Proteolysis and Storage Stability of Ultra High Temperature Processed Milk as Influenced by Somatic Cell Count and Bacterial Count

To study keeping quality of UHT processed 1.5% fat milk of different somatic cell count (SCC) and bacterial count (BC), that would be sufficient to produce an off-flavor, a 180 days experiment was conducted. Sixty eight per cent of panelists detected off-flavor related to proteolysis, when the decrease in casein as a percentage of true protein (CN/TP) was > 5%. UHT milk produced from low SCC milk (50,000 cells ml⁻¹) and low bacterial count (<10⁵ cfu ml⁻¹) maintained high organoleptic quality for the entire 180 days shelf-life period. UHT milk produced from milk with high SCC (740,000 and 1,102,000 cells ml⁻¹) developed an off-flavor at about 90 and 60 days, respectively. Off-flavor was detected at 30 days storage when BC was high in raw milk (>2x10⁶ cfu ml⁻¹). It was concluded that initial somatic cell and bacterial counts of UHT milk determined its keeping quality.