Color and Mass Transfer Kinetics During Air Drying of Pretreated Oyster Mushrooms (Pleurotus ostreatus spp.)

The color and mass transfer kinetics during air drying as well the desorption isotherms at 40, 50, and 60 degrees C of Pleurotus ostreatus mushrooms were studied. Blanched and sulfated mushrooms were tested against untreated samples to study the browning development. The analysis of sorption isotherms based on the Blahovec-Yanniotis model provided insight into the sorption mechanisms, the shape of the sorption isotherms, and the diffusion coefficient decrease at the later stages of the drying. The mean thickness of the samples decreased by 50% during drying, which dictates the necessity to include shrinkage in the mass transfer analysis. The estimated diffusivities were 2.89x10(-11)-2.20x10(-10)m(2)/s for sulfated mushrooms, 3.75x10(-11)-1.69x10(-10)m(2)/s for blanched mushrooms, and 3.62x10(-11)-2.11x10(-10)m(2)/s for untreated mushrooms. An analytical solution of Fick's second law employing a modified method of slopes and considering the shrinkage effect was used to estimate the nonlinear water diffusion. The statistical analysis showed that drying temperature and pretreatment significantly interaction affected water diffusivity. Color analysis was based on reduced lightness (L-t(*)/L-0(*)) and Browning index (BI) change with time, temperature, and pretreatment. The difference in the of blanched mushrooms from sulfated and untreated samples was decreased as drying temperature increased. The BI change was modeled by a new first-order kinetics model. The estimated energy of activation (E-a) values were 44.8, 32.5, and 28.0 kJ/mol for untreated, blanched, and sulfated mushrooms, respectively. The E-a values show that untreated mushrooms are more sensitive to temperature change than the pretreated mushrooms during thermal processing.