Pectin preparations

Figure 3 gives an example of a typical force profile. The force is increased continuously and reaches the point - at the end of the first part of the force profile - where the pectin preparations start to flow. The so-called yield point is reached. The further increase leads to the continuous destruction of the internal structure and the proceeding shear thinning. The applied stress in part 3 of the stress profile destroys the structure of the fruit preparations completely. Now the stress is reduced linearly, see part 4 and 5, down to zero stress. The resulting flow curves 2, 3 and 4 and the enclosed calculated area from the hysteresis loop give important evidence about the time-dependent decrease of viscosity and a relative measure of its thixotropy. 

The thixotropic texture has the advantage, that the viscosity of the pectin preparations will decrease with increasing shear stress and regenerate quickly to a great extend when shear stress decreases. 

For more details about the sensory properties of the pectin preparations additional sizes such as thixotropy and viscosity have to be referred to (see figure 6). Fruit preparations with apple pectin Classic AY 901 have a relatively high yield point after shearing, a small thixotropic area, and a relatively high viscosity. This supports the statement, that their texture is weakly elastic and highly reversible. The apple pectin Classic AY 905 gives products with a sufficiently high yield point at 35 % soluble solids and a pronounced area of thixotropy. 

The gelling temperature is an important factor for the characterization and application of pectins. The pectin consumer wants a pectin fulfilling his special requirements, this can mean either working with or without pregelation. Pregelation, the weakening of gel structure, occurs when pectin preparations are stressed below their gelation temperature so that the mechanical treatment leads to an irreversible destruction of the three-dimensional network. 

The gelation processes are not solely temperature dependent but also time dependent. The determination of the setting temperature is therefore dependent on the temperature profile being used. Results can only be compared, when the pectin preparations are pretreated and measured with exactly the same parameters. 

Enzymic de-esterification of the methyl esters of pectin proceeds linearly along the chain of the molecule, giving rise to blocks of free carboxyl groups.40-44 The same conclusion was reached on the basis of the high stability-constant of calcium pectinates prepared by par-... 

Thus, by fixation of heavy metals in the alimentary tract, pectin preparations decrease the quantity of xenobiotics, which pass through the organism and are fixed in tissues. (Fig. 4)... 

Before Wofld War II attempts were made in Germany to nitrate pectins prepared by extracting sugar beet shavings. However, the properties of the nitropectins were of no great interest, and they have not found any practical application. 

Ishii, S., Kiho, K., Sugiyama, S., and Sugimoto, H. (1979). Low-methoxyl pectin prepared by pectinesterase from AspergiUus japonicus. J. Food Sci. 44 611-614. 

Kujawski, M. and Tuszynski, T. 1987. A comparison of some methods for the determination of methoxyl groups in commercial pectin preparations, Nahrung, 31(3) 233-238. 

Shkodina, O.G., Zeltser, O.A., Selivanov, N.Y. and Ignatov, V.V. 1998. Enzymic extraction of pectin preparations from pumpkin, Food Hydrocolloids, 12(3) 313—316. 

At present, a number of questions remain open. There is the specific question on the structure of the often branched side chains and the more general question on whether structural features are intra- or intermolecular phenomena. Do the molecules of a pectin preparation have smooth and hairy regions or is there a mixture of pure galac-turonan molecules and galacturonan molecules with many side chains How is the inter- and intramolecular distribution of methoxylated and free carboxyl groups ... 

Low-methoxyl pectinates precipitated by calcium were compared with like pectinates precipitated by alcohol. All the pectinates were prepared by a simultaneous acid extraction and demethylation of pectins from apple pomace at 60 C. Calcium pectinates were of higher grade but lower in yield than alcohol-precipitated pectinates prepared under comparable conditions on the basis of 65% soluble solids. Alcohol coprecipitates materials other than pectin, which act as diluents, increasing the apparent yield of the alcohol-precipitated pectinates and lowering their grades. Demethylation increased with time of treatment and acidity. The calcium-precipitated pectinates were purer, as denoted by the calcium pectate content. The calcium pectinates were studied primarily for their use in gels of low sugar content. 

In Table I, the conditions of time, temperature, pH, and yields of the calcium pectinates prepared by the simultaneous acid-extraction and demethylation of pectin from apple pomace are presented, as well as the evaluation of the acid-alcohol treated calcium pectinates as to calcium pectate content, methoxyl content (expressed on the basis of 100% calcium pectate), relative viscosity, grade, and optimum pH. These data were obtained by methods described below in the order that they appear in the table. 

Methoxyl Content. The saponification method of von Fellenberg (, ff) was used to determine the methoxyl content, and the results in Table I are expressed on the basis of 100% calcium pectate for uniformity. The methoxyl content of the calcium pectinates prepared by acid de-esterification ranged from 3.1 to 6.4% Trend curves, showing a comparison of de-esterification as denoted by the methoxyl contents of the alcohol-recovered samples and calcium-precipitated samples, are presented in Figure 2. Under comparable conditions of pH and time of treatment, the methoxyl contents of the alcohol- and the calcium-precipitated samples prepared by acid de-esterification at 60 C. were similar. 

Optimum pH of Gelation. The optimum pH of gelation for all of the acid-demethylated pectinates prepared was within a narrow range of pH 2.6 to 3.0 at... 

Pectin preparations usually show the presence of an araban and a galactan along i ith the pectic acid. By using methods that would not hydrolyze furanosidc linkings it has been possible to isolate an araban from the pectin of peanuts, apples, citnis fruits and from the seed of Lupinus albus. A galactan was also isolated from Lupinus albus. 

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