Electrical Conductivity of Yellowtail (Seriola quinqueradiata) Fillets During Ohmic Heating

Abstract

Electrical conductivities (ECs) of ordinary (white) and dark (red) muscles of yellowtail (Seriola quinqueradiata) fillets were measured at frequencies between 50 and 20,000 Hz from 15 to 80 °C to provide insights into improving the modeling of continuous ohmic heating (OH) in fish products. The effects of temperature, muscle types (ordinary and dark), muscle composition (moisture and fat content), muscle and current direction (parallel and series), and muscle membrane on EC were investigated during OH. At 20 kHz, the ECs of yellowtail fillets increased linearly with increasing temperature (p < 0.01). Compared with the dark muscle (moisture content 60.4 ± 1.6 %, fat content 18.7 ± 2.1 %), the ordinary muscle (moisture content 63.5 ± 1.0 %, fat content 7.3 ± 0.9 %) has a high EC value. The parallel type (direction of current in fish) of yellowtail fillets has a higher EC value than the series type. The EC of the minced yellowtail is in between the value of the two types of muscles. Temperature, fat and moisture contents, and current direction all influenced the EC, and especially the muscle membrane connecting fiber has a major influence on EC of two different types of muscles. The thickness and EC of muscle membrane were measured and calculated using magnetic resonance imaging and simultaneous equations, respectively. The calculated values were compared with the experimental values; the correlation coefficients of all samples were above 0.99, and the relative root mean square error and maximum relative error values demonstrated that both values are in good agreement.