Zuzana Košťálová

Structural diversity of pectins isolated from the Styrian oil-pumpkin (Cucurbita pepo var. styriaca) fruit

To evaluate the seeded fruit biomass of the Styrian oil-pumpkin in view of its pectin component, a series of acidic polysaccharides were isolated by a six-step sequential extraction using hot water, EDTA, dilute HCl (twice) and dilute and stronger NaOH solutions. Chemical, physicochemical and spectroscopy analyses revealed that the first four fractions comprised partially methyl-esterified and acetylated pectins with varying proportions of rhamnogalacturonan regions ramified with galactose- and arabinose-containing side chains and showed considerable polymolecularity. The alkali-extracted polysaccharides contained lower amounts of pectins with homogalacturonan and arabinose-rich rhamnogalacturonan regions next to hemicelluloses prevailing in the last polysaccharide. Using (1)H-(13)C HSQC and HMBC spectroscopy, the resonances of free and methylesterified galacturonic acid residues in the purified acid-extracted pectin were unambiguously established and various diads formed by both residues identified. The results might serve as a basis for searching technological conditions to produce pectin from the oil-pumpkin fruit biomass.

Structural features of two heteroxylan polysaccharide fractions from wheat bran with anti-complementary and antioxidant activities

Wheat bran is a rich source of bioactive substances ascribed to its arabinoxylan component. Two water-soluble arabinoxylans were sequentially extracted from wheat bran. WB1, released during enzymatic digestion of starch and protein, contained medium-branched arabinoxylan (A/X=0.88) consisting of 3-O-substituted (22%), di-substituted (19.8%) and 58% unsubstituted Xylp residues. It was slightly contaminated with (1→3,1→4)-β-glucan and arabinogalactan, and free of protein. WB2 extracted with 0.5% NaOH contained ∼95% arabinoxylan (A/X=1.09). WB2 and two 5% NaOH-extracted arabinoxylans were rich in protein and phenolic compounds. All radical-scavenging assays indicated a relation with the protein and total phenolics contents. The protein-free WB1 displayed the highest hydroxyl radical scavenging effect indicating the distinct role of phenolic acids. The immunomodulatory activity of WB1 was somewhat lower, whereas, that of WB2 higher in comparison to the immunogenic polysaccharide PMII. The arabinoxylans have the potential as immuno-enhancing and antioxidant additives in functional foods.

Chemical evaluation of seeded fruit biomass of oil pumpkin (Cucurbita pepo L. var. Styriaca)

Oil pumpkin (Cucurbita pepo L. var. Styriaca) is an economically important horticultural plant cultivated for oil production. After harvesting seeds, the residual biomass has a limited application and is usually left in the field. An experimental study was performed to evaluate the chemical composition of the seeded fruit oil pumpkin biomass (OP) dried by solvent-exchange using ethanol. The sugar composition of polysaccharides obtained by sequential extraction with water and dilute alkali indicated the prevalence of pectic polysaccharides. Hemicelulloses were released in higher amounts in the alkaline step. The chemical composition of OP and its individual tissues (peel, flesh and hairy flesh) was investigated and compared to the corresponding preparations of standard pumpkin (SP, Cucurbita pepo L.). The content of components (on oven-dry basis), calculated from the analysis data of the individual tissues, was estimated for OP: 7.9 % ash, 7.6 % Klason lignin, 19.3 % pectin (as uronic acids), 34.1 % neutral carbohydrates, and 27.4 % α-cellulose and for SP: 6.4 % ash, 4.0 % Klason lignin, 20.9% pectin (as uronic acids), 38.1% neutral carbohydrates, and 29.2 % α-cellulose, respectively. The OP biomass showed a higher proportion of hemicelluloses.

Non-cellulosic polysaccharides from the leaves of small balsam (Impatiens parviflora DC.).

The leaves of the annual plant Impatiens parviflora DC., a herbal medicine in Asian countries and invasive in managed forests and natural environments in Central Europe, have the potential as a source of bioactive phenolic compounds and polysaccharides. Extractives accounted for ∼22% of the leaves, whereby, the methanolic extract contains mainly caffeic acid, ferulic acid, kaempferol, and quercetin derivatives, and 1,2,4-trihydroxynaphthalene-1-O-glucoside. From the pre-extracted leaves, non-cellulosic polysaccharides were isolated by a five-step extraction procedure using as extractants cold water, 0.05 M EDTA, and DMSO in the first three steps, and 1% and 5% NaOH in the last two steps. The isolated polysaccharide fractions were characterized by chemical, physicochemical, and spectroscopic analyses (FTIR and (1)H NMR). The first three fractions contained mainly pectin and the alkali-extracted ones methylglucuronoxylan and arabinogalactan. The suggested structural features were confirmed using HSQC NMR and COSY experiments for polysaccharides of the EDTA-fraction and the Pronase-treated 5% NaOH-fraction. The EDTA fraction comprised a pectin with low degree of methyl-esterification (DM, 37%) with few rhamnogalacturonan RG I segments bearing β-1,4-galactan as side chains. The alkali-extracted fraction comprised a degraded methylglucuronoxylan and type II 3,6-arabinogalactan in about equal amounts.

Suppressive effect of pectic polysaccharides from Cucurbita pepo L. var. Styriaca on citric acid-induced cough reflex in guinea pigs.

Several water-soluble pectic polysaccharides were isolated from the pumpkin fruit biomass and characterized by composition, structural features and molecular properties. The pectic polysaccharides were tested for antitussive activity by studying the effects of citric acid-induced cough reflex in guinea pigs and reactivity of the airway smooth muscle in vivo conditions in comparison to the narcotic drug codeine. Oral administration of all pectic polysaccharides from pumpkin inhibited the number of coughs induced by citric acid in guinea pigs, but to various extents. The results indicated that the antitussive activity of the pectic polysaccharides is affected by their molecular and structural properties, whereby a synergistic action between the polysaccharide and non-carbohydrate components on the biological response has been suggested as well. The cough depressive efficacy of most of the tested polysaccharides was comparable and even higher than that of codeine. Moreover, the application of these polysaccharides provoked any side effects what is their advantage towards the conventional opioid-derived antitussive agents.

Bioactive hemicelluloses alkali-extracted from Fallopia sachalinensis leaves

Fallopia sachalinensis, regarded as an invasive plant in Europe and designated for disposal, is traditionally used in Japan and China as herbal medicine. Attempted for valorization of the leaves, this paper reports on two protein-free polysaccharide fractions, a neutral (FS-5A) and an acidic (FS-5B) one, obtained via alkali extraction and consecutive purification. Both fractions were characterized by chemical, molecular, structural and bioactive properties. FTIR and 1D/2D NMR analyses revealed that FS-5A consisted of a fucogalactoxyloglucan, whereas, glucuronoxylan was the major hemicellulose in FS-5B accompanied with low proportions of fucosylated xyloglucan and pectic RG-I. Both hemicellulose fractions exhibited significant immunostimulating activity in the complement-fixation test and the latter had noticeable DPPH radical-scavenging ability. The results completed information about neutral and acidic bioactive polysaccharide components present in the leaves of F. sachalinensis.