Introduction

Sweet cherry (Prunus avium L.), a member of the Rosaceae family, is among the most widely consumed fruits globally due to its appealing flavor and aroma. Sweet cherries are rich in bioactive compounds such as anthocyanins, polyphenols, and melatonin. Due to their antioxidant and anti-inflammatory properties, these compounds play a significant role in reducing the risk of cardiovascular diseases, cancer, and joint inflammation. However, its postharvest quality rapidly deteriorates as a result of physiological disorders such as shriveling, surface pitting, bruising, and stem browning. The application of bioactive compounds during the postharvest stage of horticultural crops represents a novel approach in sustainable agriculture. This strategy can enhance product quality by reducing losses, extending shelf-life and storage duration, and preserving the antioxidant system. Such treatments aim to improve marketability, meet consumer preferences, and increase export potential. The present study was designed to evaluate the effects of postharvest dopamine application, a compound with recognized antioxidant activity, on quality preservation, senescence delay, shelf-life extension, and the enhancement of antioxidant enzyme activity in sweet cherries during cold storage.



Materials and Methods

On June 21, 2023, sweet cherry fruits (Prunus avium L. cv. Tak Daneh) at the fruit color maturity stage, were harvested from an orchard located in Saqqez, Kurdistan Province, and immediately transported to the Postharvest Physiology Laboratory, Department of Horticultural Sciences, University of Zanjan, Zanjan, Iran. Uniform fruits in terms of color and size were immersed for 20 minutes in dopamine solutions at concentrations of 0, 50, 100, and 200 µM (Sigma Chemical Co.) supplemented with two drops of Tween-20. The experimental design was factorial based on a completely randomized design with three replications, each containing 20 fruits. Subsequently, groups of 20 fruits were placed in polyethylene containers (25 × 15 × 5 cm) and stored at 1 ± 0.5 °C with 85 - 90% relative humidity. Sampling was conducted after 7, 14, 21, and 28 days of storage, and the physicochemical attributes of the fruits were evaluated following 24 hours of equilibration at room temperature. In addition, three freshly harvested, untreated fruits were considered as the control group (day 0) without treatment and without cold storage. Statistical analysis of the data was performed using SPSS (version 26) and Graphs were plotted using Microsoft Excel 2019. Mean comparisons were performed using the Duncan’s multiple range test at p < 0.05 probability level.



Results and Discussion

Analysis of variance (ANOVA) indicated that both the individual effects of treatment and storage duration, as well as their interaction, significantly influenced the flesh browning index (FBI), the stem browning index (SBI), stem chlorophyll content (TChl), weight loss (WL), electrolyte leakage (EL), malondialdehyde (MDA), proline content, hydrogen peroxide (H2O2) level, and the activity of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) (p < 0.01). In contrast, the interaction between treatment and storage time did not significantly affect fruit firmness, although the main effects of treatment and storage duration were significant at the 1% level. The results of mean comparison demonstrated that the highest activity of superoxide dismutase and catalase enzymes, along with the lowest levels of malondialdehyde, hydrogen peroxide, and ion leakage, were observed in the treatment with 200 μM dopamine. In contrast, the concentration of 100 μM induced the maximum activity of peroxidase and ascorbate peroxidase enzymes. These biochemical changes were associated with maintained tissue firmness, delayed flesh browning, and reduced stem discoloration. As a catecholamine, dopamine exhibits strong antioxidant activity. It enhances the efficiency of the reactive oxygen species (ROS) scavenging system by increasing the activity of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, while simultaneously reducing hydrogen peroxide accumulation. This mechanism ultimately leads to decreased levels of superoxide and hydrogen peroxide. Overall, postharvest dopamine application reduced senescence and stem browning in 'Tak Daneh' sweet cherry and improved key biochemical attributes related to fruit quality and stress tolerance.



Conclusion

In conclusion, exogenous dopamine treatment contributed to the retention of fruit firmness and delayed senescence by reducing electrolyte leakage (EL), malondialdehyde (MDA), and H2O2 accumulation (notably at 200 µM), while enhancing antioxidant enzyme activities, including SOD and CAT (200 µM), and POD and APX (100 µM); also, proline content (200 µM), thereby supporting chlorophyll preservation in the stem.