Effect of high-pressure treatments on microbial loads and physicochemical characteristics during refrigerated storage of raw milk Serra da Estrela cheese samples

This work studied the effect of high pressure processing (HPP) at 400, 500 and 600MPa during 10, 5 and 3min, respectively, on samples ewe cheese manufactured from raw milk, during storage (100days) at 5 degrees C. Total aerobic mesophilic and lactic acid bacteria were slightly affected, decreasing by about 1.0 and 0.82 log CFUg(-1), respectively, immediately after HPP treatment at 600MPa for 3min, while Enterobacteriaceae, yeasts and moulds, and Listeria innocua were reduced to below the quantification limits. Lactic acid bacteria decreased further during storage, showing increasing inactivation as the pressure level increased. Physicochemical parameters (water activity, moisture content, pH and titratable acidity) were generally not affected by HPP, while lipid oxidation increased throughout storage, with HPP samples showing lower values (50-66%) at 100days of storage. The results indicated that HPP has potential to improve cheese microbial safety and shelf-life, with a lower lipid oxidation level than nonpressurised cheese.