Fat globule size distribution in commercial ice cream determined through ideal application of the laser diffraction technique

• Incorrect choice of extinction coefficient can result in a specious mode • Some ice cream has a previously unreported third mode • Dispersion of samples in simulated milk ultrafiltrate does not improve results Design of systems for recovering fat from waste ice cream requires knowledge of the fat globule size distribution. Laser diffraction has often been used to measure this distribution, but it has almost always been done using laboratory-made ice cream. Past reports very often contain indications of serious methodological flaws. This study demonstrates a careful selection of analysis parameters and methodology choices, in order to prevent known sources of error in particle size distribution (PSD) results, and to use the laser diffraction instrument to its best advantage. It is shown that data quality degrades when either laser obscuration or measurement duration are outside of narrow ranges. Additionally, a value given in the literature as a recommendation for extinction coefficient may be wrong by a factor of 100. Using the methodology developed in the present study, 26 varieties of commercial vanilla ice cream were analyzed for their PSD. A small size mode, sometimes reported in the literature and attributed to free casein micelles, was absent from the PSD of all ice cream varieties; dispersion of samples in simulated milk ultrafiltrate did not meaningfully impact these results. Further, a large size mode, rarely reported in the literature, was found in about half of the ice cream varieties tested. Overall, the results demonstrate that the laser diffraction technique must be used with care, and that understanding of nature of the sample material is crucial.