Postharvest Control of Gray Mold in Apples with Lyophilized Formulations of Cryptococcus laurentii: the Effect of Cold Stress in the Survival and Effectiveness of the Yeast

Cryptococcus laurentii BNM 0525 adapted to cold was used for developing a lyophilized formulation for controlling Botrytis cinerea (gray mold) in apples. For cold stress, the yeast was grown at 1 °C for 48 h. The trehalose content of stressed cells reached 109 mg g⁻¹ after 24 h, but it did not show significant modification in unstressed cells which were grown at 28 °C. The skimmed nonfat milk 10 %, yeast extract 0.5 %, and glucose 1 % (SMYG) medium was chosen as freeze-drying protectant for stressed and unstressed cells. After the freeze-dried process, stability of stressed yeast cells was significantly higher along 90 days of storage at 4 °C than that of unstressed cells. The effectiveness in protection against B. cinerea was also improved. When apple protection was performed with freeze-dried cells, the maximum protection was obtained with stressed cells. In this case, decay reduction percentage was 79.30 %, and there were no significant differences when a lyophilized formulation stored for 90 days was used. Unstressed cells were less effective immediately after the freeze-dried process (69.12 %) and less resistant to storage. The percentage of decay reduction was less to 60 % when applied with unstressed freeze-dried cells stored during 90 days. Cold stress increased the trehalose content in C. laurentii cells and improved the behavior of the yeast in front of preservation operations and also its effectiveness for controlling B. cinerea.