Antilisterial activity of grape juice and grape extracts derived from Vitis vinifera variety Ribier.

Grape juice and skin and seed extracts of Vitis vinifera var. Ribier black table grapes were found to be highly inhibitory towards Listeria monocytogenes. This grape juice was also active against all other Listeria species tested but not against Bacillus cereus, Salmonella Menston, Escherichia coli, Staphylococcus aureus or Yersinia enterocolitica. Fractionation of the extracts showed that the antilisterial activity was strongest in the polymeric phenolic fractions. Two different types of active compounds were identified: the red-pigmented polymeric phenolics from juice and skin showed pH-dependent antilisterial activity, while the unpigmented polymeric phenolics from the seed showed antilisterial activity which was independent of pH.

Green tea catechins partially protect DNA from (.)OH radical-induced strand breaks and base damage through fast chemical repair of DNA radicals.

The catechins, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG) and (-)-epigallocatechin gallate (EGCG) are believed to be active constituents of green tea accounting for the reported chemoprevention of certain cancers. The molecular mechanisms by which the measured low concentrations (ca. micromolar) of catechins in humans can reduce the incidence of carcinogenesis is not clear. Using an in vitro plasmid DNA system and radiolytically generating reactive oxygen species (ROS) under constant scavenging conditions, we have shown that all four catechins, when present at low concentrations, ameliorate free radical damage sustained by DNA. A reduction in both prompt DNA single-strand breaks and residual damage to the DNA bases, detected by subsequent incubation with the DNA glycosylases formamidopyrimidine (FPG), endonuclease III (EndoIII) and 5' AP endonuclease exonuclease III (ExoIII), was observed. EGCG was found to be the most active of the catechins, with effects seen at micromolar concentrations. Combined fast-reaction chemistry studies support a mechanism of electron transfer (or H-atom transfer) from catechins to ROS-induced radical sites on the DNA. These results support an antioxidant role for catechins in their direct interaction with DNA radicals.

Oligosaccharides related to xyloglucan: synthesis and X-ray crystal structure of methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-alpha-D-x ylopyranoside and the synthesis of methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-beta-D-xy lopyranoside.

Trisaccharides, methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-alpha-D-xy lopyranoside and methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-beta-D-xyl opyranoside, which are related to the side chain of xyloglucan have been synthesised. The beta-galactopyranosyl linkage of each was constructed using silver trifluoromethanesulfonate-promoted glycosylations of 2-O-acetyl-3,4,6-tri-O-benzyl-beta-D-galactopyranosyl chloride and the corresponding anomer of methyl 3,4-tri-O-benzyl-D-xylopyranoside. The resulting disaccharides were deacetylated and fucosylated using assisted halide reactions with tri-O-benzyl-alpha-L-fucopyranosyl bromide. Hydrogenolytic debenzylation of the resulting protected trisaccharides gave the methyl glycosides of the fucose-containing xyloglucan side chain. The structure of methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-alpha-D-xy lopyranoside as the monohydrate was confirmed by an X-ray crystallographic study.

Celery (Apium graveolens L.) parenchyma cell walls examined by atomic force microscopy: effect of dehydration on cellulose microfibrils.

Atomic force microscopy (AFM) was used to image celery (Apium graveolens L.) parenchyma cell walls in situ. Cellulose microfibrils could clearly be distinguished in topographic images of the cell wall. The microfibrils of the hydrated walls appeared smaller, more uniformly distributed, and less enmeshed than those of dried peels. In material that was kept hydrated at all times and imaged under water, the microfibril diameter was mainly in the range 6-25 nm. The cellulose microfibril diameters were highly dependent on the water content of the specimen. As the water content was decreased, by mixing ethanol with the bathing solution, the microfibril diameters increased. Upon complete dehydration of the specimen we observed a significant increase in microfibril diameter. The procedure used to dehydrate the parenchyma cells also influenced the size of cellulose microfibrils with freeze-dried material having larger diameters than air-dried material.

Oligosaccharides related to xyloglucan: synthesis and X-ray crystal structure of methyl 2-0-(alpha-L-fucopyranosyl)-beta-D-galactopyranoside.

The disaccharides methyl 2-O-(alpha-L-fucopyranosyl)-beta-D-galactopyranoside and methyl 2-O-(alpha-L-fucopyranosyl)-alpha-D-galactopyranoside have been synthesised using the assisted halide reaction of tri-O-benzyl-alpha-L-fucopyranosyl bromide with methyl 3,4,6-tri-O-benzyl-beta-D-galactopyranoside and methyl 3,4,6-tri-O-benzyl-alpha-D-galactopyranoside to construct the interresidue glycosidic linkages. A crystal structure of methyl 2-O-(alpha-L-fucopyranosyl)-beta-D-galactopyranoside was determined using Mo-K alpha X-ray data at 183 K. The space group is P1 (No. 1) with the unit cell containing two molecules of the disaccharide with unique conformations and a water molecule. The structure was refined to R = 0.0566 for 2969 reflections. The L-fucopyranosyl and D-galactopyranosyl residues have the nominal 1C4 and 4C1 conformations, respectively. The interresidue torsion angles are comparable with those generated in a recent molecular modelling study.

