The use of soaking and blanching pre-treatments to improve Ohmic heating uniformity of beans–liquid mixtures

In this work cannellini beans were pre-treated by either blanching or soaking in salt solutions with the aim to improve the ohmic heating uniformity of beans-liquid mixture. Dry beans were pretreated by either soaking (12 h) in sodium chloride solutions of different concentration (0, 0.3, 0.5, 0.7, 1 and 1.5 g/100mL) or blanched for different length of times (35 and 50 s) in a water bath set at 90°C after soaking (12 h) in tap water. Heating curves of solid-liquid mixtures of different pre-treated beans to salt solution (1 g/100mL) ratio (60g of beans/100g of mixture and 53g of beans/100g of mixture) were determined in a static ohmic heating device by applying a constant voltage of 100V. Results showed that the ohmic heating rate of beans increased with increasing the salt concentration of the soaking solution as well as the blanching time as a direct result of the increase of electrical conductivity. The higher was the solid-liquid ratio, the greater was the heating rate of solid phase. Optimal pre-treatment conditions, which allowed the ohmic heating of both phases of solid-liquid mixture at comparable rate, were found when beans were pre-treated either by soaking in solutions with salt concentration of either 0.5 g/100mL (60g of beans/100g of mixture) or 1.5 g/100mL (53g of beans/100g of mixture), or when blanched for 50 s at 90°C (53g of beans/100g of mixture).