Esterification, determining degree

Analytical methods. The anhydrouronic acid content (AUAC), degree of esterification (DE), degree of amidation (DA) and ash content were determined according to the methods described in Food Chemical Codex II ed [5]. 

This review will describe the analytical methods available to determine the structural components of pectin. These features determine the important physical, chemical, and biological properties of pectin. Included will be discussion of galacturonic acid determinations, degree of esterification with methyl groups, the neutral-sugar composition, and analysis of some less-common entities, such as 0-acetyl and 0-feruloyl linkages. 

The optical properties are directly related to the polymer and LC structure formation, consequently it is of paramount importance to determine the effect of side chain size and number of substituents, degree of esterification and degree of polymerization in pitch values and the optical properties of the mesophases of thermotropic liquid crystals. 

The Coloqmthoides variety of CitruIIus lanatus (an ancestor of the watermelon) is mainly grown in Eg) ) . The economic importance of this crop is owing to its seeds, and the rest of the fruit is discarded. For this reason, the waste of CitruUus lanatus var. Colocynthoides as a new source of pectin was proposed [42]. For the extraction, HCl was used at different pH values and temperatures, and it was found that at pH 2 and 85°C the highest yield of 19.75% (w/w) was reached. The degree of esterification determined was -55%. With these results, it is stated that this residue may be a potential source of pectin, but more research is needed to fully understand this source of production. 

Determining the degree of substitution using standard proton nmr refles on the integral ratio between the ceUulosic ring protons ( i 5.0-2.96) and the ester alkyl protons ( i 1.26 for butyryl and propionyl and i 2.06 for acetyl methyl groups). This simple procedure is used extensively to determine the extent of esterification and is currently the fastest, easiest way for determining the DS of mixed cellulose esters. 

Since the catalytical behaviour of titanium derivatives depends on their degree of condensation, these catalysts are used under conditions where the water concentration is very low, for instance in transesterifications or in the last steps of esterifications. However, the amounts of water required to hydrolyse these compounds are so low (less than 0.5 ppm for Ti(OBu)4) that hydrolysis is probably the determining phenomenon in most studies. It seems that before Fradet and Marshal230 the contribution of this side effect has not been taken into consideration. 

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]. 

The importance of the degree of esterification (%DE) to the gelation properties of pectins makes it desirable to obtain a fast and robust method to determine (predict) the %DE in pectin powders. Vibrational spectroscopy is a good candidate for the development of such fast methods as spectrometers and quantitative software algorithms (chemometric methods) becomes more reliable and sophisticated. Present poster is a preliminary report on the quantitative performance of different instrumentations, spectral regions, sampling techniques and software algorithms developed within the area of chemometrics. 

The degree of esterification of the methyl ester of PGA was determined acidimetrically after hydrolysing the ester with sodium hydroxide [6]. 

Methods of analysis. The polyuronic acid content (PUAC) and the degree of esterification (DE) were determined according to Owens et al (10). 

After Michaelic constant (KJ determination pectin concentration with known esterification degree was expressed in mol/M according to the content of anhydrogalacturonic acid. 

Based on the above investigations, it appears likely that prostaglandins in P. homomalla function to inhibit feeding by predatory fish. However, determination of the mechanism of their release and the degree of esterification in the ecologically active substance await further investigation. 

As is normally the case with esterification reactions, an equilibrium situation exists in this particular series, and Reaction 2, with respect to its degree of completion is dependent upon the concentration of the olefin in the reaction medium. We studied the effect of the olefin excess in the reaction on yield of ester and found that at levels less than 50%, the yields based on the acid-ester components were considerably less. With olefin excesses larger than 50%, the rate of the primary reaction, that is formation of the diester, was decreased. We therefore determined that an olefin excess of about 50% favored the primary reaction (number 2) as opposed to the secondary reaction in which the olefin can undergo polymerization in the acid media. 

With one exception [447], only sulphonated resins were used as catalysts in kinetic studies of esterification and transesterification, the resins being almost exclusively styrene—divinylbenzene copolymers in one case, a sulphonated phenol—formaldehyde resin was also used [433]. The main factors determining the catalytic activity are (i) the concentration of functional groups in protonated form (— S03H groups) and (ii) the degree of crosslinking of the copolymer (characterised by the divinylbenzene content). 

Mizote, A., Odagiri, H., Toei, K., and Tanaka, K. 1975. Determination ofcarboxylicacids(mainly galacturonic acid ) and their degree of esterification in industrial pectins by colloid titration with Cat-Floc. Analyst 100 822-826. 

Schultz, T.H. 1965b. Determination of the degree of esterification of pectin. In Methods in Carbohydrate Chemistry, Vol. 5 (R.L. Whistler, ed.) pp. 189-194. Academic Press, New York. 

Equations (2.13) and (2.14) (Table 2.4) describe the synthesis of UP oligomers. This is usually carried out in bulk at elevated temperatures. During a first step, the temperature is kept in the range of 60-130°C and is increased up to 160-220°C in a second step. During this second step most of the maleate groups (cis isomer) are isomerized into fumarate groups (trans isomer), Eq. (2.15) (Table 2.4). The degree of isomerization is determined by the esterification conditions (temperature, acid content, catalyst, nature of the diol). It must be carefully controlled because the content of fumarate units determines many properties of UP networks. 

N. O. Maness, J. D. Ryan, and A. J. Mort, Determination of the degree of methyl esterification of pectins in small samples by selective reduction of esterified galacturonic acid to galactose, Anal. Biochem., 185 (1990) 346-352. 

---