The formulation of bioactive powders is crucial to their property, functionality and bioaccessibility. This study investigated the incorporation of Ca-2(+) as a protectant aid for producing active dry probiotics via spray drying, and explored the mechanism underlying the positive effect of Ca2+ on cell viability. At inlet temperature of 98 degrees C and outlet temperature of 65 degrees C, supplementing 1 mM CaCl2 to either 10 wt% lactose or 10 wt% trehalose solution increased the survival ratio of Lactobacillus rhamnosus GG ( LGG) from 5% to 30%. The growth capability of dried LGG was also enhanced in the presence of calcium. Powder properties including particle morphology, amorphous state and infrared spectrum were minimally influenced at such a low Ca2+ loading. By contrast, adding 1 or 100 mM Ca2+ in reconstitution solution or MRS agar plates notably improved the survival of LGG cells during single droplet drying with pure lactose protectant. The findings suggested that the protective mechanism of Ca2+ is based on enhancing the intrinsic tolerance of LGG cells, rather than modifying the powder properties. Given the protective effect of Ca2+ on probiotic cells under stressful conditions, calcium-containing dry probiotic products that confer duel benefits to consumers may be developed as new types of functional foods. (C) 2018 Elsevier B.V. All rights reserved.