Effects of LED Spectra on Biochemical and Histological Profiles of Eurycoma longifolia Hairy Root Cultures

The roots of Eurycoma longifolia Jack, commonly used in traditional Malaysian medicine, are known for their aphrodisiac properties and anti-cancer potential. Hairy root culture (HRC) represents a sustainable and promising platform for the enhanced production of secondary metabolites. This study explored the impact of different light emitting diode (LED) treatments on Elongifolia hairy root cultures (ELHRCs) over 12 weeks. Five LED spectra were used: red (R), blue (B), mint green (MG), blue plus red in a 1:1 ratio (BR) and white (W, as control). The study aimed to evaluate the effects of these light treatments on quantified histological characteristics, total carbohydrate and protein content, and antioxidant activity of ELHRCs at 8 weeks, 10 weeks and 12 weeks of culture. Quantitative five-directional radial histological analysis revealed notable tissue repartitioning; specifically, the MG treatment exhibited the highest cortical expansion (~400 μm) alongside a reduction in vascular radius relative to the W control. These structural modifications corresponded to distinct biochemical shifts. The results showed that the W control and BR light treatment significantly maintained the highest protein content across all culture durations, with maximum concentrations of 0.707 ± 0.07 mg/mL and 0.706 ± 0.01 mg/mL, respectively. Meanwhile, compared to the W control, R and B light treatment promoted higher carbohydrate accumulation, particularly after 8 weeks and 12 weeks, with values reaching 116.79 ± 4.34 mg/mL and 103.68 ± 15.15 mg/mL. Antioxidant activity, measured through DPPH radical scavenging, was nominally highest under R light after 8 weeks and 10 weeks (92.13% and 90.28%, respectively), though these values were not significantly different from the W control. These findings highlight the potential of LED treatments to optimise metabolite production in hairy root cultures, offering insights into improving bioactive compound yield for pharmaceuticaland nutraceutical applications.