A. Oosterveld

Effect of roasting on the carbohydrate composition of Coffea arabica beans

Abstract Coffee beans (arabica) with different degrees of roast were sequentially extracted with water (90 °C, 1 h), water (170 °C, 30 min), and 0.05 M NaOH (0 °C, 1 h). The amount and composition of polysaccharides, oligosaccharides and monosaccharides in the extracts and residues were analyzed. The results were compared with the composition of the same batch of green arabica coffee beans. Although part of our results were already reported in rather fragmented studies, this study gives a more complete overview of the amount and composition of unextractable polymers, extractable polymers, oligomers, monomers, and their conversion into (non-sugar) degradation products as a function of their degree of roast. It was found that most carbohydrates in the roasted coffee bean were present as polysaccharides (extractable or unextractable). The fact that only a small part of the carbohydrates in the extracts were recovered as oligomer and even less as monomers, showed that oligomers and especially monomers were converted very rapidly into Maillard and pyrolysis products. Cellulose remains unextractable and its solubility was not affected by the degree of roast. Galactomannans were also mainly present as unextractable polymers in green beans, but were solubilized to a large extent with increasing degrees of roast. The arabinogalactans in the roasted bean were highly soluble at the extraction conditions used. The arabinose as present as side-chains in the arabinogalactans were found to be more susceptible to degradation at more severe roasting conditions than the galactans. Also evidence was found that populations of arabinogalactans with very different ara:gal ratios exist in the roasted beans as well as in the green beans.

Characterization of hop pectins shows the presence of an arabinogalactan-protein

Hop pectins were extracted from spent hops using acid extraction conditions and were characterized chemically. The acid extraction of spent hops resulted in a yield of 2%, containing 59% of polysaccharides. The hop pectins under investigation had a relatively high molecular weight and an intrinsic viscosity comparable to that of commercially available apple and citrus pectins. The low degree of methyl esterification of these pectins implicates that they are mainly suitable for use in calcium gels. The degree of acetylation and the neutral sugar content were relatively high. A high molecular weight fraction which contained arabinogalactan-proteins was shown to be present in the hop pectin extract after preparative size-exclusion chromatography. Additionally, a fraction with a lower molecular weight was present containing mainly homogalacturonans. The arabinogalactans in the high molecular weight population consisted of (1→3)- and (1→3,6)-linked galactans highly branched with arabinose and galactose side-chains. The protein part of the arabinogalactan-protein (13%) was found to be rich in cystein, threonin, serinin, alanin, and hydroxyprolin. The molecular weight distribution of the hop pectin after degradation with the enzymes endopolygalacturonase plus pectin methyl esterase suggested that the arabinogalactan-protein present in the hop pectin extract was linked to the pectin and that the arabinogalactan-protein itself had a fairly low molecular weight.

Effect of enzymatic deacetylation on gelation of sugar beet pectin in the presence of calcium

Abstract This study deals with the effect of methyl esters, acetyl groups, and neutral sugar side-chains on the gelation properties of sugar beet pectin with Ca 2+ . Sugar beet pectin was treated in the presence of Ca 2+ with the enzymes pectin methyl esterase (PE), pectin acetyl esterase (PAE), rhamnogalacturonan acetyl esterase (RGAE), arabinofuranosidase B (AF) and rhamnogalacturonase (RGase) in various combinations. Addition of RGAE plus PE or PAE plus PE to the pectin–Ca 2+ mixture significantly increased the release of acetyl groups and methyl esters, in comparison to the addition of only PE or PAE. This indicates that PE activity is hindered by the presence of acetyl groups both in the ‘smooth’ and in the `hairy’ regions. Also the PAE activity is hindered by the presence of methyl groups in the ‘smooth’ regions. Treatment with PAE plus PE led to a stiffer gel, as determined by the storage modulus ( G ′), than treatment with PE alone, while RGAE plus PE did not improve the gel forming properties. Addition of only PAE to the pectin–Ca 2+ mixture did not result in gel formation. A lower stiffness of the gel was found when RGase combined with RGAE and PE were added to the pectin–Ca 2+ mixture, in comparison to treatment with PE alone. Addition of AF plus PE to the pectin–Ca 2+ mixture gave similar rheological effects as treatment with only PE. A fraction representing the ‘smooth’ homogalacturonan regions, which was obtained after treatment of the beet pectin with RGase and subsequent size-exclusion chromatography, was also able to form a gel with Ca 2+ and PE. However, the gel formation was much slower, and the stiffness of the gel was lower than when the parental extract was used. Also with the modified pectin the treatment with PAE plus PE gave an increased stiffness of the gel in comparison to PE alone.

Oxidative cross-linking of pectic polysaccharides from sugar beet pulp.

Oxidative cross-linking of three beet pectin extracts with hydrogen peroxide/peroxidase resulted in an increase in viscosity at low concentrations and in the formation of a gel at higher concentrations. Gels were formed using concentrations of 1.5% for an autoclave preparation and one obtained by an acid extraction and of 3% for a second autoclaved extract. It was shown that in the autoclave extracts only rhamnogalacturonans and possibly the arabinans participated in the cross-linking reaction. Cross-linking of the autoclave extracts with ammonium persulfate resulted in a decrease in reduced viscosity and molecular weight, although ferulic acid dehydrodimers were formed. Treatment of the acid extracted pectin with ammonium persulfate gave a slow increase in viscosity and the formation of a high-molecular-weight population was observed. For both oxidative systems, the 8-5 dehydrodimer was predominant after cross-linking.

Enzymatic modification of pectic polysaccharides obtained from sugar beet pulp

Abstract Rhamnogalacturonans and arabinans, purified from an autoclave extract of sugar beet pulp, as well as an acid extracted beet pectin (ABP) were treated with enzymes in order to modify their physico-chemical properties. The enzymes used were arabinofuranosidase B (AF), endo-arabinanase plus arabinofuranosidase (EA+AF), rhamnogalacturonase plus rhamnogalacturonan acetyl esterase (RGase+RGAE), and polygalacturonase plus pectin methyl esterase (PG+PE). During the enzyme treatments the intrinsic viscosity ([η]w), apparent molecular weight (Mw), and radius of gyration (Rgw) of the polysaccharides were monitored. We found in most cases that treatment with glycanases decreased the [η]w of the polysaccharides investigated. However, results showed that degradation of the rhamnogalacturonan backbone of a beet pectin obtained by acid extraction had little influence on the [η]w which led to the conclusion that the rhamnogalacturonans present in this type of pectin are mainly located at the extremities of the pectin molecules. Some evidence was found that the rhamnogalacturonans obtained by autoclaving are linked through the arabinose side-chains, probably by diferulic acid cross-links. Removal of the side-chains of the arabinans present in the rhamnogalacturonans of ABPs with enzymes also showed that the arabinan side-chains contribute relatively little to the [η]w. In our experiments we found that modification with glycanases can be used to change the structural characteristics of pectic polysaccharides without a significant loss of viscosity. In this way glycanases can be used for the removal of structural elements of pectic polysaccharides, which limit their physico-chemical properties.