To maintain viable cells over the critical value of 10(6) cfu g(-1) throughout shelf life of probiotic yoghurt, Lactobacillus acidophilus LA-5 was encapsulated by spray drying using whey powder (WP) and gum arabic (GA) mixtures. Box-Behnken Design (BBD) method was used to optimise drying conditions and WP to GA ratio in wall material. Responses were recorded for encapsulation efficiency and production efficiency of microcapsules. Optimum conditions were determined as: inlet air temperature, 140 degrees C; liquid flow rate, 0.485 L h(-1); WP to GA ration 0.83:0.17 (dry weight basis), resulting in 93.95% maximum encapsulation efficiency and 48.36% maximum production efficiency. After exposure to simulated gastrointestinal conditions, the microcapsules produced under optimum conditions provided better protection of L. acidophilus, when compared with free cells, with a reduction of 10.84% and 24.54%, respectively. Particle size of microcapsules was D-50:6.276 mm, which is acceptable for incorporation into dairy and other food products. (C) 2020 Elsevier Ltd. All rights reserved.