Yeast need not be used only in beer production. I. The carotenoid astaxanthin produced by yeast.

Carotenoids are produced by photosynthesizing organisms, i.e. plants and algae, as well as some bacteria, protists and fungi. Their role lies mainly in the function of complementary photosynthetic pigments and antioxidants. Carotenoids are distinguished according to their structure into carotenoids of the hydrocarbon type, e.g. α-, β- and γ-carotene and oxygen derivatives – xanthophylls, among which astaxanthin, which excels in its antioxidant and nutraceutical properties, is the most important. It is used as a dietary supplement both in human nutrition and in the aquaculture and poultry industry, as a nutritional supplement in salmonid and hen farming. Many works have focused on the search for natural sources of astaxanthin as an alternative to synthetic astaxanthin. In nature, very few astaxanthin producing organisms are known in non-minor amounts, with green alga Haematococcus pluvialis and the yeast Xanthophyllomyces dendrorhous (anamorph Phaffia rhodozyma) being the most promising microorganisms for the biotechnological production of this xanthophyll. In this review we focus on the biosynthesis and carotenogenesis including the regulation mechanisms, generation of hyperproducing mutants by random mutagenesis and, last but not least, also metabolic engineering (genetic techniques). Attention is also paid to the optimization of fermentation conditions.