Construction of Composite Biocontrol Agent (BCA): Developing Effective Strategies for Controlling Postharvest Blue Mold and Patulin in Apples

Postharvest blue mold in apples, caused by <i>Penicillium expansum</i>, leads to fruit decay and patulin (PAT) contamination, incurring major economic and health risks. This study developed a composite biocontrol agent (BCA) by co-cultivating three antagonistic yeasts (<i>Meyerozyma caribbica</i>, <i>Metschnikowia zizyphicola</i>, and <i>Pichia rarassimilans</i>). Mixed-culture conditions and protective additives formulation were optimized via response surface methodology. Optimal biomass production was achieved with a 1:2:3 (<i>v</i>/<i>v</i>/<i>v</i>) yeast ratio in medium containing sucrose (12.49 g/L), yeast extract powder (13.3 g/L), K₂HPO₄ (0.88 g/L), and NaCl (0.95 g/L) under pH 7.0, 1% total inoculum concentration, 24 °C, and a 60 h incubation. The liquid BCA formulation, stabilized with 0.27% gum arabic, 0.49% Tween-80, and 0.079% ascorbic acid, maintained high viability (9.15 log10 CFU/mL after 7 days). In vivo/in vitro trials all demonstrated that the composite BCA rapidly colonized, suppressed <i>P. expansum</i> infection, and significantly delayed pathogen spore germination and hyphal growth. Furthermore, the BCA effectively degraded 10 μg/mL PAT within 24-42 h in various fruit juices with minimal adverse effects on juice quality parameters. Storage at -20 °C preserved the highest bioactivity (7.93 × 10⁸ CFU/mL after 5 months). This optimized composite yeast formulation provides an efficient, eco-friendly strategy for integrated apple postharvest blue mold and PAT detoxification.