Effect of Freezing on Electrical and Rheological Properties of Food Materials

Abstract

Changes in electrical and rheological properties in freezing-thawing were measured and compared for various food materials, which could be classified into three groups. In the first group, plant tissue (vegetables and fruits) showed large and frequency-dependent impedance and clear characteristic Cole-Cole arc in their fresh state. These electrical properties drastically changed after freezing-thawing: impedance greatly decreased and the Cole-Cole arc disappeared, suggesting the serious change in the cell structure. Correspondingly, the dynamic elasticity and viscosity substantially decreased. In the second group, animal and fish meats showed the lower impedance and unclear Cole-Cole arc as compared with plant tissue, but these properties scarcely changed after freezing-thawing. Rheological properties were also unchanged reflecting the large freezing-tolerance for food materials in this group. In the third group, konnyaku (alimentary yam paste) and tofu (soyprotein curd) showed increase both in impedance and viscoelasticity after freezing-thawing reflecting the freezedenaturation of the major components.

Computational Simulation and Developments Applied to Food Thermal Processing

“…The accuracy obtained may allow this approach to be used as a guideline for freezing experiments, freezing equipment design, and frozen food production [39]. Similar results, as well as freezing time and temperature distributions, have been reported by Zhao et al [58], Ohnishi et al [60], Haiying et al [61], Delgado and Rubiolo [48] and Li et al [62] for fish, vegetables, and beef samples, by applying different analytical and numerical methods to predict freezing times, freezing temperatures, and final product quality.…”

Ohmic Heating of Peaches in the Wide Range of Frequencies (50 Hz to 1 MHz)

“…Usually, to minimize undesirable electrochemical reactions between electrodes and food product, an increase in the alternating electric field frequency is required (Amatore and others 1998; Samaranayake and Sastry 2005; Samaranayake and others 2005). Such an increase leads to a tissue electrical impedance decrease (Shaw and Galvin 1949; Ohnishi and others 2004). On the other hand, the electroporation process of plant tissue cell membranes was reported to be more pronounced at low frequencies (Mehrle and others 1990; De Vito and others 2008; Kulshrestha and Sastry 2003).…”

Effect of Freezing/Thawing Temperature on the Viscoelastic and Nutritional Qualities of Carrots

“…Freezing/thawing processes can decrease the elastic properties of vegetables by one or two orders of magnitude. [12] To our knowledge, the comparison of viscoelastic behaviors of vegetables at different freezing/thawing conditions has not been investigated. Monitoring their detailed information could be in favor of providing an optimum condition and a maximum product quality.…”