Processing foods by high hydrostatic pressure.

摘要

HHP represents an attractive alternative to conventional thermal processing methods as no heat is required to inactivate vegetative forms of microorganisms thus, preserving the fresh attributes of foods. The applications of high hydrostatic pressure (HHP) in the food industry increased worldwide during the last decade.; This dissertation is organized in four chapters beginning with a review of HHP treatment in food preservation which explains the engineering principles of this technology and how HHP can be employed to inactivate microorganisms and modify the functional properties of food proteins.; The second chapter analyses the pressure dependence of thermodynamic and thermo-physical properties of water and foods. The specific volume, isobaric heat capacity, and volume expansivity of water are utilized to predict the temperature increase of compression of a water thermodynamic system. The values predicted are compared with temperature increase data measured during compression of foods with high moisture and lipid content. An energy balance was utilized to estimate the compression work required to pressurize a water system under adiabatic conditions to selected pressures. Potential applications of HHP technology in food freezing and thawing are reviewed and the thermodynamic data required to predict phase transitions under pressure are identified.; Chapter Three investigates the contribution of the come-up time (CUT) on the HHP inactivation of Escherichia coli and Listeria innocua inoculated in liquid whole milk. Longer CUTs resulted in higher inactivation of E. coli and L. innocua, as microbes were exposed to lethal pressures for longer periods of time. Although the use of short CUTs did not provide advantages in terms of inactivation efficiency in this particular case, short CUTs might be convenient in high pressure technology for reducing the total pressure cycle time which ultimately could reduce the processing costs.; Chapter Four analyzes the effect of selected pressures and pressure times on the coagulation properties of milk. Pressurizing milk to 655 MPa for the CUT decreases the rennet coagulation time, and increases the cheese yield by equivalent values than pressurizing milk to 310 MPa for 15 min. The former treatment could be advantageous in controlling undesirable microorganisms and plasmin activity.