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Background Human health depends on a population of microorganisms that inhabit the gut and contribute to homeostasis of the host, including nutrition, immunity and metabolism. Many of the organisms are interactive and mutually dependent, where the end-products for one organism become the fuel for another through substrate and metabolic cross-feeding. To optimise the gut microbiota using diet, the composition and functionality of the gut microbiota, including these interacting networks, must be understood. Microbial composition and functionality is affected by the structure of the energy input, which is primarily dietary fibre for the gut microbiota. The structure of dietary fibre has been reviewed by carbohydrate chemists, but knowledge of how dietary fibre structure affects the gut microbiota is limited. Scope and approach The hierarchical structures of dietary fibre are reviewed, encompassing macrostructure, mesostructure and molecular structure, and how they are affected by food processing and digestion. These factors are considered in relation to their affects on microbial composition and functionality, to provide insight on the interactions between diet, the microbiota, and human health. Key findings and conclusions Food processing and digestion affect food structure, primarily through the removal of some soluble fractions and increased solubilisation of insoluble fractions. The provision of insoluble carbohydrates to the colon appears important for the sustenance of ‘keystone’ species that play a crucial role in stabilising the gut community. Further work is needed at the microbial strain level to understand the impact of increasing fibre solubility. This should be done in studies using well-characterised carbohydrates that consider the impact of food processing and digestion.

Linkage patterns and relaxation dynamics of baobab (Adansonia digitata) polysaccharides have been investigated by means of linkage analysis and rheometry. The fruit polysaccharide was mostly xylogalacturonan, with co-extracted α-glucan. The leaf polysaccharide consists predominantly of two domains, one branched at O-4 of the →2)-Rhap-(1→ residues and another branched at O-3 of the →4)-GalpA-(1→ backbone to single GlcpA-(1→ residues. Master curves of viscoelasticity of fruit polysaccharides manifested strong pH-dependency. At pH below the dissociation constant of galacturonic acid, dispersions showed liquid-like behaviour. In contrast, at neutral pH, a weak gel network formation was observed that destabilised rapidly under the influence of flow fields. The present work identifies xylogalacturonans from baobab fruit as polysaccharides with unique rheological characteristics that may point to new directions in food and pharmaceutical formulation.

Whole-transcriptome analysis was used to investigate the molecular interplay between three bacterial species that are members of the human gut microbiota. Bacteroides ovatus, Subdoligranulum variabile, and Hungatella hathewayi formed associations in cocultures fed barley β-glucan, a constituent of dietary fiber. B. ovatus depolymerized β-glucan and released, but did not utilize, 3-O-β-cellobiosyl-d-glucose (DP3) and 3-O-β-cellotriosyl-d-glucose (DP4). These oligosaccharides provided growth substrates for S. variabile and H. hathewayi with a preference for DP4 in the case of the latter species. There was increased transcription of a B. ovatus mixed-linkage-β-glucan utilization locus, as well as carbohydrate transporters in S. variabile and H. hathewayi when in batch coculture. Increased transcription of the β-glucan utilization locus did not occur in continuous culture. Evidence for interactions relating to provision of cobalamin, alterations to signaling, and modulation of the “stringent response” (an adaptation to nutrient deprivation) were detected. Overall, we established a bacterial consortium based on barley β-glucan in vitro, which can be used to investigate aspects of the functional blueprint of the human gut microbiota. IMPORTANCE The microbial community, mostly composed of bacterial species, residing in the human gut degrades and ferments polysaccharides derived from plants (dietary fiber) that would not otherwise be digested. In this way, the collective metabolic actions of community members extract additional energy from the human diet. While the variety of bacteria present in the microbial community is well known, the formation of bacterial consortia, and the consequent interactions that result in the digestion of dietary polysaccharides, has not been studied extensively. The importance of our work was the establishment, under laboratory conditions, of a consortium of gut bacteria that formed around a dietary constituent commonly present in cereals. This enabled the metabolic interplay between the bacterial species to be studied. This kind of knowledge is required to construct an interactive, metabolic blueprint of the microbial community that inhabits the human gut.

