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

Abstract

Hachana, Y. and Kraïem, K. 2009. Proteolysis and storage stability of ultra high temperature processed milk as influenced by somatic cell count and bacterial count. J. Appl. Anim. Res., 36: 65–70.

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 (>2×10⁶ cfu ml⁻¹). It was concluded that initial somatic cell and bacterial counts of UHT milk determined its keeping quality.

Keywords:

• Somatic cell count
• bacterial count
• proteolysis
• organoleptic quality
• UHT milk