Analysis of Mass Transfer Process in Chinese Cabbage During Cooking With Consideration of Hindrance by Cuticle

Leafy vegetables have cuticle layers that hinder mass transfer. Although leafy vegetables are frequently heated with NaCl, the mass transfer difference between their cut and uncut surfaces during cooking remains uninvestigated. To simulate the NaCl concentration changes during the cooking of leafy vegetables, this study clarifies the difference between the mass transfer processes in cut and uncut surfaces of Chinese cabbage. The Chinese cabbage samples were soaked at 5-80°C and their inner and outer parts were separated. The diffusion coefficients (D) and mass transfer coefficients were determined using a three-dimensional diffusion equation. The NaCl concentration in the outer part with the cut surface rapidly increased compared with the inner part without the cut surface. The mass transfer coefficient used as a boundary condition was approximately 10^-11 times lower on the uncut surface (h_u) than that on the cut surface (h_c). D and h_u increased with increasing temperature, while h_c was not dependent on temperature. Results suggested that uncut surfaces hindered NaCl transfer during cooking. To validate the simulation of non-isothermal cooking, the samples were placed in a 1% NaCl aqueous solution at 100°C and heated for 10 min, after which they were maintained at 65°C for 120 min. The changes in NaCl concentrations in the aqueous solution and Chinese cabbage agreed well with the experimental values, validating the simultaneous simulations of NaCl concentrations in the aqueous solution and Chinese cabbage. Changes in the predicted NaCl concentration distribution visually revealed that NaCl diffused into Chinese cabbage mainly through the cut surface.