Experimental study and modelling of the ice crystal morphology of model standard ice cream. Part I: Direct characterization method and experimental data

A standard commercial dairy ice cream was used to study the ice crystal tex ture by a direct method namely by optical microscopy with episcopic coaxial lighting and with image analysis software (IPS). The exactness, precision and reproducibility of the method was checked. A mean ice crystal size at d ifferent locations inside the food samples was determined for different fre ezing conditions (initial temperature, freezing rate) and different composi tions with and without stabilizers. This relatively new method for foodstuf fs was compared with the freeze-drying method (indirect method) previously used in our laboratory and some discrepancies were observed. Because it pre served at best the frozen original texture, we think that this direct optic al microscopic method is more reliable and more precise than the other meth ods previously used. We observed that the mean crystal size increased with the distance to the cooling plate and, on the other hand, decreased with th e cooling rate or the cooling temperature. Due to its numerous advantages - i.e., low cost, rapidity, reliability and precision - we forecast, that th e use of this direct method, quite unknown to the frozen food technologist, will increase in the near future. (C) 2001 Elsevier Science Ltd. All right s reserved.