Optimization of the freeze-drying of marine yeast Sporidiobolus pararoseus ZMY-1 for its application in biocontrol of fungal infections

• S. pararoseus ZMY-1 antagonized A. alternata , P. expansum and B. cinerea in vitro . • S. pararoseus ZMY-1 reduced disease incidences and lesion diameters in apple fruit. • Composite protectant for S. pararoseus ZMY-1 during freeze-drying was optimized. • Formula was 1.5% skim milk powder, 0.1875% polyethylene glycol and 5.25% trehalose. • Freeze-dried yeast kept good biocontrol efficacy and was suitable to store at 4 °C. Penicillium expansum , Botrytis cinerea and Alternaria alternata are three common fungal pathogens infecting a variety of fruit and vegetables, resulting in postharvest decay and huge loss. In this work, the marine yeast Sporidiobolus pararoseus ZMY-1 was studied for its antagonistic effect against P. expansum , B. cinerea and A. alternata both in vitro and in vivo . The results showed that S. pararoseus ZMY-1 antagonized the three pathogens both in vitro and in apple fruit, and the antagonistic effect against P. expansum was the best. Considering commercializing S. pararoseus ZMY-1 as a potential biocontrol agent, three protective agents (skim milk powder, polyethylene glycol and trehalose) were added to make freeze-dried S. pararoseus ZMY-1. The appropriate cryoprotectant combination was optimized by a three-factor and three-level orthogonal experiment, which consisted of 1.5% skim milk powder, 0.1875% polyethylene glycol and 5.25% trehalose, and the survival of freeze-dried S. pararoseus ZMY-1 was improved to 93.9%. The freeze-dried yeast also showed good biocontrol efficacy against P. expansum , B. cinerea and A. alternata in apple fruit. Refrigerated storage at 4 °C was better than storage at 20 °C to maintain the stability of freeze-dried yeast, with higher survival of 66.5% after storage for 3 months. Therefore, freeze-dried marine yeast S. pararoseus ZMY-1 has good potential for biocontrol applications for postharvest fruit.