Microalgae (including the cyanobacteria) are established commercial sources of high-value chemicals such as β-carotene, astaxanthin, docosahexaenoic acid, eicosahexaenoic acid, phycobilin pigments and algal extracts for use in cosmetics. Microalgae are also increasingly playing a role in cosmaceuticals, nutraceuticals and functional foods. In the last few years, there has been renewed interest in microalgae as commercial sources of these and other high-value compounds, driven in part by the attempts to develop commercially viable biofuels from microalgae. This paper briefly reviews the main existing and potential high-value products which can be derived from microalgae and considers their commercial development with a particular focus on the various aspects which need to be considered on the path to commercialisation, using the experience gained in the commercialisation of existing algae products. These considerations include the existing and potential market size and market characteristics of the product, competition by chemically synthesised products or by ‘natural’ compounds from other organisms such as fungi, bacteria, higher plants, etc., product quality requirements and assurance, and the legal and regulatory environment.

High-value products from microalgae—their development and commercialisation

Astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione), a high-value ketocarotenoid with a broad range of applications in food, feed, nutraceutical, and pharmaceutical industries, has been gaining great attention from science and the public in recent years. The green microalgae Haematococcus pluvialis and Chlorella zofingiensis represent the most promising producers of natural astaxanthin. Although H. pluvialis possesses the highest intracellular astaxanthin content and is now believed to be a good producer of astaxanthin, it has intrinsic shortcomings such as slow growth rate, low biomass yield, and a high light requirement. In contrast, C. zofingiensis grows fast phototrophically, heterotrophically and mixtrophically, is easy to be cultured and scaled up both indoors and outdoors, and can achieve ultrahigh cell densities. These robust biotechnological traits provide C. zofingiensis with high potential to be a better organism than H. pluvialis for mass astaxanthin production. This review aims to provide an overview of the biology and industrial potential of C. zofingiensis as an alternative astaxanthin producer. The path forward for further expansion of the astaxanthin production from C. zofingiensis with respect to both challenges and opportunities is also discussed.

https://keep.lib.asu.edu/_flysystem/fedora/c160/Chlorella_zofingiensis_2014.pdf

Chlorella zofingiensis as an Alternative Microalgal Producer of Astaxanthin: Biology and Industrial Potential

By-products may constitute as much as 70% of fish and shellfish after industrial processing and much focus has been on converting these into commercial products. The aim of this paper is therefore to evaluate important challenges and to consider the most realistic options in the use of by-products. Certain by-products like heads, frames and off-cuts from filleting of fish may be used directly as food while by-products in general can be transformed into feed ingredients e.g. for the expanding aquaculture industry. Although sometimes suggested, it is unlikely that by-products can be used to any large extent to produce high-priced products.

Challenges and realistic opportunities in the use of by-products from processing of fish and shellfish

Carotenoids are terpenoid pigments widespread in nature, produced by bacteria, fungi, algae and plants. They are also found in animals, which usually obtain them through the diet. Carotenoids in plants provide striking yellow, orange or red colors to fruits and flowers, and play important metabolic and physiological functions, especially relevant in photosynthesis. Their functions are less clear in non-photosynthetic microorganisms. Different fungi produce diverse carotenoids, but the mutants unable to produce them do not exhibit phenotypic alterations in the laboratory, apart of lack of pigmentation. This review summarizes the current knowledge on the functional basis for carotenoid production in fungi. Different lines of evidence support a protective role of carotenoids against oxidative stress and exposure to visible light or UV irradiation. In addition, the carotenoids are intermediary products in the biosynthesis of physiologically active apocarotenoids or derived compounds. This is the case of retinal, obtained from the symmetrical oxidative cleavage of β-carotene. Retinal is the light-absorbing prosthetic group of the rhodopsins, membrane-bound photoreceptors present also in many fungal species. In Mucorales, β-carotene is an intermediary in the synthesis of trisporoids, apocarotenoid derivatives that include the sexual hormones the trisporic acids, and they are also presumably used in the synthesis of sporopollenin polymers. In conclusion, fungi have adapted their ability to produce carotenoids for different non-essential functions, related with stress tolerance or with the synthesis of physiologically active by-products.

Biological roles of fungal carotenoids.

Metabolic engineering of microorganisms for the synthesis of plant natural products

The oxygenated β-carotene derivative astaxanthin exhibits outstanding colouring, antioxidative and health-promoting properties and is mainly found in the marine environment. To satisfy the growing demand for this ketocarotenoid in the feed, food and cosmetics industries, there are strong efforts to develop economically viable bioprocesses alternative to the current chemical synthesis. However, up to now, natural astaxanthin from Haematococcus pluvialis, Phaffia rhodozyma or Paracoccus carotinifaciens has not been cost competitive with chemically synthesized astaxanthin, thus only serving niche applications. This review illuminates recent advances made in elucidating astaxanthin biosynthesis in P. rhodozyma. It intensely focuses on strategies to increase astaxanthin titers in the heterobasidiomycetous yeast by genetic engineering of the astaxanthin pathway, random mutagenesis and optimization of fermentation processes. This review emphasizes the potential of P. rhodozyma for the biotechnological production of astaxanthin in comparison to other natural sources such as the microalga H. pluvialis, other fungi and transgenic plants and to chemical synthesis.

Markus Hümbelin

Papers

Biotechnological production of astaxanthin with Phaffia rhodozyma / Xanthophyllomyces dendrorhous