Abstract
Carotenogenic yeasts are non-conventional oleaginous microorganisms capable of utilizing various waste substrates. In this work, four red yeast strains (Rhodotorula, Cystofilobasidium, and Sporobolomyces sp.) were cultivated in media containing crude, emulsified, and enzymatically hydrolyzed animal waste fat, compared with glucose and glycerol, as single C-sources. Cell morphology (cryo-SEM (cryo-scanning electron microscopy), TEM (transmission electron microscopy)), production of biomass, lipase, biosurfactants, lipids (gas chromatography/flame ionization detection, GC/FID) carotenoids, ubiquinone, and ergosterol (high performance liquid chromatography, HPLC/PDA) in yeast cells was studied depending on the medium composition, the C source, and the carbon/nitrogen (C/N) ratio. All studied strains are able to utilize solid and processed fat. Biomass production at C/N = 13 was higher on emulsified/hydrolyzed fat than on glucose/glycerol. The production of lipids and lipidic metabolites was enhanced for several times on fat; the highest yields of carotenoids (24.8 mg/L) and lipids (54.5%/CDW (cell dry weight)) were found in S. pararoseus. Simultaneous induction of lipase and biosurfactants was observed on crude fat substrate. An increased C/N ratio (13–100) led to higher biomass production in fat media. The production of total lipids increased in all strains to C/N = 50. Oppositely, the production of carotenoids, ubiquinone, and ergosterol dramatically decreased with increased C/N in all strains. Compounds accumulated in stressed red yeasts have a great application potential and can be produced efficiently during the valorization of animal waste fat under the biorefinery concept.
Highlights
In Europe, approximately 16 million tonnes of animal fat by-products are processed annually by fat processors and renderers, with Germany, France, the UK, and Spain as the main processing countries [1]
Based on the glycerol concentration formed during the hydrolysis of animal fat (Table 4), and to the degree of hydrolysis (Figure 1), the enzyme from Candida rugosa (Sigma-Aldrich) was evaluated as the best choice
The amount of glycerol obtained from the degradation of animal fat was the highest (Table 4), and, the rest of the partially degraded lipids could serve as emulsification agents
Summary
In Europe, approximately 16 million tonnes of animal fat by-products are processed annually by fat processors and renderers, with Germany, France, the UK, and Spain as the main processing countries [1]. According to the Animal By-Products Regulations (1069/2009, 142/2011), animal fat by-products are divided into three categories. Category 2 material comprises condemned slaughterhouse fat by-products and dead farm stock, which, in addition to energy generation, may be used for technical applications. Category 3 material is edible fat, which is exclusively derived from approved animals and is obtained from slaughtered animals [2]. In Europe, about 26% (806,000 tons) of animal slaughter fat by-products are classified as category 3 fat materials, according to EU regulations [1]. In addition to category 3 fat, 57% (1.5 million tons) of the total animal fat production accounts for edible animal fat, i.e., fat approved for human consumption [2,3]. Meat production is expected to grow [2]
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