Separation and characterization of spontaneously assembled nano-aggregates in natural green tea infusions

For the fast and efficient separation of spontaneously assembled nano-aggregates from natural tea infusions and for the preliminary characterization of their physicochemical and phytochemical profiles,ultrafiltration was performed to separate nano-aggregates naturally existed in green tea infusions of 1∶ 50 tea-water ratio from Camellia sinensis,assisted with centrifugation. Initially,the impacts of molecular weight cut-off of ultrafiltration membranes,centrifugal forces and centrifugal time on the scattering intensity,average diameter of tea nano-aggregates separated were analyzed by dynamic light scattering,while their Zeta potentials and conductivities were determined via laser Doppler Velocimetry. On this basis,tea polyphenols,proteins,carbohydrates,catechins and methylxanthines in nano-aggregates separated with ultrafiltration membranes of different MWCO were detected with high performance liquid chromatography and ultraviolet and visible spectrophotometer,in order to elucidate the chemical composition of green tea nano-aggregates and to characterize the distribution features of various chemical components in nano-aggregates. A large number of negatively-charged nano-aggregates of300 nm in diameter were confirmed in drinkable green tea infusions at 25 ℃. In addition,these colloidal particles were successfully obtained by ultrafiltration membranes of 100 ku in MWCO assisted with centrifugation of 4000 × g for 20 min.Furthermore,proteins,carbohydrates and tea polyphenols were indicated to construct the main body of green tea nano-aggregates,though catechins and methylxanthines were also found in these particles. In conclusion,a combination between ultrafiltration and centrifugation provided an effective method for the separation of green tea nano-aggregates.These peculiar nano-colloidal particles were composed of tea polyphenols,proteins and carbohydrates.