Purification of polyphenols from green tea leaves by ultrasound assisted ultrafiltration process

Application of ultrafiltration membranes is a promising alternative to recovery target components from natural substrates, but some drawbacks should be considered such as the membrane fouling. Here we propose the application of the ultrasound assisted ultrafiltration process for the purification of phenolic compounds from green tea extract. Comparison between the processes with and without ultrasound showed that the state steady flux through the membrane of 5 kDa was 4 times greater in the ultrasound assisted process than in the process without ultrasound. This flux improvement is associated with the decrease in cake formation and in the total resistance (from 17.8 to 10.2 × 1013 m−1). The flux decay profiles were better described by pore blockage models than by the cake formation model, since the cake was formed in the first minutes of filtration and, after that, the particles of relative small size entered in the membrane pores. Moreover, the ultrasound facilitated the permeation of phenolic compounds through the membrane. Comparison between ultrafiltration membranes of different MWCO suggests that the membrane of 20 kDa presented high purity of catechin components in the permeate (49% of EGCG related to the total polyphenol content). Turbidity values of ultrafiltration permeates remained lower than 5 NTU after 30 days of storage under refrigeration and any tea cream formation was observed, which suggests great permeate stability. Thus, the ultrasound assisted ultrafiltration process with the membrane of 20 kDa is suggested for the purification of phenolic compounds from green tea extract in order to ensure great permeate flux, purity of phenolic compounds and extract stability.