Dynamics of Drying Turmeric Rhizomes (Curcuma longa L.) with Respect to Its Moisture, Color, Texture and Quality

Drying involves removing moisture from food. Therefore, to preserve the phenolic and bioactive compounds such as curcumin, dimethoxy curcumin and bisdemethoxi curcumin, etc., an efficient drying method is considered necessary. The primary drying methods are sun drying, hot air oven drying and fluidized bed drying. Traditional drying methods result in the loss of volatile oil (up to 25%) by evaporation and destruction of some light-sensitive oil constituents. Three methods of drying Turmeric with pretreatments boiled/unboiled and whole/sliced (2.5 cm long) were compared on physical and quality parameters. Texture analysis from sundry sliced boiled rhizomes achieved maximum peak force (45.40 kg), which was an indication of maximum uniform drying. Moisture content was strongly and significantly associated with drying time in different drying methods. Out of the three drying methods, in general, the sun drying showed a declining trend of L*, a* and b* values with drying time. Whereas a slower rate of decrease in L*, a* and b* values was predominant in the oven dry method. Interestingly, in the case of the fluidized method, almost static L*, a* and b* values were measured at 3 h of drying onwards after a declining trend of those values. In the case of sun and oven drying, the hue angle reached its peak at the fourth hour of drying, then gradually declined up to final drying. However, for fluidized bed drying, it had a continuous declining trend for other parameters such as chroma and total color change; there was a sharp decreasing trend for all throughout. Turmeric whole boiled dried in the sun produced the maximum curcumin (5.82%) and the sliced boiled ones produced the maximum oleoresin (8.10%), indicating good quality powdered product among all other drying treatments. Considering all the aspects, it is recommended that sun drying should be followed in post-harvest operations, as it produces a quality powder with comparatively more curcumin, despite its longer drying time.