Cell Wall Changes in Nectarines (Prunus persica) : Solubilization and Depolymerization of Pectic and Neutral Polymers during Ripening and in Mealy Fruit.

Nectarine fruit (Prunus persica L. Batsch var nectarina [Ait] maxim) cultivar Fantasia were either ripened immediately after harvest at 20 degrees C or stored for 5 weeks at 2 degrees C prior to ripening. Fruit ripened after 5 weeks of storage did not soften to the same extent as normally ripened fruit, they lacked juice, and had a dry, mealy texture. Pectic and hemicellulosic polysaccharides were solubilized from the mesocarp of the fruit using phenol:acetic acid:water (PAW) treatment to yield PAW-soluble material and cell wall material (CWM). The carbohydrate composition and relative molecular weight (M(r)) of polysaccharide fractions released from the CWM by sequential treatment with cyclohexane-trans-1,2-diamine tetra-acetate, 0.05 m Na(2)CO(3), 6 m guanidinium thiocyanate, and 4 m KOH were determined. Normal ripening of nectarines resulted in solubilization of pectic polymers of high M(r) from CWM during the first 2 d at ripening temperatures. Concurrently, galactan side chains were removed from pectic polymers. Solubilized pectic polymers were depolymerized to lower M(r) species during the latter stages of ripening. Upon removal from cool storage, fruit had undergone some pectic polymer solubilization, and after ripening, pectins were not depolymerized and were of high M(r). Side chains did not appear to be removed from insoluble pectic polymers and branched pectins accumulated in the CWM. The molecular weight profiles obtained by gel filtration of the hemicellulosic fractions from normally ripening and mealy fruit were similar. The results suggest that mealiness results as a consequence of altered pectic polymer breakdown, including that associated with neutral side chains.

Cell Wall Dissolution in Ripening Kiwifruit (Actinidia deliciosa) : Solubilization of the Pectic Polymers.

Pectic polysaccharides solubilized in vivo during ripening, were isolated using phenol, acetic acid, and water (PAW) from the outer pericarp of kiwifruit (Actinidia deliciosa [A. Chev.] C.F. Liang and A.R. Ferguson var deliciosa ;Hayward') before and after postharvest ethylene treatment. Insoluble polysaccharides of the cell wall materials (CWMs) were solubilized in vitro by chemical extraction with 0.05 molar cyclohexane-trans-1,2-diamine tetraacetate (CDTA), 0.05 molar Na(2)CO(3), 6 molar guanidinium thiocyanate, and 4 molar KOH. The Na(2)CO(3)-soluble fraction decreased by 26%, and the CDTA-soluble fraction increased by 54% 1 day after ethylene treatment. Concomitantly, an increase in the pectic polymer content of the PAW-soluble fraction occurred without loss of galactose from the cell wall. The molecular weight of the PAW-soluble pectic fraction 1 day after ethylene treatment was similar to that of the Na(2)CO(3)-soluble fraction before ethylene treatment. Four days after ethylene treatment, 60% of cell wall polyuronide was solubilized, and 50% of the galactose was lost from the CWM, but the degree of galactosylation and molecular weight of pectic polymers remaining in the CWMs did not decrease. The exception was the CDTA-soluble fraction which showed an apparent decrease in molecular weight during ripening. Concurrently, the PAW-soluble pectic fraction showed a 20-fold reduction in molecular weight. The results suggest that considerable solubilization of the pectic polymers occurred during ripening without changes to their primary structure or degree of polymerization. Following solubilization, the polymers then became susceptible to depolymerization and degalactosidation. Pectolytic enzymes such as endopolygalacturonase and beta-galactosidase were therefore implicated in the degradation of solubilized cell wall pectic polymers but not the initial solubilization of the bulk of the pectic polymers in vivo.

Concentration of sugars in commercial infant foods in New Zealand.

Concern has been expressed about the level of sugars in baby foods. It has been suggested that high levels of sucrose consumption during infancy and early childhood have been related not only to direct deleterious effects on health and teeth but also to the acquisition of taste patterns which lead to established sweet preferences in later life. This study was undertaken to determine the sugar content of a variety of commercially available New Zealand infant food using the para-hydroxybenzoic acid hydrazide colorimetric reaction. Twenty-eight different foods were assayed, and five baby desserts studied in detail. All infant desserts contained sucrose. Estimates of the total sugar content of desserts ranged from 16 to 47 percent. Sucrose levels varied from less than 1, to 23 percent. The level of sugars in commercial baby foods appeared unnecessarily high. It is suggested that New Zealand manufacturers seriously examine the need to add sucrose to such products.