Invited review: Uncovering fraudulent addition of reconstituted milk in liquid bovine milk—A critical review of analytical techniques

This review provides an overview of analytical techniques that have been published for detecting the (fraudulent) addition of reconstituted bovine milk to liquid bovine milk and identifies which of these techniques are most suitable for identifying partial replacement of liquid bovine milk by reconstituted bovine milk at levels that are economically meaningful. Evaluation of these analytical techniques was done against a detection limit of 10% inclusion of reconstituted milk. In total, 30 studies were included and categorized to deal with type II heat indicators, spectroscopic techniques, omics techniques and other techniques, respectively. The variation in the lowest detectable level of added reconstituted milk powder to liquid milk is very high, ranging from 0.5 to 50%, highly depending on the fat content and temperature treatment of both reconstituted milk and liquid milk. In cases that liquid milk and reconstituted milk with similar fat content and comparable processing histories are combined, the sensitivity of most techniques decreases. In many cases the sensitivity even may be insufficient to reliably identify adulteration at economically relevant levels. Many recent publications describe omics-based techniques which show high potential for detecting fraudulent addition of reconstituted milk in liquid milk, even though these techniques in many cases need further exploration of their potential by applying the techniques to a sample set reflecting the typical adulteration practices. In conclusion, the detection of fraudulent addition of reconstituted bovine milk in bovine liquid milk remains challenging and relevant up to today.