Because of the biological role of the carotenoids as vitamin A precursors in humans and animals and owing to their antioxidant properties and suspected activity in preventing some forms of cancer as well, carotenoid pigments represent a group of most valuable molecules for industrial applications of red yeasts. The pharmaceutical, chemical, feed and food industries have shown increased interest in the use of carotenoids, mainly as provitamin A, but also as natural food and feed colorants. Accordingly, the red yeast P. rhodozyma is currently used for the production of astaxanthin, an important carotenoid pigment that can be exploite in aquaculture to give an appealing pink color to the fresh of farmed salmonid fish, and it also helps to impart a desirable golden color to the egg yolk and fresh of poultry. Salmon farming is an industry that is growing and gradually replacing the world’s wild salmon fisheries. The most expensive ingredient in salmonid feeds is astaxanthin, and though the actual revenues are privately held, it has been estimated that the market for astaxanthin in >US $100 milion per year (Frengova & Beshkova, 2009). Similarly to Xanthophyllomonas, also other red yeast strains could be used for industrial puropses to pruduction of carotenoids — beta-carotene, torulene, lycopene, as well as further lipid metabolites produced in cells. In many works mostly Rhodotorula glutinis sems to be perspective strain. Combined enrichment of Rhodotorula biomass by provitamin A (carotenes) and provitamin D (ergosterol) could be used in food and feed supplements (Marova et al., 2010), aditional enrichment by Coenzyme Q10 is suitable product for cosmetics and could be used also in food and feed (Dimitrova et al., 2010). Formulas based on selenium-enriched red yeast biomass with enhanced carotenoid content could be used as nutrition suplement too (Breierova et al, 2008). There is also posibility to use oleaginous red yeasts to single cell oil production; in this case production of other lipid metabolites could be reduced and the main flow of acetylCoA will be directed to fatty acid and lipid biosynthesis (Dai et al., 2007).

One limitation impacting the industrial utility of P. rhodozyma/ X. dendrourhous or Rhodotorula species has been hindered absorption of carotenoids, due to the yeast’s thick cell wall. Because of presence of other specific biologically active compounds as well as high level of nutritionally sigificant yeast cell components (proteins, unsaturated fat, vitamins…) the best strategy is to disrupt cells and to use the whole biomass without isolation of individual compounds. The biotechnology industry has developed different means of active compounds liberation by the yeast including optimization of drying conditions, mechanical breakage, microwave treatment and enzyme treatment, as described below (Frengova & Beshkova, 2009).

When disrupted cells P. rhodozyma, without cell walls are added to the diets of animals, astaxanthin is readily absorbed from the gut; it effectively colors the fresh of penreared salmonids, and also helps impart a desirable golden color to the egg yolk and fresh of poultry. Astaxanthin in yeast (X. dendrorhous) prepared by spray drying and Xat-roller milling was well absorbed by laying hens and was successfully used as a pigmentation agent in animals (An, 2005). Specifically, when spray-dried and milled yeast was supplied in the feed (40 mg astaxanthin/kg feed), astaxanthin was successfully absorbed (1,500 ng/ ml blood and 1,100 ng/ g skin) by laying hens. Extrusion temperature did not affect utilization of dietary astaxanthin or rainbow trout fresh color significantly, but cell wall disruption of red yeast cells was critical to optimize carotenoid utilization. Increasing the degree of enzymatic cell wall disruption increased fresh astaxanthin concentrations from 2.2 to 6.7 mg/kg, redness values from 5.5 to 10.7, yellowness values from 11.7 to 16.7 and astaxanthin retentions in the muscle from 3.7 to 17.4%. A formulation of P. rhodozyma cells blended with ethoxyquin, lecithin and oil prior to drying also increased astaxanthin deposition in salmonid fish fresh and rainbow trout fresh when supplied in feed as an additive. Absorption and accumulation of biological astaxanthin were higher thah those of chemical astaxanthin, probably because of the high contents of lipids in the yeast (17%). Lipid peroxide formation in skin was significantly decreased by astaxanthin. The peroxide production in chickens fed chemical astaxanthin was markedly lowered compared to biological astaxanthin (Frengova & Beshkova, 2009) .

The levels of serum transaminase activities and of lipid peroxides in fish fed oxidized oil were significantly higher that those of the control fish fed non-oxidized oil. However, the supply of freeze-dried red yeast preparation considerably decreased both enzyme activities and lipid peroxides level. Furthermore, the serum lipid (triglycerides, total cholesterol and phospholipids) concentrations were also significantly decreased. Especially, the serum triglyceride level of fish fed the red yeast was as low as that of the control. Recently was found that Zn2+ ions induced changes in yeasts (R. glutinis and R. rubra) leading to more efficient scavenging and antioxidant capacities compared with Ni2+ ions, and antioxidants (carotenoids) present in yeast’s walls showed higher ability to scavenge free radicals than those from inside the cells (Rapta et al., 2005). Later, the in vivo antioxidant and protective effects of astaxanthin isolated from X. dendrorhous against ethanol-induced gastric mucosal injury were established in animal models, especially rats (Kim et al., 2005). Oral administration of astaxanthin showed significant protection against ethanol-induced gastric lesion and inhibited elevation of the lipid peroxide levels in gastric mucosa. A histologic examination clearly indicated that the acute gastric mucosal lesion induced by ethanol nearly disappeared after pretreatment with astaxanthin (Frengova & Beshkova, 2009).

