Modulation of Biochemical Traits in Cold-Stored ‘Karaerik’ Grapes by Different Edible Coatings

Understanding the effects of edible coatings on postharvest quality and shelf life of ‘Karaerik’ grapes is crucial for improving storage outcomes and reducing losses. However, limited information exists regarding the effectiveness of different coating materials on this regionally significant variety. In this study, ‘Karaerik’ grapes were treated with carboxymethyl cellulose (CMC) and locust bean gum (KB) coatings and stored under cold conditions (0 ± 0.5 °C, 90–95% relative humidity) for 0, 25, 45, and 60 days. Storage duration and coating treatments significantly affected most physical, physiological, and biochemical parameters. During storage, grape weight loss progressively increased, reaching 9.60% in the control by day 60. Coatings slightly reduced this loss, with KB showing the lowest (5.11%) compared to the control (5.69%). Respiration initially declined but surged again at day 60, especially in the control (96.4 μmol CO2/kg·hour), while coatings helped mitigate this rise. Ethylene release remained unchanged. A slight pH decline (~4.6%) was observed in the control, while KB-treated grapes maintained higher pH and lower acidity. Soluble solids remained stable across treatments. Color changed notably during storage: a* nearly doubled (more redness), b* increased (less blue), and chroma (C*) declined by ~25%, especially in uncoated grapes. Total sugar dropped by ~43% in KB-treated grapes, with the control retaining the most. Tartaric acid decreased by ~55%, notably in KB samples. Antioxidant activity and total phenolics declined significantly (~66%) in the control. CMC coating better-preserved antioxidant capacity, while the control showed the highest phenolic levels overall. Ferulic, gallic, and chlorogenic acids increased toward the end of storage, particularly in coated grapes. In contrast, rutin and vanillic acid peaked mid-storage and were better preserved in the control. The heatmap showed significant metabolite changes in fruit samples across 0D, 25D, 45D, and 60D storage periods under CMC, CNT, and KB treatments, with distinct clustering patterns revealing treatment-specific biochemical responses. The correlation matrix revealed strong positive relationships (r > 0.70) between total sugar, glucose, and fructose levels, while ethylene showed significant negative correlations (−0.65 to −0.85) with maturity index, pH, and total soluble solids, indicating interconnected metabolic pathways during fruit ripening and storage. We conclude that edible coating selection significantly influences grape biochemical stability during cold storage, with CMC emerging as a superior choice for maintaining certain quality parameters. © 2025 by the authors.