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

Abstract

A standard commercial dairy ice cream was used to study the ice crystal texture 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 different locations inside the food samples was determined for different freezing conditions (initial temperature, freezing rate) and different compositions with and without stabilizers. This relatively new method for foodstuffs was compared with the freeze-drying method (indirect method) previously used in our laboratory and some discrepancies were observed. Because it preserved at best the frozen original texture, we think that this direct optical microscopic method is more reliable and more precise than the other methods previously used. We observed that the mean crystal size increased with the distance to the cooling plate and, on the other hand, decreased with the cooling rate or the cooling temperature. Due to its numerous advantages – i.e., low cost, rapidity, reliability and precision – we forecast, that the use of this direct method, quite unknown to the frozen food technologist, will increase in the near future.