Exopolysaccharides produced by mixed culture of yeast Rhodotorula rubra GED10 and yogurt bacteria (Streptococcus thermophilus 13a + Lactobacillus bulgaricus 2-11).
OBJECTIVE
The studies of the production of exopolysaccharides by lactose-negative yeast and a yogurt starter co-cultivated in a natural substrate containing lactose may be considered of interest because they reveal the possibilities for high-efficiency synthesis of biopolymers by mixed cultivation.


RESULTS
The mixed culture Rhodotorula rubra GED10 + (Streptococcus thermophilus 13a + Lactobacillus bulgaricus 2-11) was cultivated in cheese whey ultrafiltrate (WU) (44.0 g lactose l(-1)) at initial pH 6.0, 28 degrees C, under intensive aeration (air-flow rate 1.0 l l(-1) min(-1), agitation 220 rev min(-1)) in a MBR AG fermentor. The mixed culture manifested the highest activity for synthesis of exopolysaccharides (19.3 g l(-1)) and cell mass (21.0 g l(-1)) at the 84th hour. The yogurt starter synthesized neutral exopolysaccharides, while the mixed culture yeast + yogurt starter produced acidic exopolysaccharides containing uronic acid (6%). The neutral sugar composition was identified as mannose, glucose, galactose, xylose and arabinose. Mannose dominated in the polymer composition (83%) that was produced only by the yeast (97%).


CONCLUSIONS
Lactose in the WU can be effectively utilized by a co-culture of lactose-negative yeast-yogurt starter for synthesis of exopolysaccharides.


CONCLUSIONS
The present findings propose an alternative use of WU as a cost-effective carbohydrate substrate, and suggest that the lactose-negative yeast Rhodotorula rubra can have industrial application as producers of exopolysaccharides.
Laboratory of Applied Microbiology, Institute of Microbiology, Bulgarian Academy of Sciences, Maritza Blvd., Plovdiv, Bulgaria. lbpmbas@plov.omega.bg
E D
ED
Simova
G I
GI
Frengova
D M
DM
Beshkova
D001089:Arabinose / Q000378:metabolism; D002611:Cheese / Q000382:microbiology; D003470:Culture Media; D005285:Fermentation / Q000502:physiology; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007778:Lactobacillus / Q000378:metabolism*; D007785:Lactose / Q000378:metabolism; D008358:Mannose / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D012248:Rhodotorula / Q000378:metabolism*; D013291:Streptococcus / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism; D015014:Yogurt / Q000382:microbiology
D003470:Culture Media; D011135:Polysaccharides, Bacterial; C098632:exopolysaccharide, Streptococcus; D014994:Xylose; D001089:Arabinose; D005947:Glucose; D007785:Lactose; D008358:Mannose; D005690:Galactose