| The aim of this research was to study the influence of biogenic ice nucleators on freezing characteristics of a food simulant for beef (Tylose), using sample dimensions, representative of commercially frozen foods. Specific attention in this study was given to effects on freezing time, local freezing rates, nucleation temperature, fraction of frozen water, ice crystal sizes, and distribution of crystal sizes throughout the product. Application of bacterial ice nucleators (INA+ E. coli M15) led to an increase (+/-4°C) in the nucleation temperature on the surface of large (10 cm diameter sphere), medium (5 cm sphere), and small (+/-1.5 gram Tylose in test tube) samples of Tylose. The smaller Tylose samples generally supercooled more uniformly and to lower temperatures than larger samples. Substantial reductions (17.2%) in freezing time were only observed, when nucleators were added to small Tylose samples (+/-1.5 gram) frozen at -10°C.; A method for visualizing and quantifying ice crystal sizes (and distribution) throughout Tylose samples was developed and validated. Spherical samples of Tylose revealed small crystals near the center, whereas larger crystals were observed near the surface. Crystals size measurements in small, medium and large samples were quantitatively related to local freezing rates. Under the freezing conditions studied, bacterial ice nucleators only had an effect in medium samples, creating a more uniform distribution in freezing rates and crystal sizes.; The freezing process, including supercooling, fraction of frozen water, and effect of bacterial ice nucleators was simulated by constructing and employing a numerical freezing model. A close agreement (<+/-7% difference) was found between simulation and experimental findings. The incorporation of a prediction of the local change in fraction of frozen water as a function of time provided a clear illustration of the effect of supercooling on the rate of ice formation at various positions.; Parametric analysis was performed on the simulation to investigate the effect of manipulation of supercooling (e.g. by ice nucleators) under various hypothetical freezing conditions. These results suggested that most interesting applications (e.g. uniform and rapid ice formation) for the food industry may be found in promoting, rather than eliminating supercooling. |
