Relationship between casein micelle size, protein composition and stability of UHT milk

Abstract Casein (CN) micelle size has been suggested as important for stability of ultra-high temperature (UHT) treated milk. Therefore, full fat milk samples were pooled according to native CN micelle size (small, intermediate and large CN micelles), homogenised and UHT treated, and stored at 20 °C or 40 °C for up to 6 months to study storage stability. Small average CN micelle size was associated with higher relative content of κ-CN B and glycosylated κ-CN. Processing increased particle size in the skimmed milk, resulting in comparable sizes, regardless of initial size. Major changes in physicochemical properties were observed for all milk pools directly after processing and during storage, greater at elevated storage temperature. Interestingly, milk with small CN micelles before processing displayed significantly less formation of sediment during storage compared with milk with intermediate or large CN micelles, suggesting that inherent variation in milk quality is important for UHT milk stability.