Phase changes, polysaccharides

The diversity of applications for UF in the pharmaceutical industry is unequaled in any other industry group. Concentration, purification, desalting, fractionation and sterilization are all practiced in one form or another. In some cases, the product is in the retentate in others, it is in the permeate. Occasionally, both retentate and permeate contain valuable products. The fact that all of these operations are possible with UF at ambient temperatures without phase change or addition of chemicals/solvents makes it an ideal separation tool for labile drugs and biologicals. Proteins, polysaccharides, vitamins, hormones, viruses, vaccines and antibiotics are all processed with UF. Even the water to make up these pharmaceutical solutions is often sterilized and depyrogenated by UF (see the discussion on ultrapure water in an earlier section of this chapter). 

Different polysaccharides change the perception of flavour, thus xanthan is superior to gum guar in the perception of sweetness. Mixtures of xanthan and locust bean gum have improved flavour release and texture when used in pies and pat s compared to starch. Many foods are emulsions, examples being soups, sauces and spreads. Exopolysaccharides are used to stabilise these emulsions and prevent the phases from... 

Resolution was effected by changing the polarity of the mobile phases. It is very interesting to note that the change in resolution with respect to mobile phase compositions varied from compound to compound. Resolution on polysaccharide-based CSPs in the reversed-phase mode was improved by adding cations and anions. For propranolol enantiomers on Chiralcel OD-R with sodium perchlorate salt-acetonitrile (60 40, v/v) as the mobile phase, in the presence of cations, the order of retention was Na+ > Li+ > K+ > NH4+ > N(C2H5)4+, while in the presence of anions this order was C104 > SCN- > I- > N03 > Br > Cl > AcO [90],... 

The thermally induced changes may not always be beneficial. Polysaccharide decomposition products are generally considered safe for human consumption, but traces of potentially deleterious compounds, e.g., phenol (Byrne et al., 1966) and acrolein (Walter and Fagerson, 1968), may appear. The 7-lactone of 4-hydroxy-2-pentenoic acid—a vapor-phase constituent of the pyrolysate—has been implicated in antibiosis (Oxford, 1945). 

In essence, sea urchin larval spicule formation takes place in a preformed membrane framework that continuously changes. There is, however, also an organic matrix-like framework within the spiculogenic cavity. It is composed of polysaccharides and proteins that remain insoluble after the mineral phase of the mature spicule is dissolved [75]. The framework forms concentric sheaths around the spicule long axis, and has radiating fibers that connect the sheaths laterally. It is not, however, known whether this matrix is preformed and functions as a framework to guide the mineral deposition, or whether it is deposited periodically as the mineral is introduced. 

Partitioning of volatile substances between the liquid and gas phases is mainly governed by aroma compound volatility and solubility. These physicochemical properties are expected to be influenced by wine constituents present in the medium, for instance polysaccharides, polyphenols, proteins among others. Consideration of the physicochemical interactions that occur between aroma compounds and wine constituents is necessary to understand the perception of wine aroma during consumption. The binding that occurs at a molecular level reflects changes at a macroscopic level of the thermodynamic equilibrium, such as volatility and solubility, or changes in kinetic phenomena. Thus, thermodynamic and dynamic approaches can be used to study the behaviour of aroma compounds in simple (model) or complex (foods) media. 

A newer development in ocular drug delivery systems is the use of large molecules that exhibit reversible phase transitions whereby an aqueous drop delivered to the eye reversibly gels on contact with the precorneal tear film. Such changes in viscous properties can be induced by alterations in temperature, pH, and electrolyte composition. Gelrite, a polysaccharide low-acetyl gellan gum, forms clear gels in the presence of mono- or divalent... 

---