Preparation of a Composite Freeze‐Dried Microorganisms Agent for Controlling Postharvest Pathogens in Table Grapes

Currently, biological control technologies are highly favored for their environmental friendliness and high safety profile. Among these, antagonistic yeasts and antagonistic bacteria are applied to control postharvest diseases in fruits and vegetables due to their outstanding efficacy. This study combined two antagonistic yeasts, Rhodotorula graminis and R. babjevae with two antagonistic bacteria, Bacillus licheniformis and B. velezensis into a composite formulation. Using freeze‐drying technology, the mixture was processed into a solid preparation, and its efficacy in controlling postharvest diseases in grapes was investigated. Results indicate that through single‐factor and response surface optimization experiments, the optimal protective agent formulations for each antagonistic microorganism were determined. For R. graminis (skimmed milk powder 5 g/100 mL, glycerin 4 g/100 mL, trehalose 2.5 g/100 mL) and for R. babjevae (skimmed milk powder 5 g/100 mL, glycerin 4 g/100 mL, trehalose 10 g/100 mL). The optimal protective concentration for B. licheniformis and B. velezensis was 3 g/100 mL yeast extract. Meanwhile, this composite freeze‐dried antagonistic microorganism agents continued to significantly reduce the incidence of rot caused by Penicillium expansum and Aspergillus niger in grape fruits even on the 90 th day of storage.