Effect of short time heating on the mechanical fracture and electrical impedance properties of spinach (Spinacia oleracea L.)

- Mechanical and electrical impedance properties of heated spinach were evaluated.
- An index for the non-uniformity of electrical properties of cells was defined.
- Cell structure was monitored by the equivalent circuit model analysis.
- Impedance properties were changed earlier and greater than those of fracture.
- Impedance properties can be an index for changes in fracture properties.

We evaluated the mechanical properties and electrical impedance data of spinach after short time heating. The mechanical fracture properties of samples heated for 40 s significantly differed from those of the non-treated samples. A circular arc of the Cole-Cole plot obtained from the impedance data shrunk after heating for 10 s. Similarity of the circular arcs, i.e. non-uniformity in the electrical characteristics, changed after heating for 30 s. After heating, extracellular resistance values were decreased from 650 to 16 kΩ, and cell membrane capacitance values were decreased from 13 to 0.28 nF. These changes could be evaluated simply by using the length of the coordinate at the top of the circular arc from the origin, and these occurred earlier and were greater in magnitude than those in the fracture properties were. These electrical properties could be an index for the early detection of changes in the fracture properties of samples.