to the paper, the results support that idea.

The team identified 1,434 proteins in berry mesocarp samples, and 956 of them, or 67%, showed differential accumulation across developmental stages. Functional enrichment analysis found that antioxidant processes were especially prominent, though the dataset also included proteins linked to energy metabolism, hormone metabolism, protein turnover, secondary metabolism and stress responses.

The pattern changed with time. Early stages were marked by stronger accumulation of photosynthetic and energy-related proteins. Later stages showed greater accumulation of antioxidant and stress-related proteins. The authors say this points to stage-dependent reprogramming of the berry proteome as ripening advances.

The enzyme assays matched that broader picture. Catalase showed what the researchers described as a biphasic profile over development. Superoxide dismutase reached its highest activity late in ripening. Peroxidase activity declined progressively. Glutathione reductase and glutathione peroxidase also changed by stage, reinforcing the role of NADPH-dependent detoxification pathways in managing oxidative balance.

Even with signs of increased ROS-related activity, the study did not find evidence of severe tissue breakdown in the mesocarp. Measurements of inorganic phosphate leakage and lipid peroxidation suggested moderate membrane-associated oxidative changes rather than extensive cellular deterioration. In practical terms, the findings indicate that berries can sustain active metabolism during ripening without widespread loss of cellular integrity.

The experiments were carried out on grapes grown in São Fidélis, in Rio de Janeiro state, Brazil, in a vineyard established in 2006. The vines were grafted onto IAC-572 rootstock and trained on a pergola system. Proteomic samples came from one growing cycle from October to December 2022, while enzymatic activity assays were conducted on fruit from another cycle from February to June 2023.

Sampling followed the modified E-L system used in viticulture to classify grape development. The researchers examined berries at pre-veraison, veraison and over-ripe stages for proteomic analysis, with an additional post-harvest stage used only for enzyme assays. For each proteomic replicate, mesocarp tissue from five berries taken from different bunch groups was pooled after skins and seeds were removed.

The paper places the findings within a broader question in plant biology: how fruits preserve redox balance while undergoing rapid biochemical change. Grapes are considered a useful model because they are non-climacteric fruits, meaning their ripening depends less on an ethylene-driven burst than on coordinated shifts in sugars, hormones and signaling pathways. Earlier studies had linked antioxidant enzymes such as catalase and superoxide dismutase to berry development or stress exposure, but many focused on skin tissue, single enzymes or gene expression rather than protein accumulation and enzyme function together.

By integrating proteomic data with biochemical assays, the authors argue that their work provides a more complete framework for understanding redox regulation in grape berry mesocarp. They describe this regulation as a central feature of berry development that supports mesocarp functionality and fruit quality.

That matters beyond plant physiology. Because grape composition at ripening shapes wine quality and stability, a clearer picture of how berries control oxidative stress could eventually help guide vineyard management under heat or other stress conditions that affect fruit chemistry. The study does not test winemaking outcomes directly, but it offers a molecular basis for future work on how redox balance during ripening may influence the raw material used for beverages.

The article was received by the journal on Oct. 31, 2025, accepted on June 12 and published on June 29 in Volume 60, Issue 2 of OENO One.