Effect of intracellular trehalose in Cryptococcus laurentii and exogenous lyoprotectants on its viability and biocontrol efficacy on Penicillium expansum in apple fruit

AIMS: To improve viability and biocontrol efficacy of Cryptococcus laurentii after freeze drying and in subsequent storage. METHODS AND RESULTS: Viability of C. laurentii was improved after freeze drying and in subsequent storage at 4 or 25 degrees C by using skimmed milk (SM) and sugars (glucose, galactose, sucrose and trehalose) as protectants. Sugars and SM mixed together showed better protection than when they were used separately. Citric acid used as carbon source could induce accumulation of intracellular trehalose in the yeast. The yeast cells with high trehalose level (HT cells) had higher viability than those with low trehalose level (LT cells) after freeze drying and storage for 90 days. After storage for 90 days at 4 degrees C, the HT cells plus SM and sugars as protectant showed a similar biocontrol effect against blue mould rot in apple fruit caused by Penicillium expansum as fresh cells. CONCLUSIONS: Increasing intracellular trehalose content of C. laurentii and adding exogenous protectant (sugars + SM) could improve its viability and maintain its biocontrol efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: The results have a potential value for commercial application of C. laurentii.