Production of an 18% protein liquid micellar casein concentrate with a long refrigerated shelf life

Our objective was to develop a process to produce a high-concentration liquid micellar casein concentrate (18% protein, MCC18) with a long refrigerated shelf life. The MCC18 is a novel milk protein ingredient produced by fractionating skim milk using microfiltration (MF). To achieve a long refrigerated shelf life, the processing of MCC18 was designed to maximize the removal of low-molecular weight compounds [e.g., lactose and nonprotein nitrogen (NPN)] that can be easily metabolized by microbes, while minimizing the microbial count in the final product. The production of MCC18 was done over a period of 5 d. The experiment was replicated 3 times in different weeks with a different batch of raw milk. Raw whole milk was pasteurized and separated to produce skim milk. Skim milk was ultrafiltered (UF) to remove more than half of the lactose and NPN. The UF milk retentate was diluted with water and then MF in 3 stages to remove approximately 95% of the serum protein and further remove lactose and NPN. The retentate from the last stage of MF was UF to concentrate the protein to 18% and batch pasteurized. The MCC18 was collected immediately after processing in sterile plastic vials and stored at 4°C. The average MCC18 contained 21.78% total solids, 18.27% true protein, 0.31% NPN, and 0.13% lactose. The MCC18 at the day of processing contained a mean aerobic bacterial count of 2.1 log cfu/mL and mean aerobic spore count of 2.3logcfu/mL. The MCC18 formed a solid gel at temperatures <22°C, but the MCC18 reverted back to a liquid when warmed from 4°C temperature to >22°C. This provides a unique opportunity in ingredient handling and packaging and eliminates the challenges encountered in reconstitution of dried milk protein ingredients. The MCC18 produced in this study maintained a bacteria count <20,000 cfu/mL for 16wk when stored at a refrigeration temperature of 4°C. Further study is needed to determine if changes occur in the organoleptic and functional properties of MCC18. We envision that the conversion of skim milk to MCC and its coproducts (serum protein concentrate and lactose concentrate) could be used as an alternative to the production of nonfat dry milk to balance milk production seasonality, specifically the components of skim milk portion.