Estimates of Catechins Content in Green Tea: A Review Based on Meta-analysis

Green tea is known for its unique health benefit and flavor. As one of the major bioactive and taste components in green tea infusion, catechins have been deeply studied worldwide. However, the reported contents differ significantly in research, thus needing further study for estimates. Here, we systematically reviewed 11 012 English articles from the Web of Science Core Collection and extracted 40 from them based on meta-analysis. All 40 studies were reported by organizations from 14 countries with green tea samples from 13 countries and regions. Among them, 35% of the studies were from Chinese scientific research institutions, and 75% of the research used samples from China. More than half of these studies did not measure the moisture content in green tea samples or crush the samples to make the particle size consistent; one-tenth of the studies referenced ISO 14502-2:2005; while 70% used water as the solvent. The catechins content in 32 studies was between 5% and 20% of sample weight, and their corresponding pretreatment and extraction treatment were analyzed. The statistics indicate that catechins content may be significantly affected by different extraction solvents and neo-standardization for extracting catechins is necessary according to research needs.