Extraction of antioxidants and caffeine from green tea (Camelia sinensis) leaves: kinetics and modeling.

The effects of temperature (50, 60, 70, 80, 90 °C) and time (5, 10, 20, 40, 80 min) on catechins and caffeine solubility in water from Iranian green tea were investigated, The best combinations of temperature and time extraction with water were 20-40 min, 80 °C for epigallocatechin (EGC), epicatechin (EC) and caffeine (Caff), and 80 min, 90 °C for catechin (C), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG). A mathematical model derived from Fick's second law was then used to calculate the diffusivity of the components, and to monitor the effect of temperature on the diffusivities. The extraction of these components is governed by two diffusion processes: fast and slow. The results showed that the intra-particle diffusion was the rate-governing step of the extraction process. The slow stage diffusivities of these components at their optimum extraction temperatures were calculated as: 1.94e-9 (EGC), 8.1e-10 (EC), 3.9e-10 (Caff), 1.34e-8 (C), 4.2e-9 (ECG) and 4.63e-9 (EGCG).