Bifidobacterial species are common inhabitants of the gut of human infants during the period when milk is a major component of the diet. Bifidobacterium breve, Bifidobacterium bifidum, Bifidobacterium longum subspecies longum, and B. longum subspecies infantis have been detected frequently in infant feces, but B. longum subsp. infantis may be disadvantaged numerically in the gut of infants in westernized countries. This may be due to the different durations of breast milk feeding in different countries. Supplementation of the infant diet or replacement of breast milk using formula feeds is common in Western countries. Formula milks often contain galacto- and/or fructo-oligosaccharides (GOS and FOS, respectively) as additives to augment the concentration of oligosaccharides in ruminant milks, but the ability of B. longum subsp. infantis to utilize these potential growth substrates when they are in competition with other bifidobacterial species is unknown. We compared the growth and oligosaccharide utilization of GOS and FOS by bifidobacterial species in pure culture and coculture. Short-chain GOS and FOS (degrees of polymerization [DP] 2 and 3) were favored growth substrates for strains of B. bifidum and B. longum subsp. longum, whereas both B. breve and B. longum subsp. infantis had the ability to utilize both short- and longer-chain GOS and FOS (DP 2 to 6). B. breve was nevertheless numerically dominant over B. longum subsp. infantis in cocultures. This was probably related to the slower use of GOS of DP 3 by B. longum subsp. infantis, indicating that the kinetics of substrate utilization is an important ecological factor in the assemblage of gut communities. IMPORTANCE The kinds of bacteria that form the collection of microbes (the microbiota) in the gut of human infants may influence health and well-being. Knowledge of how the composition of the infant diet influences the assemblage of the bacterial collection is therefore important because dietary interventions may offer opportunities to alter the microbiota with the aim of improving health. Bifidobacterium longum subspecies infantis is a well-known bacterial species, but under modern child-rearing conditions it may be disadvantaged in the gut. Modern formula milks often contain particular oligosaccharide additives that are generally considered to support bifidobacterial growth. However, studies of the ability of various bifidobacterial species to grow together in the presence of these oligosaccharides have not been conducted. These kinds of studies are essential for developing concepts of microbial ecology related to the influence of human nutrition on the development of the gut microbiota.

This study investigated the effect of puka gum (PG) (crude and purified) concentration on its emulsification properties in terms of droplet size distribution, zeta potential, rheological and microstructural properties of the emulsions and their visual phase separation. Different concentrations of PG (1–10% w/w) were used to stabilize 15% w/w soybean oil-in-water emulsions. The effect of constant shear rate and time on the apparent viscosity of PG solutions was also tested. PG stabilised-oil-in-water emulsions exhibited monomodal size distributions with average droplet sizes (d32) below 2 μm at 4% w/w PG. The apparent viscosity of these emulsions was dependent on gum concentration exhibiting a Newtonian behaviour at low PG concentrations (≤4% w/w), with shear-thinning at higher concentrations, becoming slightly more pronounced above 100s−1 and especially at 10% w/w gum. The loss modulus (G”) was higher than the storage modulus (G’) at all concentrations indicating that the liquid-like behaviour dominated at all frequencies. The apparent viscosity of PG solutions, showed an irreversible loss of viscosity after shearing over a period of time, presumably resulting from chain breakage and molecular weight reduction. PG droplets were negatively charge with zeta-potential values in the range of −30 – (−45) mV. Furthermore, PG-stabilised emulsions remained stable against phase separation for at least 30 days. Crude and purified PG exhibited no major differences in terms of their emulsifying properties at 4% w/w suggesting that a purification process may not be required for food formulations. Overall, PG can be considered as a promising natural emulsifier for emulsion-based foods and beverage products.

Polysaccharides from feijoa fruit were extracted and analyzed; the composition of these polysaccharides conforms to those typically found in the primary cell walls of eudicotyledons. The two major polysaccharide extracts consisted of mainly pectic polysaccharides and hemicellulosic polysaccharides [xyloglucan (77%) and arabinoxylan (16%)]. A collection of commensal Bacteroides species was screened for growth in culture using these polysaccharide preparations and placed into five categories based on their preference for each substrate. Most of the species tested could utilize the pectic polysaccharides, but growth on the hemicellulose was more limited. Constituent sugar and glycosyl linkage analysis showed that species that grew on the hemicellulose fraction showed differences in their preference for the two polysaccharides in this preparation. Our data demonstrate that the members of the genus Bacteroides show differential hydrolysis of pectic polysaccharides, xyloglucan, and arabinoxylan, which might influence the structure and metabolic activities of the microbiota in the human gut.

Manuka honey (MH), α-cyclodextrin (C) and a formulation containing these two components (MH + C) were subjected to simulated gastrointestinal digestion followed by fermentation with human faecal microbiota. The honey monosaccharides, glucose and fructose were 9- and 3-fold higher respectively in the digesta of MH + C compared with MH. Methylglyoxal (MGO), characteristic of MH was absent after gastric digestion. The precursor of MGO, 1,3-dihydroxyacetone was found to be at a higher concentration in MH + C, compared with MH, after digestion. The MH + C fermenta were more acidic (pH 4.6, p

