Tomato peeling by ohmic heating with lye-salt combinations: Effects of operational parameters on peeling time and skin diffusivity

• Ohmic heating in lye-salt solutions peels tomatoes.
• Peel cracking time is a function of solution composition and field strength.
• Lye diffusivity through tomato skin is greatly enhanced by an electric field.
• Tomato skin breakdown is greatly accelerated by an electric field.

Ohmic heating without lye has shown promise in tomato peeling; however the use of lye is known to yield high peeled-product quality. In this work, we studied the operational parameters of the ohmic peeling process, specifically, the influence of salt-lye concentration combinations and field strength on time for skin cracking during ohmic peeling. We further investigated the influence of electric fields on the lye diffusivity through tomato skin. The treatments of 0.01/0.5% NaCl/NaOH at 1610 V/m and 0.01/1.0% NaCl/NaOH at 1450 V/m were the conditions that required the shortest time for cracking. For NaCl/KOH mixtures, 0.01/0.5% NaCl/KOH at 2020 V/m and 0.01/1.0% NaCl/KOH at 1450 V/m required the shortest time for cracking. Studies on diffusion through the tomato skin showed that ohmic heating significantly improved lye diffusion (p < 0.05) at both 50 and 65 °C. After an initial period, diffusivities of lye peeling with ohmic heating were greater than those without ohmic heating at both 50 and 65 °C, confirming that the electric field enhances diffusion of NaOH through the tomato skin.