Microalgae Derived Astaxanthin: Research and Consumer Trends and Industrial Use as Food

Astaxanthin is a high-value carotenoid currently being produced by chemical synthesis and by extraction from the biomass of the microalga Haematococcus pluvialis. Other microalgae, such as Chlorella zofingiensis, have the potential for being used as sources of astaxanthin. The differences between the synthetic and the microalgae derived astaxanthin are notorious: not only their production and price but also their uses and bioactivity. Microalgae derived astaxanthin is being used as a pigment in food and feed or aquafeed production and also in cosmetic and pharmaceutical products. Several health-promoting properties have been attributed to astaxanthin, and these were summarized in the current review paper. Most of these properties are attributed to the high antioxidant capacity of this molecule, much higher than that of other known natural compounds. The aim of this review is to consider the main challenges and opportunities of microalgae derived products, such as astaxanthin as food. Moreover, the current study includes a bibliometric analysis that summarizes the current research trends related to astaxanthin. Moreover, the potential utilization of microalgae other than H. pluvialis as sources of astaxanthin as well as the health-promoting properties of this valuable compound will be discussed.

Xanthophylls from the Sea: Algae as Source of Bioactive Carotenoids

Algae are considered pigment-producing organisms. The function of these compounds in algae is to carry out photosynthesis. They have a great variety of pigments, which can be classified into three large groups: chlorophylls, carotenoids, and phycobilins. Within the carotenoids are xanthophylls. Xanthophylls (fucoxanthin, astaxanthin, lutein, zeaxanthin, and β-cryptoxanthin) are a type of carotenoids with anti-tumor and anti-inflammatory activities, due to their chemical structure rich in double bonds that provides them with antioxidant properties. In this context, xanthophylls can protect other molecules from oxidative stress by turning off singlet oxygen damage through various mechanisms. Based on clinical studies, this review shows the available information concerning the bioactivity and biological effects of the main xanthophylls present in algae. In addition, the algae with the highest production rate of the different compounds of interest were studied. It was observed that fucoxanthin is obtained mainly from the brown seaweeds Laminaria japonica, Undaria pinnatifida, Hizikia fusiformis, Sargassum spp., and Fucus spp. The main sources of astaxanthin are the microalgae Haematococcus pluvialis, Chlorella zofingiensis, and Chlorococcum sp. Lutein and zeaxanthin are mainly found in algal species such as Scenedesmus spp., Chlorella spp., Rhodophyta spp., or Spirulina spp. However, the extraction and purification processes of xanthophylls from algae need to be standardized to facilitate their commercialization. Finally, we assessed factors that determine the bioavailability and bioaccesibility of these molecules. We also suggested techniques that increase xanthophyll’s bioavailability.

The effect of diverse nitrogen sources in the nutrient medium on the growth of the green microalgae Chromochloris zofingiensis in the batch culture

The effect of three nitrogen (N) sources in the nutrient medium – sodium nitrate (NaNO3), urea (CO(NH2)2), and ammonium chloride (NH4Cl) – on the morphological and physiological characteristics of the green microalga Chromochloris (Chlorella) zofingiensis, a potential commercial producer of lipids and a ketocarotenoid astaxanthin, was studied. The alga was batch-cultivated in glass conical flasks from starting cell density (n) around 2.3·106 per mL and dry weight (DW) content of 0.06 g·L−1 in all variants at 120 μmol·m−2·s−1 PAR, +20…+21 °C, and air bubbling at a rate of 0.3 L·min−1·L−1. The concentration of nitrogen sources (as elemental N) in the modified BBM nutrient medium was 8.83 mmol·L−1, the cultivation duration was 17 days. The dynamics of n and cell volumes, DW content, chlorophylls a and b (Chla and Chlb), total carotenoids (Car), and lipids (Lip) in the cultures, concentration of N sources in the nutrient medium, and its pH were recorded. It was shown that the growth rate, size distribution of the cell populations, and the biomass chemical composition depended significantly on the nitrogen source in the nutrient medium. Using NH4Cl as N source caused on the second day growth inhibition, cell swelling, aggregation, and discoloration; by the seventh day, it caused culture crash. C. zofingiensis cells took up NaNO3 and CO(NH2)2 from the medium at a similar rate (0.626 and 0.631 mmol N·L−1·day−1, respectively), but the growth of the culture fed with CO(NH2)2 lagged; its cell volume and Chla, Chlb, and total Car contents declined profoundly. The average dry matter productivity (PDW) in the culture grown on CO(NH2)2 [(0.086 ± 0.004) g·L−1·day−1] was 32.6 % lower than in the culture grown on NaNO3 [(0.114 ± 0.005) g·L−1·day−1]. At the same time, lipid productivity (PLip) of the urea-fed culture was comparable with that of the nitrate-fed culture (PLip of 28 and 26 mg·L−1·day−1, respectively). The lipid DW percentage of the former exceeded significantly that of the nitrate-fed culture (31.6 % vs 23.1 %, respectively). From the standpoint of profitability, the lag in biomass accumulation recorded in the urea-fed culture on PDW is not critical since it is compensated by lowering the cost of nitrogen source for the nutrient medium (approximately by 230 %) and a higher biomass lipid content. C. zofingiensis grown in media with urea as the only N source deserves further investigation.