We theoretically study the loading of a two-species Bose–Einstein condensate to an optical lattice in a tightly confined one-dimensional trap. Due to quantum fluctuations, the relative inter- and intra-species phase coherencebetween the atoms and the on-site atom number fluctuations are reduced in the miscible regime. For the immiscible case the fluctuations are enhanced and the atoms form metastable interleaved spatially separated domains where the domainlength and its fluctuations are affected by quantum fluctuations.