In this paper the analytical solution of a mathematical model of mass transfer in spherical geometry is presented for boundary conditions useful for simulating drying processes of fruit with near spherical stones. This model is applied to analyse the efficiency of a new pre-treatment for a prune drying processes. The new proposed physical abrasion pre-treatment increases the plum drying rate at 60 degreesC. The mathematical model here presented allows a complete comparison of the experimental results obtained with this pre-treatment and with traditional ones. In particular the greater efficiency of the new physical pre-treatment appears to be due to the enhancement of the water diffusivity in the plum skin. The dipping pre-treatment with ethyl oleate gives an enhancement of the diffusivity in the skin too, but it have lower efficiency and implies many problems due to the use of chemical additives. (C) 2003 Elsevier Science Ltd: All rights reserved.