## 9 Metabolic Features and By-Products from _Candida stellata_ Activity
### Production of Sophorolipids Biosurfactants by Candida  
The worldwide production of surfactants is about 10 million tons per year, divided between domestic and laundry detergents and different industrial applications. Currently, the surfactants are usually petroleum-derived, although the aim is to produce these compounds from renewable substances. Sophorolipids (SLs), which are composed of sophorose (a dimeric sugar) linked to a long-chain hydroxy fatty acid, are good candidates as surfactant product from renewable sources. These molecules are produced in high concentrations by phylogenetically diverse group of yeasts [122], and their biosynthesis is clearly influenced by aeration, initial glucose concentration, and pH values [123; 124]. SLs present two different forms: a closed lactone and an open acidic form. Each form has different properties: Lactonic SLs have antimicrobial activity and are better in surface tension reduction, while acidic SLs have better foaming attributes [122]. The yeast _S. bombicola_ has been widely studied as a major producer of SLs together with _Candida apicola_ within _Starmerella_ clade [122]. The highest _C. bombicola_ (ATCC 22214) SL yield of 400 g/L was obtained when corn oil and honey served as the carbon sources [125]; also, [PERSON] and [PERSON] [126] showed that the same strain synthetized SLs with antibacterial activity mainly against Gram-positive bacteria. In a study with 19 species of _Starmerella_ yeast clade [123], _C. stellata_ NRRL Y-1446 strain from Rovello bianco grape variety was one of 19 species with a significant production of SLs with 11.9 g/L predominantly as di-\(O\)-acetyl free-acid form, plus lesser amounts of mono-\(O\)-acetyl and non-acetyl SLs. [PERSON] et al. [124] obtained similar SLs concentration (18.2 g/L) using _S. bombicola_ NRRL Y-17069 and determining the optimal fermentation method to generate these surfactant compounds. Recently, a novel lactone esterase enzyme from _S. bombicola_, which catalyzes the intramolecular lactonization of acidic SLs in an aqueous environment, is being investigated to become an ecological tool in industry applications [127]. Co-Fermentations between _Candida stellata_ and _Saccharomyces cerevisiae_: A Way against Standardized Wines  
The use of co-fermentation strategies between non-_Saccharomyces_ and _S. cerevisiae_ yeast species in a controlled manner can be a useful tool for wine production. Several aspects support this consideration, such as  
1. Effect on some analytical compounds as increased glycerol concentration, enhanced total acidity, and reduced acetic acid concentration of wine. 2. Enhancement of desirable aromatic compounds (esters, volatile thiols). 3. Reduction of final ethanol content of the wine. 4. Improvement of complexity and overall quality of wine. 5. Larger release of polysaccharides (mannoproteins). In the last few years, the use of _C. stellata_ yeast in multi-starter fermentations with _S. cerevisiae_ has been widely investigated for its ability to increase the glycerol content in wines and their special fructophilic character [66], its capacity to contribute to greater aroma complexity of the wine [128], and its capacity to minimize the risk of fermentation problems [68]. [PERSON] and [PERSON] [66] carried out mixed and sequential fermentations with _C. stellata_ and _S. cerevisiae_; the final wines were rich in glycerol and succin acid, and with less alcohol and acetic acid in comparison with the mono-inoculated _S. cerevisiae_ control. [PERSON] et al. [68] concluded that _S. bombicola_ influenced the alcohol production ability of _S. cerevisiae_ under mixed inoculation, since pyruvate decarboxylase (Pdc1) activity in mixed fermentation was lower than pure culture of _S. cerevisiae_, while alcohol dehydrogenase (Adh1) activity showed opposite behavior. The wines made through _C. stellata_/_S. cerevisiae_ co-fermentations usually present higher aroma complexity and overall quality.