A mathematical model for prediction of moisture content in apple and pineapple during osmo-concentration was developed using both water loss and sugar gain as input variables. The model predicts theoretical maximum water loss from osmotic pressure equilibrium considerations. Using water diffusivity and 'sugar-water diffusion quotient' as the primary variables, sugar diffusivity, sugar gain, water loss and moisture contents could be predicted at different temperatures (30, 40 and 50 degreesC) and concentrations (50, 60 and 70degreesBx) of sucrose solution. Theoretical maximum water loss was found to vary between 0.69-0.81 kg water kg slice(-1) for apple and 0.64-0.77 kg water kg slice(-1) for pineapple. Predicted values of water diffusivity varied between 0.78-3.46x 10(-10) m(2) s(-1) for apple and 1.90-4.35 x 10(-10) m(2) s(-1) for pineapple. The average value of `sugar-water diffusion quotient' was found to be 3.53 +/- 0.652 and 4.07 +/- 0.776 for apple and pineapple, respectively. The actual and predicted values of moisture contents in the two fruits were found to have good agreement with a relative deviation percent below 10%. (C) 2004 Elsevier Ltd. All rights reserved.