FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY




Effect of high hydrostatic pressure on microorganisms present in milk and on milk properties


The technique of high hydrostatic pressures (UHP), an up-to-date technology of preserving and forming sensory characteristics of food, may be an alternative to heat treatment of many food products, including milk. The paper present the current state of knowledge as regards the effect of high hydrostatic pressure on micro -organisms contained in milk and on the major properties of milk. Vegetative forms of yeasts and moulds, and their spores are destroyed by a 200 to 400 MPa pressure, vegetative forms of bacteria (including pathogenic) by a 300 to 600 MPa pressure, while spores by a pressure higher than 1000 MPa. Viruses have very different resistance levels to pressure. High-pressure treatment that causes changes in mineral components of milk increases its pH. Casein micelles break down into small particles; this, in turn, reduces turbidity and clarity of milk, and increases its viscosity. Appropriately selected pressurization parameters affect technological properties of milk. The effect of pressure between 100 and 300 MPa is: enhancement of the rennet coagulation properties of milk and reduction in the coagulation and gelation time. When applying a pressure between 200 and 400 MPa, it is possible to obtain a harder coagulum. During acid coagulation, the application of high pressure increases the rate of acidification, which results in obtaining a coagulum of a higher firmness, strength, and resistance to syneresis.


micro-organisms, colour, viscosity, rennet coagulation, acid coagulation, pressurization