Advantages of ohmic cooking in the kilohertz-range - part I: Impact of conductivity and frequency on the heating uniformity of potatoes

Abstract

The heating uniformity of potato cubes and whole potato tubers was investigated during cooking by ohmic heating (OH) in the low (12 kHz) and high (300 kHz) kHz range. Potatoes were heated in aqueous NaCl solutions with various conductivities (1–5 mS/cm). Conductivities and cell disintegration index of the tissue were determined in dependency of the temperature and the frequency at different points in the tubers. Heating uniformity was characterized by analyzing the temperature profiles with up to four thermocouples and by thermal imaging. Heating behavior of peeled and unpeeled tubers were compared to evaluate the impact of the skin on the OH treatment. For the higher frequency applied, increased electrical conductivities in the potato tissue were observed. At 300 kHz a better heating uniformity, with lower temperature differences within the potato samples compared to OH at 12 kHz was observed. The results provide a better understanding of the effect of high frequency electric fields on the heating uniformity and the conductivity of intact potato tissue. Industrial relevanceOhmic heating (OH) is an alternative heating technology with the potential to reduce processing times and energy consumption. It can overcome limitations in the heat transfer particularly given for large-volume solid foods and provide a uniform heating. However, limited attention has been given to the effects of the product and process parameters on the heating uniformity during OH treatments of solid foods. The present paper highlights the importance of the electrical conductivity and the frequency of the applied electric field on the heating uniformity. The obtained results contribute to the understanding of the interaction of the electric field and the food matrix, which is the basis for the implementation of tailored and targeted processing concepts in the industry.