Mass transfer phenomena for erythrosine and red gardenia dyes in cherries (Prunus avium) : influence of temperature on effective diffusion coefficients

Abstract

The study focuses on the quantification of the diffusion phenomenon of the artificial and natural colourant, erythrosine, and red gardenia, respectively, at 238 ppm and different temperatures (40, 50 and 60°C) in cherries, by means of the calculation of diffusion coefficients, using a mathematical model based on Fick's second law. CIELAB colour space parameters were measured in triplicate, with a Konica Minolta CR-400 colourimeter device, D65 illuminant, in approximately 5 kilograms of calibrated, pitted, and desulfited cherries for 24 h, through immersion in water baths, prior to the candying process. The sampling of cherries was carried out at different frequencies, whilst as the phenomenon of colouration progressed, two cherries were randomly extracted from different parts of the container to dispose cross section and measure the colour space parameters, thus detecting colour changes during pigment diffusion. Additionally, effective diffusion coefficients in skin and flesh were calculated, adjusting a hollow sphere diffusion model to experimental values. A significant difference was observed in red gardenia effective diffusion coefficients (p<0.05), contrary to those calculated for erythrosine (p>0.05), this might indicate that diffusion of red gardenia between temperatures is differential. Superior coefficients were obtained according as the temperature increased, indicating that this could accelerate the diffusion of dyes. Erythrosine and red gardenia's effective diffusion coefficients in cherry skin were between 1 and up to 2 orders of magnitude lower compared to those in cherry flesh, probably due to the barrier effect provided by the cherry’s epidermis.