Dextran impurities

Sucrose crystallizes from aqueous solutions as monoclinic, hemimor-phic crystals. The presence of raffinose or dextran impurities, if present in quantity, produces long needle-like shapes. 

Trichoderma sp. Removal of dextran impurities in sugar refining. 

Polarimetric determination of the sucrose concentration of a solution is vaUd when sucrose is the only optically active constituent of the sample. In practice, sugar solutions are almost never pure, but contain other optically active substances, most notably the products of sucrose inversion, fmctose and glucose, and sometimes also the microbial polysaccharide dextran, which is dextrorotatory. Corrections can be made for the presence of impurities, such as invert, moisture, and ash. The advantage of polarization is that it is rapid, easy, and very reproducible, having a precision of 0.001°. 

The phosphatidyl cholines PCs used in this study were obtained from the Sigma Chemical Co. The DPPC used here showed swelling behavior in CaCl2 solutions similar to that of DPPC previously obtained from other sources (I). All lipids showed less than 1% impurity by thin-layer chromatography (TLC). Water was doubly distilled and salts were of reagent grade. Dextran was obtained from Pharmacia Chemicals and mixed in known proportions with salt solutions prior to contact with lipid. 

A solvent mixture of chloroform/methanol (2 + 1 v/v) is suitable for a quantitative extraction of lipids. Addition of a small amount of BHA (cf. 3.7.3.2.2) is recommended for the stabilization of lipids against autoxidation. Nonlipid impurities were earlier removed by shaking the extracts with a special salt solution under rather demanding conditions. An improved procedure, by which emulsion formation is avoided, is based on colunm chromatography with dextran gels. 

Aqueous two-phase systems have been used as a fast and effective process for separation of biomolecules (Gupta et al, 1999). The two-phase polymer systems are commonly formed by using two incompatible polymer/poly-mer or polymer/salt systems. Poly(ethylene) glycol-dextran systems are commonly used in two-phase separation. Partitioning is a complex process and depends on the surface properties of the proteins. Depending on its hydrophilic/hydrophobic properties the target product concentrates in one of the phases, while the impurities remain in another phase and can be easily removed. The recovery of the protein from the phase-forming polymer is the main bottleneck of the purification process. 

Fig. 4. Stained filter paper sheet showing the peptide hormones oxytocin (upper) and vasopressin (lower) after separation at pH 8.5 r/2 0.1. The heavy line in the middle portion represents the position of the dextran spot. The small amount of impurity in the oxytocin is apparent. The cathode is at the left.

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