[5-1130-P] Postharvest/Food Technology and Process Engineering (5th)

[5-1130-P-04] Effects of Heating under Pasteurization Conditions on Mechanical and Electrical Properties of Mung Bean Sprout

*Hayato Ogino¹, Haruki Ando¹, Satoshi Iwamoto¹, Teppei Imaizumi¹ (1. Gifu University(Japan))

Keywords:impedance, pasteurization condition, electrical property, mechanical property, mung bean sprout

Heat pasteurization using hot water is easy to introduce in small-scale facilities. However, heat treatments often degrade tissue structure and decrease texture of vegetables. Although cell membrane structure, which makes turgor pressure, is one of the most important factors to determine vegetable texture, heat-resisting properties of the structure is not well clarified yet. To date, impedance measurement has been used to evaluate cell membrane state. In this study, we mainly investigated such an electrical properties of mung bean sprout heated under pasteurization conditions, and evaluated relationships with its quality.Mung bean sprout is used in this study. A beaker containing 300 mL of distilled water was controlled at temperatures of 50, 60, 65 and 70 degree in a water bath. After measuring weight of mung bean sprout, it was put into a net and immersed in the beaker for 0 - 60 sec. Then, the sprout was immediately cooled in iced water for 30 sec. For the heated mung bean sprout, mechanical and electrical properties were measured. In order to measure the mechanical properties, a creepmeter (TPU-2D, Yamaden Co., Ltd.), equipped with a wedge-shaped plunger or a knife-shaped plunger, was used. The wedge-shaped and the knife-shaped ones were moved at 1 mm/sec for compression test and 10 mm/sec for shear test, respectively. For the impedance measurement, two needle electrodes (diameter: 0.25 mm) connected to a LCR tester (IM3536, HIOKI) were inserted into the sample. In this study, equivalent circuit analysis was conducted on the measured impedance values, and cell membrane capacitance, intracellular resistance and extracellular resistance were obtained. In addition, cell membrane structure was observed by using a confocal laser scanning microscope. In this study, two kinds of mechanical properties were evaluated for heated sprouts. While the compression force of the sample did not change a lot, significant differences were appeared on the shear force especially at 65 degree. In impedance measurement, measured values showed an arc when resistance and reactance were plotted on vertical and horizonal axis, respectively. Top coordinate of the arc decreased as the heating temperature risen. Additionally, an equivalent circuit model was well fitted to the measured values. The cell membrane capacitance decreased by the heating. Also, the extracellular resistance showed a decreasing tendency at heating above 60 degree. These changes seemed to relate with cell membrane damage which observed by the confocal laser scanning microscope. Consequently, our study indicated that impedance measurement was a good way to estimate texture and tissue structure of mung bean sprout. These findings will contribute to quality control of vegetables during heat processings.