Mixotrophic Growth of Astaxanthin-Rich Alga Haematococcus pluvialis using Refined Crude Glycerol as Carbon Substrate: Batch and Fed-Batch Cultivations

Abstract

Due to a current overabundance of crude glycerol produced from the biodiesel industry, the compound has the potential to be used as an inexpensive carbon source for growing the green microalga Haematococcus pluvialis (H. pluvialis), the richest source of natural astaxanthin (ATX). In order to investigate the practical use of crude glycerol, microalgal cultures were grown mixotrophically and heterotrophically in BG11 medium with the supplementation of refined crude glycerol, a mixture of glycerol and ethanol, under 2, 5 and 7 g L-1, using photoautotrophic cultivation as a control. H. pluvialis green-stage growth and red-stage ATX accumulation were effectively facilitated by mixotrophic conditions, with the highest µ of 0.27 ± 0.03 day-1 and the highest ATX content of (3.5 ± 0.4 % wt) (both observed under 7 g glycerol L-1). In contrast, growth was completely inhibited under heterotrophic conditions. Under repeated fed-batch operation, the exponential growth phase, during green-stage mixotrophic cultivation, was significantly extended from 5 days (in batch) to 24 days, making biomass yield of 1.86 ± 0.06 g DCW L-1 (around 2.6-fold higher). Monitoring of substrates (glycerol, ethanol and nitrate) in the broth was carried out and subsequently suggested that further optimization of media could be made.

Effects of Four Organic Carbon Sources on the Growth and Astaxanthin Accumulation of Haematococcus lacustris

“…The culture with 5 g/L glycerol increased the biomass by 34.22% [45]. Glycerol is reportedly superior to acetate in terms of enhancing Haematococcus biomass and astaxanthin production [46]. It is a polar and compatible solute for enzymes and membranes that readily enters algal cells by passive diffusion [47].…”

Improved Production of Astaxanthin from Haematococcus pluvialis Using a Hybrid Open–Closed Cultivation System

“…Therefore, there is high demand for the natural form of astaxanthin, which has not been met due to the arduous procedures required for its manufacture [15][16][17]. The astaxanthin market was valued at USD 1.0 billion globally in 2019 and is projected to increase at a compound annual growth rate of 16.2% to USD 3.4 billion by 2027 [18]. Natural astaxanthin has very powerful antioxidative properties, which have applications in the nutraceutical, cosmetic, and pharmaceutical industries [17,19].…”

“…These agents are important bioactive components in antiaging serums, sunblock creams, and beauty products, and are also provided as oral dietary supplements at a recommended dose of 4 mg per day. They also have anti-gastric, anti-cancer, anti-inflammatory, antidiabetic, anti-obesity, ocular-protective, and immune response-boosting properties, and many studies are currently underway to explore their immense potential for biological applications [17,18,[21][22][23].…”