Abstract

The thin layer drying behavior of lettuce leaves was investigated using an indirect pilot solar dryer with thermal energy storage in water, equipped with solar collectors and photovoltaic cells. The drying procedure consisted of shredded lettuce leaves, temperature <= 52 degrees C, airspeed, 1.0 m center dot s(-1), and process time similar to 10.0 h. Fifteen drying models were adjusted to the experimental data obtained; three models with maximum values of coefficient of determination (R-2)-Page, Midilli, and Kucuk, and Weibull Distribution, whose values of R-2 >= 0.998, and other statistical parameters, chi(2), SSE, and RMSE values closer to zero were chosen. The initial browning index BI = 120.5 +/- 0.7 decreased compared to the dry sample BI = 78.99 +/- 0.5, with chromatic coordinate degradations a* and b*; but not the luminosity L*; where Delta E = 8.26; whose meaning is that the dry sample is a "more opaque brownish color" due to the difference in the chroma Delta C = 6.65, and with a change from the yellow-green to yellow-red zone, and a difference in hue angle, Delta h degrees = 14.27, between the fresh and the dried sample. D-eff values for shredded lettuce leaves were 1.8 x 10(-9) m(2) s(-1) for values <= 52 degrees C.