Astaxanthin is a carotenoid with a number of assets useful for the food, cosmetic and pharmaceutical industries. Nowadays, it is mainly produced by chemical synthesis. However, the process leads to an enantiomeric mixture where the biologically assimilable forms (3R, 3′R or 3S, 3′S) are a minority. Microbial production of (3R, 3′R) astaxanthin by Xanthophyllomyces dendrorhous is an appealing alternative due to its fast growth rate and easy large-scale production. In order to increase X. dendrorhous astaxanthin yields, random mutant strains able to produce from 6 to 10 mg/g dry mass have been generated; nevertheless, they often are unstable. On the other hand, site-directed mutant strains have also been obtained, but they increase only the yield of non-astaxanthin carotenoids. In this review, we insightfully analyze the metabolic carbon flow converging in astaxanthin biosynthesis and, by integrating the biological features of X. dendrorhous with available metabolic, genomic, transcriptomic, and proteomic data, as well as the knowledge gained with random and site-directed mutants that lead to increased carotenoids yield, we propose new metabolic engineering targets to increase astaxanthin biosynthesis.

In this study, a low-cost chemically defined (CD) culture medium was proposed and evaluated with the aim of replacing culture media such as yeast mold (YM) and yeast peptone dextrose (YPD), commonly used for growth and carotenoid production by Xanthophyllomyces dendrorhous. Initially, the CD culture medium was compared to the YM and YPD. The growth in optical density (OD) and carotenoid production (mg/L) of the cultures reached 4.88, 6.76, 5.79, and 0.67, 0.92, and 0.69, respectively. The CD culture served as the basis of an improved specific culture medium containing industrial glucose. Additionally, in this new formulation, vitamins, glutamate, and other compounds were evaluated. Industrial glucose more than doubled carotenoid production; however, the addition of vitamins was not essential for X. dendrorhous cultivation. Moreover, glutamate and Na2HPO4 proved to be highly significant factors (p-value < 0.05), increasing carotenoid biosynthesis from 0.67 to 1.33 mg/L. The specific culture was successfully used in a bioreactor at 2 L and 110 L pilot-scale levels, increasing carotenoid production up to 2 mg/L. It was demonstrated that the CD-specific culture medium is an efficient alternative to conventional culture media to carry out carotenoid production at the laboratory and pilot levels, with promising potential for industrial scaling.

Xanthophyllomyces dendrorhous is one of the most attractive natural sources of astaxanthin. The yeast produces the compound intracellularly, therefore, it is necessary to evaluate cell rupture methods using clean and efficient technologies for its extraction and it subsequent use in industries. At present work, two non‐conventional high‐pressure extraction methods were evaluated for astaxanthin recovery: Supercritical fluid extraction and microfluidisation. Results: Effect of pressure (15, 30, and 45 Megapascals; MPa), Temperature (313 and 343 °K) and usage of co‐solvent were studied in supercritical extraction process, meanwhile the effect of microfluidisation process (five stages and 160 MPa) for cell rupture and its combination with conventional technics (lithic enzymes, glass beads and ultrasonication) for the recovery of astaxanthin were evaluated. Supercritical fluid extraction presented a higher astaxanthin recovery, 54% yield extraction, at 32.5 MPa and 313 °K, and using ethanol as co‐solvent, compared to a 31% yield extraction by mean microfluidisation process at 160 MPa combined with 15 min of sonication (amplitude of 80%).

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