Effect of ultra high-pressure homogenisation on natural-occurring micro-organisms in bovine milk

This study aimed to evaluate the effect of ultra high-pressure homogenisation (UHPH) on natural-occurring micro-organisms in bovine milk. Whole raw milk was standardised at 3.5% and was processed using a Stansted High Pressure Homogeniser (model FPG11300, Stansted Fluid Power Ltd., Essex, UK). The microbiological quality of raw, high pasteurized (90°C, 15 s) and pressure treated (200 and 300 MPa at inlet temperatures of 30 and 40°C) milks was studied by enumerating total bacteria, psychrotrophic bacteria, coliforms, lactococci, lactobacilli and enterococci. UHPH treatments were as efficient (99.99%) as high-pasteurization treatment in reducing the total bacterial population, reaching important reductions (3-4 log cfu/ml). Lactococci count behaviour was similar to that of total bacteria count, reaching the same reductions. Psychrotrophic bacteria counts were not detected in high-pasteurized milks and were reduced by 3-4 logs and on some occasions up to undetected levels in UHPH-treated milks. Coliforms, lactobacilli and enterococci were completed destroyed by both UHPH and heat treatments.