Opinion on the use of ohmic heating for the treatment of foods

Abstract

BackgroundThe working group “Food Technology and Safety” of the DFG Senate Commission on Food Safety (SKLM) deals with new technologies which are being developed or used to treat foods. Ohmic heating is a new process for heating food by means of direct application of current to the food. Compared to conventional heating methods, this process can achieve shorter heating times while avoiding hot surfaces and can reduce temperature gradients. The electrical, thermophysical and rheological properties of the products play an important role in achieving uniform heating. In addition to the product parameters, process parameters such as the current frequency used, the electrode material and the geometry of the treatment chamber are also relevant. Scope and approachOn June 22nd 2015, the SKLM issued an assessment of the process for Ohmic heating of food in German. The English version was issued on December 14th, 2015. The objective of this statement was to describe the state of the research, to draw attention to critical points in the application and science-based further development of the process, and to define the need for research. Key findings and conclusionsAs with conventional heating, the effectiveness of ohmic heating as a preservation process depends on reaching and maintaining a certain temperature at each point of the food for a sufficient period of time to inactivate microorganisms. The physicochemical product properties are extremely important for achieving heating conditions that are as uniform as possible. Because the electric field strengths applied are low, mainly thermal effects come into play. However, some studies discuss potential additional synergistic or non-thermal inactivation effects of the electric field. As with other processing methods, the structure and concentration of ingredients and contaminants in foods may be altered during ohmic heating. Besides the thermal effects of ohmic heating, it is also necessary to pay attention to potential electrochemical reactions at the contact surface between electrodes and food as well as potential non-thermal effects of the electric field, depending on the process conditions. Therefore, process control becomes particularly important to prevent such effects, which are sometimes undesirable.Compared to conventional heating methods, the primary requirement in evaluating ohmic heating is a standardised means of acquiring the process control parameters. This includes, first and foremost, a space- and time-resolved temperature measurement that takes into account the product and electric field properties. It is absolutely necessary to carry out systematic studies while paying attention to the comparability with respect to product and process parameters as well as the system design. Consequently, the existing gaps in the data records are in part due to the insufficient comparability of the available studies.Moreover, it is necessary to analyze thermal and non-thermal as well as additional process-induced changes in the food and its ingredients. This applies particularly to the effect on the potential allergenicity of the food components.Thermal and non-thermal effects can be studied in a differentiated manner in simulation models. This is regarded as a promising approach for providing a model-like description of combination processes and for optimising process conditions as well.