Effect of solar drying methods on color kinetics and texture of dates

Abstract

The present work investigates the effect of solar drying methods on the color and textural attributes of Khalas dates at three ripening stages (khalal, rutab and tamr) and evaluates color change kinetics using three kinetic models. Three solar drying methods, namely, open sun drying (OSD), forced convective drying (FCD) and greenhouse tunnel drying (GTD) were studied. The drying methods and ripening stages had significant effect on all color attributes. Khalal stage dates dried in FCD had the lowest color variations (L*: −12%, a*: +4%, b*: −46%, chroma: −38%, hue angle: −21% and total color change, ΔE:14.05) and thus, the highest color stability. At the end of drying, color of rutab and tamr stage dates changed red-brown in all the three drying methods due to the massive loss of b* (88–92%) and hue angle (63–73%), and altering hue angle from 23° (tamr fresh) to 9–12° (dried), respectively. The most appropriate model to describe the color change kinetics of dates at the three ripening stages was the fractional conversion model. The texture profile analysis revealed that FCD produced the softest dates for all the three ripening stages (hardness ranged 2.52–3.42 N). Overall, dates dried in FCD had the best color and textural properties as compared to the OSD and GTD dried dates in all ripening stages.