Food processing by nonthermal technologies

In recent years consumers have become more concerned about the processed foods they buy and eat. Consumers demand food products that are safe, nutritious and of good quality. This demand resulted in researchers from industry and from academia looking for new processing technologies that better preserve food attributes. This dissertation includes research on three nonthermal technologies: pulsed magnetic fields, ultra high pressure and pulsed electric fields available at the Center for Nonthermal Processing of Foods at Washington State University. Chapters One, Two and Three include reviews on the mode of action and degree of development of pulsed magnetic fields, ultra high pressure and pulsed electric fields technologies, respectively. Chapters Four and Five include basic research on microbial inactivation by static and pulsed magnetic fields, and show that, at present, magnetic fields technology is not suitable for microbial inactivation nor food preservation. Chapter Six includes research on the high pressure processing of milk prior to Cheddar cheese making and shows how yield, composition and rheological characteristics of Cheddar cheese are affected depending on the applied pressure. Ultra high pressure treatment of raw milk increased wet yield up to 8% when 676 MPa were applied. On the other hand, cheese rheology was only affected when protein incorporation did not involve greater moisture retention. Although currently used in the food industry for processing of specific products, the potential for using ultra high pressure in the production of dairy products is demonstrated. Finally, Chapter Seven compares and evaluates the suitability of different models to describe the inactivation kinetics of Listeria innocua by pulsed electric fields and demonstrates that a statistical approach provides a better description of survival curves than the traditional single target theory widely used in thermobacteriology. Understanding microbial inactivation kinetics is required prior to industrial scale-up of pulsed electric fields technology. Finally, while the application of magnetic fields for microbial inactivation is not foreseen in the near future, the use of pulsed electric fields for food processing has great potential for being industrially implemented, whereas for ultra high pressure processing a successful expansion towards the dairy industry should be expected.