EFFECTS OF ICE-NUCLEATION ACTIVE BACTERIA ON THE FREEZING OF SOME MODEL FOOD SYSTEMS

Cells of ice-nucleation active (INA) bacteria, Pseudomonas syringae an d Erwinia herbicola, were cultured at 18 degrees C with media of nutri ent broth and/or yeast extract and harvested at late log phase for max imum ice nucleation activity. These cells were able to nucleate water to freeze at temperatures as high as -2 degrees C. They were incorpora ted into model food systems, including sugar, protein solutions and oi l/water suspensions, representing all major components of foods, to in vestigate their effects on freezing. The nucleation temperatures of al l the treated models were significantly raised by between 3.0 and 5.9 degrees C compared with controls when the freezer temperature was set at -6 to -7 degrees C. The application of the INA cells also caused fr eezing of certain model solutions at -6 degrees C, such as sucrose sol ution (10%), which did not freeze at the same conditions without INA b acterial cells. Additions of INA cells also shortened the total freezi ng time of the model systems by between 20 and 38%. These results sugg est that with the application of bacterial ice nucleation, some curren t food freezing processes may be modified to operate at higher subzero temperatures to provide guaranteed freezing, energy savings and impro vement of efficiency and product quality.