Temporal kinetics of changes in color, phytochemicals, γ-aminobutyric acid, enzyme activity and antioxidant activity of coffee leaves during postharvest storage

Abstract

Understanding the kinetics of changes in the quality attributes and enzyme activity of coffee leaves during storage is essential to preparing high-quality coffee leaf tea. In the present study, the impacts of different storage temperatures and times on the color, phytochemical composition, amino acids, the activity of enzymes (glutamate decarboxylase (GAD), diamine oxidase (DAO), polyamine oxidase (PAO), γ-aminobutyraldehyde dehydrogenase (AMADH), γ-aminobutyric acid transaminase (GABA-T), glutamate dehydrogenase (GDH), polyphenol oxidase (PPO), and peroxidase (POD)), and antioxidant activity of coffee leaves were investigated. The results showed that low-temperature storage effectively delayed the production of browning color and retained nutrients and antioxidant activity in coffee leaves during storage. The content of 5-caffeoylquinic acid (5-CQA) decreased by 43.5%, 31.1%, and 17.5% when coffee leaves stored for 7 d at 25, 4, and -20 ℃, respectively. The total phenolic content (TPC) and antioxidant activity had negative correlation with the storage time and the activities of PPO and POD were enhanced with prolonged storage time and higher storage temperature. The content of γ-aminobutyric acid (GABA) increased (2.45–3.32 folds) when stored at -20 ℃ within 21 d, which was associated with the decrease of glutamic acid content and the increased activity of GAD. The kinetics of changes in color index L*, total color change (ΔE), TPC, and ABTS and DPPH scavenging capacities fitted the first-order kinetic model and the activation energies ranged from 15.66 to 24.67 kJ/mol, indicating that coffee leaves are prone to deterioration during storage, especially at high temperature. This study indicates that low-temperature storage can effectively prevent the quality loss of coffee leaves while increasing the bioactive compound GABA.