Addition of ice-nucleation active bacteria: Pseudomonas syringae pv. panici on freezing of solid model food

Ice-nucleation active bacteria (INAB), Pseudomonas syringae pv. panici, were cultured at 26 °C in a nutrient broth and harvested at late log phase. The ice-nucleation activity unit per unit volume of the bacterial culture measured by the droplet-freezing assay developed by Vali was 3.29 × 104 INA/mL. A differential scanning calorimetry (DSC) analysis of 77 g/100 g Tylose samples showed that the addition of bacteria had no obvious effect on the glass transition temperature and heat of fusion of the samples. Freezing operations carried out at −20 °C showed that the addition of INAB produced no obvious change in the freezing time. The scanning electronic microscope (SEM) observation of microstructure of the model food indicated that the mean ice crystal size was reduced from 25.7 μm to approximately 15 μm by the addition of INAB.