Potential application of electrical conductivity measurement for freshness assessment of tofu

The potential of using electrical conductivity measurements to evaluate the freshness of tofu during storage was studied. Changes in the electrical conductivity of tofu were measured using a custom system under refrigerated (5 °C) and room temperature conditions (20 °C). The electrical conductivity of tofu stored at room temperature rapidly increased from 0.46 to 0.81 S/m within 9 days. During refrigerated storage, the conductivity slowly increased from 0.30 to 0.41 S/m over 24 days. The electrical conductivity data were converted into an electrical conductivity freshness index (EF_i) to develop an empirical model for physicochemical qualities (pH and texture) and microbial growth. In the pH analysis, EF_i could well predicted the pH reduction following spoilage during both refrigerated and room-temperature storage. For example, the EF_i empirical model showed ß₂ coefficient and R² values of − 2.553 and 0.976, respectively, for pH estimation of refrigerated tofu. Microbial growth could be precisely predicted using electrical conductivity measurements since the empirical parameter of EF_i showed positive values. The results of this study suggest that in situ electrical conductivity measurements can be used for the rapid estimation of tofu freshness during storage.