Co-production of high density biomass and high-value compounds via two-stage cultivation of Chlorella vulgaris using light intensity and a combination of salt stressors
Eman A. El-fayoumy, Hamdy Elsayed Ahmed Ali, Khaled Elsaid, Ahmed M. Elkhatat, Saeed Al‐Meer, Mohd Zul Helmi Rozaini, Mohd Azmuddin Abdullah
Abstract
Abstract In this study, the effects of combined stress factors involving light intensity and salinity (NaCl, MgCl 2 , CaCl 2 , and their combinations) on the two-stage cultivation of Chlorella vulgaris for simultaneous production of biomass and high-value products, were investigated. The two-stage strategies comprised a 25-day vegetative stage in BG11 medium, followed by a 15-day combined stress stage. During salt stress conditions, the addition of 15 g L −1 CaCl 2 or 7.5 g L −1 MgCl 2 / 7.5 g L −1 CaCl 2 mixture with 140 µmol m −2 s −1 light intensity significantly promoted the growth of C. vulgaris achieving maximum biomass productivity of 50.50 ± 0.50 and 50.25 ± 3.25 mg L −1 d −1 , respectively. Cultivation of C. vulgaris in a medium containing 7.5 g L −1 NaCl/ 7.5 g L −1 CaCl 2 had remarkably increased the lipid content (31.15 ± 1.18%) and lipid productivity (14.55 ± 1.48 mg L −1 d −1 ). The saturated fatty acids (SFAs) at 39.52–59.29%, monounsaturated fatty acids (MUFAs) at 27.16–35.47%, and polyunsaturated fatty acids (PUFAs) at 7.18–29.97%, were obtained with palmitic (C16:0), oleic (C18:1), stearic (C18:0), and linolenic (C18:3) acids as predominant fatty acids. Cultures supplemented with 5 g L −1 NaCl / 5 g L −1 MgCl 2 / 5 g L −1 CaCl 2 and high light intensity exposure attained consistently high carbohydrate content (52.71 ± 2.50%). The combination of 7.5 g L −1 NaCl / 7.5 g L −1 MgCl 2 also resulted in a marked increase in the protein content (35.32 ± 2.20%) and total carotenoids (0.31 ± 0.03 μg mL −1 ) as compared to the Controls. The highest antioxidant activity (86.16%) was achieved with a 7.5 g L −1 NaCl / 7.5 g L −1 CaCl 2 combination in the growth stage. The antioxidant activities were attributed to the presence of phenolics, flavonoids, and tannins due to the stressed conditions. One of the key benefits of using a combined stress strategy in this study is that if one factor has a low impact on enhancing target metabolites, other factors can compensate.