Sugar rejection

Attainment of high sugar rejection at high temperature was the motlvaiton for investigating polyblend membranes. It is not difficult to obtain fructose rejections greater than 0.95 with the... 

Sugar rejection was always zero. Polyphenol rejection increased from 9% to 57% with decreasing membrane cut-off. Difference in polyphenol rejection have been observed when the must is ultr filtered in the first UF step with the BMR 100515 and after with the BMR 021006, as reported in table III. Fig.3 shows the typical behaviour of the ultrafiltrate flux observed in these experiments. A constant flux was generally obtained after two hours. Table IV shows the final must ultrafiltrate flux values. All the experiments were carried out at the same axial velocity and at the same applied pressure. Table V shows results obtained with tubular membranes (Abcor-USA). 

Table VI shows the rejection measured for total N2, polyphenols and sugars with DDS 800 and PA 300 membranes. Sugar rejections increased from about 20% with DDS 800 to 100% with PA 300. Table VII shows the rejections of various cations using the PA 300 membrane. The rejection for the majority of cations is higher than 97%. Only Cu" " and Zn" " permeate easily through the membrane. The rejections for these two cations is essentially zero. The reason is attributed to a high specific interaction of Cu and Zn with the polymeric materials forming the membranes and to Donnan equilibrium.

In order to use any of the results obtained by objective methods as the basis for the acceptance or rejection of a product, there must be available reliable information as to the relationship between the values obtained and organoleptic quality in terms of consumer acceptance and utility. Where standards are based upon measurement of such labile constituents as ascorbic acid or sugar, a knowledge of the normal values for good commercial practice is necessary. Such values have not yet been adequately established. This should constitute a useful field for research of inestimable value to the industry. 

In both their industrial and biological functions, the 3-dimensional characteristics of carbohydrates are important. Many of these stereochemical features are described for carbohydrates in the classic text by Stoddart (2). The inqportance of stereochemistry is underscored by the unique chemical and physical properties of the individual sugars, many of which are configurational isomers. Stereochemistry also plays a role in detentlining the properties of polysaccharides. Molecular shape is as significant for the properties of an industrially modified starch as it is for the recognition of one particular blood type and the rejection of others. 

The heaviest atom thus far used in structure determination of sugar derivatives is mercury in methyl 2-(chloromercuri)-2-deoxy-a-D-talopyranoside.54 A chair form of the pyranoside was the only structure that would fit the observed electron density in one projection. Several other conformations were rejected as they did not fit the results. 

Other kinetically allowed mechanistic models, i.e. hydroxide ion attack on the monoanion, can be rejected on the grounds that the required rate coefficients far exceed that found for alkaline hydrolysis of phosphate triesters. At pH > 9 two new reactions appear, one yielding a 1,6-a.nhydro sugar by nucleophilic attack through a five-membered transition state of the 1-alkoxide ion upon C-6 with expulsion of phosphate trianion. The second is apparently general-base catalysis by 1-alkoxide of water attack on C-6 or phosphorus through greater than six-membered cyclic transition states. 

Low salt rejection RO membranes (e.g., R < 0.5 for NaCl) are sometimes classified as nanoporous and allow retention of sugars and large molecules while permeating small electrolytes. In this case, a hindered transport description of the process would be appropriate with the water and nonrejected electrolytes being treated as a single fluid and the rejected sugar considered the solute. 

The HMBC also incorporates a low-pass filter that tries to reject the one-bond correlations seen in HSQC/HMQC. Low pass means that only the low values of 7ch (0-10 Hz) are allowed to pass through and produce crosspeaks in the 2D spectrum. Because there is no 13 C decoupling, the one-bond correlations appear as wide doublets (7 150 Hz) centered on the XH peak position in F2 (Fig. 11.10—squares). They obscure the weak HMBC crosspeaks and can easily be misinterpreted as long-range correlations, especially if one of the two components of the doublet happens to fall at the position of another peak in the XH spectrum. The low-pass filter is set to reject a particular 7 value, typically 135 Hz for molecules dominated by saturated hydrocarbon (e.g., 3-heptanone, menthol, cholesterol), 142 Hz for sugars, and 170 Hz for molecules dominated by aromatic carbons. The same... 

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