Pectin homogeneity

The sol-gel transition has been determined visually, with calcium and copper, for different pectins under different external conditions. As shown in Figure 5 for sample C44 the homogeneous gel phase is situated between the two transition lines. The extension of this phase was found to depend mainly on the DE, temperature and nature of the cation. With calcium the amount of cation required to get a gel increased with the degree of esterification and above 50% it became impossible to get a gel [8]. 

Marsh grapefhiit (MGF) pulp was homogenized in 5 volumes of extraction buffer at 4 C and maintained at pH 8.0 (28). The homogenate was stirred for one hour, centrifuged and the supernatant used as the PE extract. Activity was measured by titration with a Brinkman (Westbury, NY) pH stat titrator at pH 7.5 and 30°C in 25 mL of 1 % high methoxyl pectin (Citrus Colloids Limited, Hereford, UK) with O.IM NaCl. PE units are expressed as the microequivalents of ester hydrolysed per minute. Uronic acid analyses were conducted based on the m-phenyl phenol (4) as modified for microplate reading (30). 

Influence of some cations on the reaction of apple pectin with ammonia in homogeneous media... 

Acetyl esterase (AE) has been purified to homogeneity from orange peels. The purification steps included cation exchange chromatography and gel filtration. The enzyme has affinity for triacetin and sugar beet pectin with K, of 39 mM and of 26 mg/ml, respectively. AE has a MW of 42 kD and is a monomer. The isoelectric point is at pH > 9. 

The more abundant lyase produced by FORL has been purified to homogeneity as it is shown by analytical isoelectric focusing (figure 5). The data in Table 1 show that a 32.48-fold increase in specific activity is achieved with a recovery of approximately 2.36%. The enzyme showed an "endo" type of action and a great specificity for pectin. 

Among the microbial pectinesterases, the one from Coniothyrium diplodiella56 was purified by repeated chromatography on columns of Duolite A-2 and DEAE-cellulose. Two electrophoretically homogeneous forms of pectinesterase were obtained, having an identical pH optimum and the same behavior towards pectins of different d.e. 

Electrolytes affect dispersed polysaccharides through water inactivation, specific ion binding, and polyanion neutralization. Each effect is valence-dependent, but is less on neutral polysaccharides than on ionic polysaccharides. Di- and polyvalent cations gel or precipitate a constant amount of polysacchride at much lower concentrations than do monovalent cations. The precipitation reaction is used to advantage in isolating pectin with alkaline Al3+, because this cation and polymeric forms of Al(OH)3 readily precipitate and entrain pectinic acid from apple tissue homogenates. Other di- and polyvalent cation effects are crosslinking (Prud homme et al., 1989) and an increased rate of (3 elimination over monovalent cations (Sajjaanan-... 

Aspinall, G. O., and Cottrell, I. W. (1970). Lemon-peel pectin. II. Isolation of homogeneous pectins and examination of some associated polysaccharides. Can. J. Chem. 48 1283-1289. 

Figure 19.33 shows the influence of temperature and homogenization pressure on the size of protein clusters. The cluster size (< 90,3) is reduced with increasing homogenization pressure when the system was afterwards heated between 73°C and 120 C, when the heating temperature was 140°C, the cluster sizes increases dramatically. Homogenization reduces the particle size, and reduces the ratio of pectin-to-surface area ratio. Obviously, a bridging phenomenon due to the loss of pectin s capability to cover the total surface of the protein particles occurs. 

Figure 19.33. Cluster size of a milk protein pectin system processed at 73, 85, 95, 120 or 140°C and homogenization pressure between 20 and 80 MPa (Sedlmeyer et al. 2006).

Corredig, M. and Wicker, L. (2001). Changes in molecular weight distribution of three commercial pectins after valve homogenization. Food Hydrocolloids 15,17-23. 

Another possibility for simulating the fed stomach is to use a nutritional drink, like Ensure Plus (Ensure) or Nutrison (Nutricia Nordica), which has a composition that resembles a regular meal, but lacks solids. This approach has been used by Klein et al. (Klein et al., 2004), who suggested the use of Ensure Plus containing 0.45% pectin, as a viscosity enhancer, based on comparison with physicochemical parameters of a homogenized standard breakfast. 

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