Chemopreventive and anticarcinogenic effects of carotenoids by Rhodotorula on the development of preneoplastic lesions during N-nitrosodiethylamine (DEN)-induced hepatocarcinogenesis in female Wistar strain rats were also studied (Bhosale et al., 2002). Spray-dried yeast R. glutinis (containing carotenoid pigments torulene, torularhodin and beta-carotene in proportion 58:33:2) showed significant effect on the prevention of liver tumor development. However, R. glutinis effects were relatively more significant in groups where R. glutinis was administered after DEN treatment, suggesting that R. glutinis is quite effective in the prevention of liver tumor development especially when administered after DEN treatment, indicating possible protective effects at the promotional stages.

3. Conclusions

Yeast is, due to its physiological properties, widely used in the food, feed, chemical and pharmaceutical industries for production of various valuable compounds. Red yeast is well known producer of carotenoids which are significant because of their activity as vitamin A precursors, colorants, antioxidants and possible tumor-inhibiting agents. Biological sources of carotenoids receive major focus nowadays because of the stringent rules and regulations applied to chemically synthesized/purified pigments. Compared with the extraction from vegetables, the microbial production of carotenoids is of paramount interest, mainly because of the problems of seasonal and geographic variability in the production and marketing of several of the colorants of plant origin. Moreover, red yeast is a rich source of other specific compounds — ergosterol, Coenzyme Q10, as well as unsaturated fatty acids, fats, proteins and vitamins and can be incorporated in feeds to enhance the nutritional value of yeast biomass. One limitation impacting the industrial utility of carotenogenic yeast has been complicated liberation and bioavailability of carotenoids and other active compounds, due to the yeast’s thick cell wall. The biotechnological industry has developed different means of pigment liberation by the yeast including optimization of drying conditions, mechanical breakage, microwave treatment and enzyme treatment.

The other very important limitation involved in the practical exploitation of yeasts is the high cost of microbial production. The production cost could be reduced by increasing yields of product, as well as using less expensive substrates. There is a need to improve fermentation strategies. Biomass and metabolites production by red yeast is highly variable and can be influenced by cultivation conditions (light, temperature, pH, aeration etc.). Different approaches for improving the production properties of the yeast strains, such as environmental stress, mutagenesis or genetic modification, have been studied and optimized. The other possibility for production cost reduction is using various low-cost materials as carbon or nitrogen source. The potential of several waste materials (whey, potato mass, apple mass and various cereals) as substrates for carotenoid and ergosterol production by some yeast strains belonging to the genus Rhodotorula and Sporobolomyces were succesfully examined. Mild nutrition stress cause by several waste substrates was found to be the suitable induction factor for higher carotenogenesis and ergosterol production in red yeasts.

Environmental stress was reported to induce carotenoid, ergosterol and lipid production as part of red yeast stress response. Under stress cells posses altered phenotype biotechnologically significant and/or undesirable in a dose-dependent manner. Phenotypic profiling of the environmental stress responses demonstrates genetic susceptibility of yeast to environmental stress. Low concentrations of oxidative and osmotic stress, which can under specific conditions induce carotenogenesis, have no significant effect on yeast growth. Red yeast cultivated under osmotic and oxidative stress or on various waste substrates shows no significant differences in cell morphology when compared with yeast cultivated in conventional glucose medium under optimal conditions. Thus, low environmental stress can be used for induction of carotenogenesis and use of non-toxic stress factors (salt, metals) can enable utilization o whole cell biomass to industrial use. Simple and cheap stress factor in relatively low concentration can substantially enhance biotechnologically significant metabolite production.

Growing interest in pigment and other metabolite applications in various fields coupled with their significance in health and dietary requirements has encouraged "hunting" for more suitable sources of these compounds. Due to restrictions, there is no possibility to apply carotenoids prepared by chemical synthesis for food, pharmaceutical and medical purposes. However, the success of microbial pigments, metabolites and single cell oils depends upon their acceptability in the market, regulatory approval, and the size of the capital investment required to bring the product to market. Therefore, the focus of biotechnology on highly valuable yeast biomass requires knowledge how microorganisms control and regulate the biosynthetic machinery in order to obtain metabolites and enriched biomass in high yield and at low price. From this view, attempts have been directed at the development and improvement of biotechnological processes for the utilization of red yeasts on an industrial scale. Current successes using mutation methods and molecular engineering techniques carried out over recent years have not only answered some fundamental questions related to pigment formation but has also enabled the construction of new microbial varieties that can synthesize unusual carotene metabolites. Elucidation of these mechanisms represents a challenging and potentially rewarding subject for the further research and may finally allow us to move from empirical technology to predictable carotenoid and/or isoprenoid metabolite design. Thus, the manipulation and regulation of red yeast metabolism open a large number of possibilities for academic research, demonstrates the enormous potential in its application and creates new economic competitiveness and market of microbial lipid compounds.