ABSTRACT
During the last 25 years, consumer demands for more convenient and varied milk food products, together with the need for faster production rates, improved quality, and extension in shelf life have brought significant improvements to the processing of fluid milk and milk products. Many technological developments have been directed toward unit operations such as separation, standardization, pasteurization, and packaging, leading to considerable advances in mechanization, automation, energy efficiency, hygiene, and quality within the processing plant (Goff and Griffiths 2006). In particular, extending the shelf life of milk and milk products without compromising their quality and safety has been a prime goal of milk processors. In general, the use of heat is still
7.1 Introduction .................................................................................................. 155 7.2 Thermal Processing ...................................................................................... 156 7.3 Novel Thermal Processing Technologies ..................................................... 157
7.3.1 Ohmic Heating (OH) Technology..................................................... 157 7.3.1.1 Microbial Inactivation ........................................................ 160 7.3.1.2 Enzyme Inactivation .......................................................... 161 7.3.1.3 Effects on Physical-Chemical Properties .......................... 161
7.3.2 Microwave (MW) Heating ............................................................... 162 7.3.2.1 Potential Effects ................................................................. 163 7.3.2.2 MW and Microorganisms .................................................. 163
7.3.3 Infrared Heating (IH) ....................................................................... 164 7.4 Novel Nonthermal Processing Technologies ................................................ 165
7.4.1 Pulsed Electric Field (PEF) .............................................................. 165 7.4.1.1 Inactivation Studies ............................................................ 166 7.4.1.2 Effects of PEF on Milk Quality ......................................... 167 7.4.1.3 Current Limitations ........................................................... 167
7.4.2 High-Pressure Processing ................................................................. 168 7.5 Final Remarks-The Hurdle Concept .......................................................... 169 References .............................................................................................................. 169
a common practice of the dairy industries in order to guarantee the microbiological safety of milk and its subproducts. However, the processing of milk through heating has had a noticeable evolution during the twentieth century, which has continued until the present time. The technological improvements together with the efforts and diligence of processors, technologists, and dairy researchers in bringing superior quality products to consumers, has been triggering the investigation and development of new technological approaches for milk processing capable of substituting the traditional well-established preservation processes. Thermal technologies such as ohmic heating, dielectric heating, and inductive heating have been developed and can replace, at least partially, the traditional heating methods that rely essentially on conductive, convective, and radiative heat transfer. Nonthermal approaches to milk processing, such as pulsed electric fields, high pressure, among others, may also be valuable alternatives to thermal processing, because they have the ability to inactivate microorganisms at near-ambient temperatures, avoiding the undesirable effects of heat on the organoleptic properties of foods. The purpose of this chapter is to provide a general perspective of the main thermal processing technologies currently available and, in particular, to give the reader an overview of the novel thermal and nonthermal processing technologies of fluid milk, while providing examples of recently conducted research.
