Hodge-theoretic mirror symmetry for a Calabi-Yau mirror pair says that the variation of Hodge structure arising from quantum cohomology of a Calabi-Yau manifold and that arising from deformation of complex structures on the dual Calabi-Yau manifold can be identified with each other, and it has been conjectured (Gamma-conjecture) that the Gamma-integral structure in quantum cohomology corresponds to a natural integral structure on the mirror side. Here the Gamma-integral structure is defined via the topological K-group and the Gamma-class, a characteristic class with transcendental coefficients containing the Riemann $\zeta$-values. In this article, we explain an approach to the Gamma-conjecture using tropical geometry and observe that the Riemann $\zeta$-values arise as error terms of tropicalization in the computation of mirror periods. This is based on joint work [AGIS] with Abouzaid, Ganatra and Sheridan.