Monitoring of active constituents of turmeric (Curcuma longa L.) rhizome stored under supplemented white LED-light with different light intensities

Previous research showed possible applications of supplemented light to increase active compounds in harvested underground part of medicinal plants. Accordingly, the effect of supplementing white LED (light emitting diode) at different light intensities on the main constituents (curcumin, demethoxycurcumin, bisdemethoxycurcumin) of turmeric (Curcuma longa L.) rhizomes was investigated every week during storage. Rhizomes were stored for six weeks at room temperature of 24.7-34.5°C and 56-76% RH. During storage, rhizomes were illuminated with varied number (0 (control), 1, 2 or 3 tube (s)) of white LEDs at light intensities of 0 µmol m‑2 s‑1, 14-15 µmol m‑2 s‑1, 41-42 µmol m‑2 s‑1 and 61-62 µmol m‑2 s‑1, respectively. The LEDs were operated for 6 h (3:00 to 6:00 am and 6:00 to 9:00 pm) daily. Concentrations of curcuminoid, crude extracts and volatile oil fluctuated during storage. There was an increase in these attributes during the first week of storage and then a decline thereafter till week 4. The highest increase in all parameters occurred in week 5 and decreased at week 6 where there were significant differences among treatments (p<.05). Under the treatment using 61-62 µmol m‑2 s‑1 of white light LEDs, curcuminoid content (4.42% w/w) and crude extract (5.72% w/v) were 10.78 and 16.02% greater than the control. There was no significant difference in volatile oil content (1.10-2.10%).