Technical Abstract: Tea leaves produce secondary metabolites that are involved in the defense of the plants against invading pathogens. In the case of green teas, these metabolites are polyphenolic compounds called catechins. In previous studies, we developed a mathematical formula called functional mathematical index (FMI) that was used to describe the quality of different olive oils and potatoes in terms of compositional parameters and antioxidative properties of individual components. In this study, we extended the development of the FMI concept in order to define an “optimum tea” based on reported relationships between the content of structurally different catechins of a large number of teas and their dual beneficial effects: antimicrobial activities against a foodborne pathogen and inhibition of human cancer cell lines. The described mathematical approach may be useful for predicting relative beneficial effects of new teas based on their catechin content.