Media optimization for elevated molecular weight and mass production of pigment-free pullulan

► A non-pigment producing A. pullulans SZU 1001 was screened by complex mutagenesis. ► Orthogonal array design was introduced for high molecular weight of pullulan. ► Response surface methodology was used to optimize medium for high yield of pullulan. ► The molecular weight and production of pullulan were increased by 97.25% and 11.04%. ► NaCl is the most important factor influencing the molecular weight of pullulan.