Effect of Varying Light Spectrum on Antioxidant Production of Red Leaf Lettuces Cultivated using Fish Wastewater

Wavelengths of blue (B) and red (R) light can influence plants growth and development, specifically in the production of antioxidants. This research aims to determine the optimum B and R light percentage to enhance overall growth and antioxidant levels in red leaf lettuces cultivated from fish wastewater (Omnicare Farm, Malaysia). Lettuces were grown under various combinations of light-emitting diode (LED) light treatment (33 % B + 67 % R; 40 % B + 60 % R and 50 % B + 50 % R), in which the light percentages were quantified using light spectrum analyser for 27 days. The photosynthetic photon flux density (PPFD), photoperiod and temperature were maintained at 250 µmol/m2.s, 16 h and 30 ± 3 ºC. Under varying light spectra, the plant growth parameters were studied in terms of length and weight while the leaf surface color was measured for lightness (L*), chroma (C*), hue degree (h°), redness (a*) and yellowness (b*). After the LED treatment, the antioxidant levels were analyzed based on the anthocyanin concentration after the LED treatment. The increased B light percentage from 33 to 50% caused a 91.5 and 71.3% reduction in the overall weight and leaf length. However, it increased the anthocyanin concentration by 6.5-fold. This shows that a higher B light percentage resulted in undesirable red leaf lettuce growth reduction but promoted the production of antioxidant levels (anthocyanin concentration) in the lettuces.