Improvement of the cryopreservation of the fungal starter Geotrichum candidum by artificial nucleation and temperature downshift control

Food industry tends towards the use of controlled microorganisms in order to improve its technologies including frozen starter production. The fungus Geotrichum candidum, which is currently found in various environments, is widely used as ripening agent in some specific cheese making process. In order to optimize the cryopreservation of this microorganism, freezing experiments were carried out using a Peltier cooler–heater incubator, which permits to control the temperature downshift from +20 to −10 °C in time period ranges from 20 to 40 min depending on the experiments. Concomitantly, study of the effect of an industrial ice nucleator protein derived from Pseudomonas syringae (SNOMAX®) on the dynamic of freezing of G. candidum was carried out. Our results showed that the addition of this protein in the microbiological suspension has different complementary effects: (i) the synchronization of the different samples nucleation, leading to an homogeneous and earlier freezing, (ii) the increase of the freezing point temperature from −8.6 to −2.6 °C, (iii) a significant decrease of the lethality of G. candidum cells subjected to a freezing–thawing cycles challenge.