Environmental impact of novel thermal and non-thermal technologies in food processing
Introduction
Food preservation whilst ensuring its safety and quality has been a prime goal of food processors. The use of heat through thermal processing operations, which among others includes pasteurization, sterilization, drying and evaporation, is still a common practice of the food industries in order to guarantee the microbiological safety of their products. These traditional heating methods rely essentially on the generation of heat outside the product to be heated, by combustion of fuels or by an electric resistive heater, and its transference into the product through conduction and convection mechanisms. However, these ways of processing are still limited due to considerable losses of heat on the surfaces of the equipment and installations, reduction of heat transfer efficiency and thermal damage by overheating, due to the time required to conduct sufficient heat into the thermal centre of foods. Some of these effects are being attenuated through developments on control and monitoring systems for food processing plants, intelligent design of equipments and installations, heat recycling and isolation measures, but this also represents high additional financial costs. Therefore the efforts of processors together with academic circles in attending consumer demands for high quality food and dealing with raising economic standards, and nowadays particularly with ecological concerns, has triggered the development of emergent technological approaches for food processing. Recently, electromagnetic technologies in food processing have gained increased industrial interest and have potential to replace, at least partially, the traditional well-established preservation processes (Vicente & Castro, 2007). Ohmic heating and dielectric heating, which includes radio frequency (RF) and microwave (MW) heating, are promising alternatives to conventional methods of heat processing. These novel thermal technologies are regarded as volumetric forms of heating in which thermal energy is generated directly inside the food. This common pattern of heat generation allows overcoming excessive cooking times and consequently may have direct implications in terms of both energetic and heating efficiency. In the last decade, non-thermal technologies for inactivating microorganisms have also been developed in response to the worldwide interest for more fresh and natural food products. Novel non-thermal technologies such as ultrasounds (US), high pressure processing (HPP) pulsed electric fields (PEF) and pulsed light treatment (PL), among others, have the ability to inactivate microorganisms at near-ambient temperatures, avoiding thermal degradation of the food components, and consequently preserving the sensory and nutritional quality of the fresh-like food products. Some of the effects of these novel thermal and non-thermal technologies on the preservation and quality of several food products have been reviewed and constitute valuable information for regulatory approval and as backup for investment decisions from food processors. In order to achieve their full potential for industrial implementation and commercial exploitation, issues related with the environmental impact, such as e.g. wastewater and gas emissions, the conservation of non-renewable resources and energy consumption are increasingly attracting the attention of the food processors since they can represent significant reductions of the processing costs. The purpose of this text is to provide a general perspective of the so-called novel thermal and non-thermal processing technologies currently available in connection with their actual and foreseen environmental impact once implemented by the food industry.
Section snippets
Radio frequency (RF) and microwave (MW) heating
Dielectric heating implies the interaction between an electromagnetic alternating field and the dipoles and ionic charges contained within a food product that enables the volumetric heating of the product. RF and MW systems operate by the same principle, forcing polar molecules, such as water, and ionic species to constantly realign themselves by reversing an electric field around the food product. This molecular movement is extremely fast due to the high frequency of the field, which in RF can
Novel non-thermal processing technologies
The term ‘non-thermal processing’ is often used to designate technologies that are effective at ambient or sublethal temperatures. High hydrostatic pressure, pulsed electric fields, high-intensity ultrasound, ultraviolet light, pulsed light, ionizing radiation and oscillating magnetic fields have the ability to inactivate microorganisms to varying degrees (Butz & Tauscher, 2002). Some of these treatments may involve heat due to the generation of internal energy (e.g. adiabatic heating and
Environmental impact
The energy consumption and energy savings in the food industry have been in focus for the last 30 years. This is due in part to comprehensive automation of production processes and particularly by the increasing demand for food safety. The higher levels of hygiene consecutively established as goals subsequently lead to a larger consumption of cold and hot water as well as an increased number of cleaning cycles in production (Dalsgaard & Abbots, 2003). This has dramatically increased the
Conclusions
The application of emerging thermal and non-thermal technologies holds potential for producing high-quality and safe food products. Current limitations, related with high investment costs, full control of variables associated with the process operation and lack of regulatory approval have been delaying a wider implementation of these technologies at the industrial scale. It is likely that some of these technologies, according to their specificities, will find niche applications in the food
Acknowledgement
Author is thankful to the Fundação para a Ciência e Tecnologia (FCT, Portugal) for its Doctoral grant.
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