Extracellular ice nucleators (ECINs) were incorporated into foods and subjected to subzero freezing. Time-temperature profiles, ice-formation patterns and textures were examined by thermocouple, microscopy and texture analyzer. Onset temperatures (initial freezing), enthalpies and freezing rates were measured by DSC. Addition of ECINs to liquid foods elevated ice nucleation temperatures and promoted freezing. Solid or semisolid products frozen with ECINs resulted in a fiber-like texture. These effects were more apparent at Ϫ10°C or higher. Differential scanning calorimetry revealed onset temperatures were increased 11ЊC by addition of ECINs, but length of time to complete the phase transition was extended at constant cooling rates. Results indicated that ECINs can be used instead of whole bacterial cells for efficient freezing and textural modification.

Cells of ice‐nucleation active (INA) bacteria, Pseudomonas syringae and Erwinia herbicola, were cultured at 18°C with media of nutrient broth and/or yeast extract and harvested at late log phase for maximum ice nucleation activity. These cells were able to nucleate water to freeze at temperatures as high as −2°C. They were incorporated into model food systems, including sugar, protein solutions and oil/water suspensions, representing all major components of foods, to investigate their effects on freezing. The nucleation temperatures of all the treated models were significantly raised by between 3.0 and 5.9°C compared with controls when the freezer temperature was set at −6 to −7°C. The application of the INA cells also caused freezing of certain model solutions at −6°C, such as sucrose solution (10%), which did not freeze at the same conditions without INA bacterial cells. Additions of INA cells also shortened the total freezing time of the model systems by between 20 and 38%. These results suggest that with the application of bacterial ice nucleation, some current food freezing processes may be modified to operate at higher subzero temperatures to provide guaranteed freezing, energy savings and improvement of efficiency and product quality.

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