Effect of Pre-drying Treatments and Storage on Color and Phenolic Composition of Green Honeybush (Cyclopia subternata) Herbal Tea

摘要

The effect of various pre-drying treatments and storage temperatures on the color (L.*, a*, b*, chroma, and hue angle) and phenolic composition of green Cyclopia subternata was investigated. Pre-drying treatments, which included comminution + drying (T2), steaming (ca. 90-93°C/60 s) + comminution + drying (T3), and comminution + steaming + drying (T4), had a detrimental effect (p < 0.05) on the color parameters relative to the control (T1) (drying of intact leaves). All drying took place at 40°C and 30% relative humidity (RH). Of the pre-drying treatments (T2, T3, and T4), the best retention of the green leaf color was observed for T3 (p < 0.05). T2 reduced the SS and TP contents of the leaves (p < 0.05) as well as the content of individual phenolic compounds, including mangiferin, isomangiferin, and eriocitrin. Scolymoside did not follow the same trend as the other compounds, with the intact leaves having the lowest content. It is postulated that oxidation of eriocitrin (eriodictyol-7-O-rutinoside) to scolymoside (luteolin-7-O-rutinoside) occurred with comminution and steaming. The phenolic composition of samples, subjected to T1 and T3 and a 6 month storage period at 0 and 30°C, remained stable. Storage at 30°C resulted in detrimental color changes, leading to the loss of the green leaf color irrespective of the pre-drying treatment.