Impact of Light Emitting Diode (LED) irradiation on growth, biochemical, antioxidant, and antibacterial activity of Scenedesmus sp

Abstract

Different LED wavelengths, red at 635 nm, blue at 447 nm and mixed wavelength irradiation either sequential red-blue or simultaneous red-blue for different exposure times (30, 60 and 90 min) were investigated for their effect on the growth, cell size, pigment accumulation, total carbohydrate and protein content of the micro alga, Scenedesmus sp. Bioactive secondary metabolites including phenolics, flavonoids, saponins and tannins were estimated. In addition, antioxidant and antibacterial activities of methanolic algal extract were detected. Exposure to 30 min of red wavelength and 60 min in case of blue and mixed wavelengths exhibited maximum growth of Scenedesmus sp. Exposure duration for 90 min to different wavelengths decreased cell size of Scenedesmus sp. as compared with non-treated cells. In addition, accumulation of chlorophyll a, b, and carotenoids was in the following order: M (sequential red-blue) > R + B (simultaneous red-blue) > blue > red > control. A noticeable increase in total carbohydrate content was observed in all treatments, except, the blue wavelength treatment (B) in comparison to the control. The maximum protein content was recorded under control and blue LED illumination. Flavonoid content was markedly increased in all treatments compared to the control however, phenolic content was significantly reduced. Exposure of Scenedesmus sp. to blue LED for 60 min was positively linked to the enhancement of bioactive antioxidants. Exposure of Scenedesmus sp. to red LED for 30 min was linked to strong antibacterial activity. Further research is required to elucidate the underlying mechanisms governing algal responses to specific wavelengths.