Optimum Cultivation Of A Glycolipids-producing Pseudoxanthomonas Sp. And The Study On The Composition And Surfacial Activity Of Its Metabolites

This article studied the strain SWJS T1, which was separated and preserved by the laboratory from the deep sea mud of South China Sea before, being able to produce metabolites with surfacial activity. It was identified as Pseudoxanthomonas sp. by the result of morphological observation, physiological biochemical test and 16 s rDNA sequencing and was given the name of Pseudoxanthomonas sp. SWJS T1, with a preservation number of CGMCC No.10972.The metabolite was identified as non-ionic glycolipids on the result of whole wave scanning, TLC and FT-IR. By single factor experiment and orthogonal test, the concentration of glycolipids produced by the strain SWJS T1 was increased from 0.73 mg/mL Dextrose Equivalent to 2.60 mg/mL Dextrose Equivalent, which was 2.25 times up and kept steady in 4generations of fermentation.The optimum medium is as followed. 0.50% KNO3, 2.70% glycerol, 6.30% corn oil,0.30% K2HPO4, 0.30% Na2HPO4·12H2O, 0.125% KCl, 1.5 mM Fe2(SO4)3 and 1.0 mM MgSO4. The optimum cultivation conditions are as followed. Seed age 14 h, inoculation rate4.0%, temperature 35 ℃, original pH 6.0, loading volume 50%, incubation time 87 h.Glycosyl and fatty acids accounted nearly 30% and 67% in the glycolipids, separately. As for the composition, L-fucose and glucose are the main monosaccharides, while oleic acid and linoleic acid are the main fatty acids.CMC and HLB of the glycolipids are 68 mg/L and 11.69. Surface tension of the glycolipids is slightly influenced by metal ions, and the effect of Mg2+ and Ca2+ are greater than those of Na+ and K+. The interfacial tension of glycolipids keeps steady under heating conditions. It stayed nearly the same when the solvent being heated by 60 ℃ or 90 ℃ for 30 min, or 121 ℃ for 20 min. But its tolerance to pH is comparatively weak. The glycolipids only applied to alkaline conditions and obtained the lowest interfacial tension of 4.22 mN/m at pH 8.0.Emulsibility of the glycolipids is good while the emulsion stability is bad. 0.01% dosageof the glycolipids can obtain the emulsion with the particle size distribution between 1-10 μm,while the creaming index climbed up to 31.3% after 7 d storage at room temperature.When mixed with sodium caseinate, the glycolipids could improve the emulsification by shifting the peak to the left by 1-2 μm. But the glycolipids weren’t good for the emulsion stability. After being stored at room temperature for 7 d, creaming indexes of emulsion with the mixture of the glycolipids and sodium caseinate(10%-30%) were much bigger than those of sodium caseinate only(<10%).Generally speaking, the glycolipids produced by the strain Pseudoxanthomonas sp. SWJS T1 is more suitable for being biosurfactant rather than bio-emulsifier.