In modeling turbulent reactive flows based on the transport equation for the joint probability density function (jpdf) of velocity and composition, the change in fluid composition due to convection and reaction is treated exactly, while molecular mixing has to be modeled. A new mixing model is proposed, which is local in composition space and which seeks to address problems encountered in flows with simultaneous mixing and reaction. In this model the change in particle composition is determined by particle interactions along the edges of a Euclidean minimum spanning tree (EMST) constructed in composition space. Results obtained for the model problem of passive scalars evolving under the influence of a mean scalar gradient in homogeneous turbulence are found to be in reasonable agreement with experimental findings of Sirivat and Warhaft (1983). The model is applied to the diffusion flame test model problem proposed by Norris and Pope (1991) and its performance is found to be superior to that of existing models. The essential feature of the new EMST mixing model, which accounts for its success in the diffusion flame test, is that mixing is modeled locally in composition space.