Polysaccharides free volume

The phase separation threshold is lower for systems containing a branched polysaccharide than for systems containing a linear polysaccharide of the same molecular weight. It is higher for globular proteins compared to proteins of unfolded structure. An increase in excluded volume means a decrease in the free volume of the solution accessible for biopolymers. Thus, the excluded volume of biopolymer molecules implies that water in real foods can be nonsolvent water relative to macromolecules. 

Biopolymer incompatibility seems to provide phase-separated liquid and gel-like aqueous systems. In highly volume-occupied food systems aggregation, crystallisation and gelation of biopolymers and their adsorption at oil/water interfaces favour an increase in the free volume, which is accessible for other macromolecules. Denatura-tion of proteins during food processing decreases their solubility and co-solubility of proteins with one another and with polysaccharides and induces phase separation of the system. 

Increased moisture can plasticize a polymer matrix. Water acts not only as a solvent for small solutes but as an agent that increases the free volume of polymer molecules and their degree of segmental motion (i.e., water is differentially solvated and mobilizes parts of the heterologous structure of protein and polysaccharide polymers). When polymers, or segments within them, are given more freedom of movement, then other diffusion-based phenomena might occur more readily. Chemical reactions should not necessarily be expected to be affected by increased free volume of the polymer, and a review of the literature yields little support for this theory for most chemical reactions. Instead, some of the increased reaction rates that have been attributed to plasticization are instead the result of increased solvation. 

Xylose-rich pectic polysaccharide was extracted from defatted and protein-free cell wall preparation (5) using HCl solution (pH 1.6) at 85° C for 4 h. The extract was adjusted to pH 5.0 with ammonia, concentrated on a rotary evaporator under reduced pressure at 40°C, and precipitated with 5 volumes of 96% ethanol. After washing twice with 80% ethanol and drying in an air circulated oven at 40°C for 2 h, the pellet was ledissolved with distilled water and then precipitated with 4 vols 96% ethanol. Before the pellet was gently ground, the precipitated pellet was washed twice with 70% ethanol and dried at 40 ° in an air circulated oven for 16 h. The resultant white powder was labelled "xylose-rich pectic polysaccharide" and stored in a refrigerator. 

The solute-water interaction extends 1-3 nm (Israelachvili, 1992) and decays exponentially with distance (Van de Ven, 1989). Non-free-draining water is water within this distance traveling with the same velocity as the particle nucleus. At the interface between the non-free-draining (bound) water and the outer volume of free-draining water traveling at a different velocity, an fc [Eq. (3.27)] is generated. In this sense, hydration and the imaginary shear plane have enormous ramifications for human oral sensations elicited by dispersed polysaccharides. 

Figure 2 Typical phase diagram of an aqueous polysaccharide (l)-protein (2) dispersion showing the Gibbs free energy as a function of the volume fraction () of each, at different temperatures from Tx, where the dispersion is metastable, to the critical solution temperature (Tc), where the two components are miscible in all proportions. ABC is the spinodal curve DBE (not connected) is the binodal curve.

Insoluble laminarin (50 g.) is treated with an oxygen-free suspension of calcium hydroxide (60 g.) in 1 liter of water. After 8 days at room temperature, the suspension is filtered, and calcium is precipitated by the addition of the equivalent amount of oxalic acid. Concentration of the filtrate to a volume of 500 ml. causes precipitation of polysaccharide (21.4 g.). After filtration, and concentration to a sirup, extraction with ethanol (3 X 100 ml.) leaves further polysaccharide (7.7 g.). Evaporation of the ethanol extract affords a mixture of the sirupy D-glucometasaocharinic lactones (13.8 g.). After their conversion to the calcium salts, and crystallization from water (finally with the gradual addition of ethanol), there is obtained calcium /3 -D-glucometasao-oharinate (5.8 g.), calcium a -D-glucometasaccharinate (0.6 g.), and a residue of the mixed salts (3.7 g., principally a epimer). 

Mannitol, the most commonly employed osmotic diuretic, is a large polysaccharide molecule. It is often selected for use in the prophylaxis or treatment of oliguric ARF. It is not absorbed from the gastrointestinal tract and, therefore, is only administered i.v. with its elimination dependent on the GFR (within 30 to 60 min with normal renal function). Mannitol is distributed within the plasma and extracellular fluid spaces and produces an increase in the serum osmolality and expansion of the circulating volume. It is not generally used for the treatment of edema because any mannitol retained in the extracellular fluid can promote further edema formation. Furthermore, acute plasma volume expansion may challenge individuals with poor cardiac contractility and can precipitate pulmonary edema. Mannitol is commonly administered for the treatment of cerebral edema consequent to head trauma or to hypoxic-ischemic encephalopathy in neonatal foals. Because mannitol promotes water excretion, hypernatremia is a potential complication in patients that do not have free access to water (Martinez-Maldonado Cordova 1990, Wilcox 1991). 

A polysaccharide can be conveniently degraded for purposes of structural determinations in a rather simple way. The polysaccharide to be examined is dissolved in an excess of an oxygen-free solution of a base, usually saturated lime-water, and allowed to stand at 25-37° for several months. Cations are then removed from the solution with a suitable cation-exchange resin. Residual polysaccharide may be precipitated with three volumes of ethanol, and the degradation products separated by cellulose-column chromatography, or by fractional reprecipitation of their calcium salts. ... 

Sevag method is generally employed for the removal of free protein from the extracted mixture of polysaccharides [90,91,102]. Crude polysaccharide extract is dissolved in distilled water, and then one-fifth volume of mixmre of the reagent that consists of n-butanol and chloroform (n-butanol chloroform = 1 4, v/v) is added. The reaction mixture is shaken vigorously for 20 min and then centrifuged at 4000 rpm for 20 min [91]. The protein precipitates in the Sevag reagent in the form of a gel [90,92]. 

After extraction, hyaluronan must undergo purification as the next production operation. The extract from the animal tissue usually contains the following impurities proteins, peptides, lipids, nucleic acids, mucopolysacchrides and low molecular weight precursors. The first purification stage involves the precipitation of HA from the primary extract using ethanol or acetone or acetic acid, or a double volume of ethanol with sodium acetate at 2 °C [4]. Sometimes the dissolution-precipitation cycles are repeated several times in order to help remove low-molecular weight compounds and lipids that are soluble in acetone and ethanol. The proteins (which are free and connected with the polysaccharides) are removed... 

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