Developing Novel Micro Ohmic Cells: Evaluation of the Electrical Effect


Developing Novel Micro Ohmic Cells: Evaluation of the Electrical Effect

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To process food for safety, there is a need of microbial destruction rate. This was done traditionally using capillary tubes containing 0.1-0.2 ml of food matrix while knowing the heating time which is about 30 second to reach over 100°C from room temperature. Using advanced technologies such as Ohmic heating which is direct heating, dealing with such a small volume is not technically possible due to the need of metal electrodes inside the capillary tube to heat it up. Attempt has been made to make a small cell of about 2-3 ml to study the microbial inactivation but within the same heating rate as in case of capillary tubes. Therefore, food samples can be heat up as fast as using capillary tube although the volume is more.


Ohmic direct heating is considered to be green and efficient thermal processing with a potential of additional electrical effect compared with traditional methods. However, this additional non-thermal effect is not well explored in the literature. Variety of Ohmic units have been designed and reported but limited to either atmospheric pressure and/or too big for microbial inactivation, and mainly focusing on vegetative pathogens and not the bacterial spores (Cho et al., 1999, Shin et al., 2020, Müller et al., 2020).
Therefore, novel Ohmic cells of different sizes and configurations were designed and fabricated using Corning glass applicable to higher temperature under pressure. Developed micro Ohmic cell consists of a T-shape glass cell having volumes of 2 and 3 ml with two tiny Titanium electrodes mounted on Teflon caps tightly screwed on each sides. There is an opening section on top for feeding the cell while Fiber Optic sensors inserted for the evaluation of temperature uniformity and controlling process temperature located at the cold spot of the cell. Jacketed version of the cell was used to control the product temperature. Voltage gradients 90 and 135 V/cm were applied depending on the size of the cell resulting in very rapid Come-Up-Time (CUT) compatible with conventional capillary tubes. CUT reaching target temperature up to 121°C varied from 10 to 50 second depending on products properties and system parameters such as Proportional, Integral, and Derivative (PID) controlling loop. Temperature uniformity was confirmed with less than 1°C variation across the cell.
Exploratory studies revealed that the newly assessed micro Ohmic cell is promising for inactivation studies using different microorganism and food media where small volume, rapid CUT and uniform temperature are required. Variable voltage can be applied continuously using jacketed cell while the product temperature remains low-constant to study potential effect of the electrical field.

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