Dietary fiber provides growth substrates for bacterial species that belong to the colonic microbiota of humans. The microbiota degrades and ferments substrates, producing characteristic short-chain fatty acid profiles. Dietary fiber contains plant cell wall-associated polysaccharides (hemicelluloses and pectins) that are chemically diverse in composition and structure. Thus, depending on plant sources, dietary fiber daily presents the microbiota with mixtures of plant polysaccharides of various types and complexity. We studied the extent and preferential order in which mixtures of plant polysaccharides (arabinoxylan, xyloglucan, β-glucan, and pectin) were utilized by a coculture of five bacterial species (Bacteroides ovatus, Bifidobacterium longum subspecies longum, Megasphaera elsdenii, Ruminococcus gnavus, and Veillonella parvula). These species are members of the human gut microbiota and have the biochemical capacity, collectively, to degrade and ferment the polysaccharides and produce short-chain fatty acids (SCFAs). B. ovatus utilized glycans in the order β-glucan, pectin, xyloglucan, and arabinoxylan, whereas B. longum subsp. longum utilization was in the order arabinoxylan, arabinan, pectin, and β-glucan. Propionate, as a proportion of total SCFAs, was augmented when polysaccharide mixtures contained galactan, resulting in greater succinate production by B. ovatus and conversion of succinate to propionate by V. parvula. Overall, we derived a synthetic ecological community that carries out SCFA production by the common pathways used by bacterial species for this purpose. Systems like this might be used to predict changes to the emergent properties of the gut ecosystem when diet is altered, with the aim of beneficially affecting human physiology. IMPORTANCE This study addresses the question as to how bacterial species, characteristic of the human gut microbiota, collectively utilize mixtures of plant polysaccharides such as are found in dietary fiber. Five bacterial species with the capacity to degrade polymers and/or produce acidic fermentation products detectable in human feces were used in the experiments. The bacteria showed preferential use of certain polysaccharides over others for growth, and this influenced their fermentation output qualitatively. These kinds of studies are essential in developing concepts of how the gut microbial community shares habitat resources, directly and indirectly, when presented with mixtures of polysaccharides that are found in human diets. The concepts are required in planning dietary interventions that might correct imbalances in the functioning of the human microbiota so as to support measures to reduce metabolic conditions such as obesity.

The Malvaceae family is a group of flowering plants that include approximately 244 genera, and 4225 species. Grewia mollis, and Hoheria populnea (lacebark), are examples of the Malvaceae family that are used in traditional medicine. For this study polysaccharide samples were extracted from the inner bark of Grewia mollis (unmodified (GG) and destarched grewia gum (GGDS)) and from the leaves of Hoheria populnea (lacebark polysaccharide (LB)). Wound healing properties of grewia gum and lacebark polysaccharides were investigated using 3T3 fibroblast cells cultured in supplemented DMEM. Deposition of collagen using van Gieson's stain, expression of the COL1A1 gene which encodes type I collagen using quantitative PCR, and chemotaxis using a scratch plate assay were analysed following treatment of cells with the test polysaccharides. Quantitative PCR results indicated that all three polysaccharides increased the levels of COL1A1 mRNA, with GG showing the greatest fold change. Histological staining also indicated that the fibroblasts treated with GG deposited more collagen than control cells. Additionally, scratch assay data indicated that simulated cell ‘wounds’ treated with each polysaccharide showed increased wound closure rate over a 36 h period post treatment, with GG exhibiting the greatest effect on wound closure. Analysis of the Malvaceae derived polysaccharides indicates that they could have a positive effect on mechanisms that are integral to wound healing, potentially providing greater scientific understanding behind their use in traditional medicine.

Infants fed breast milk harbor a gut microbiota in which bifidobacteria are generally predominant. The metabolic interactions of bifidobacterial species need investigation because they may offer insight into the colonization of the gut in early life. Bifidobacterium bifidum ATCC 15696 hydrolyzes 2′-O-fucosyl-lactose (2FL; a major fucosylated human milk oligosaccharide) but does not use fucose released into the culture medium. However, fucose is a growth substrate for Bifidobacterium breve 24b, and both strains utilize lactose for growth. The provision of fucose and lactose by B. bifidum (the donor) allowing the growth of B. breve (the beneficiary) conforms to the concept of syntrophy, but both strains will compete for lactose to multiply. To determine the metabolic impact of this syntrophic/competitive relationship on the donor, the transcriptomes of B. bifidum were determined and compared in steady-state monoculture and coculture using transcriptome sequencing (RNA-seq) and reverse transcription-quantitative PCR (RT-qPCR). B. bifidum genes upregulated in coculture included those encoding alpha-l-fucosidase and carbohydrate transporters and those involved in energy production and conversion. B. bifidum abundance was the same in coculture as in monoculture, but B. breve dominated the coculture numerically. Cocultures during steady-state growth in 2FL medium produced mostly acetate with little lactate (acetate:lactate molar ratio, 8:1) compared to that in monobatch cultures containing lactose (2:1), which reflected the maintenance of steady-state cells in log-phase growth. Darwinian competition is an implicit feature of bacterial communities, but syntrophy is a phenomenon putatively based on cooperation. Our results suggest that the regulation of syntrophy, in addition to competition, may shape bacterial communities. IMPORTANCE This study addresses the microbiology and function of a natural ecosystem (the infant bowel) using in vitro experimentation with bacterial cultures maintained under controlled growth and environmental conditions. We studied the growth of bifidobacteria whose nutrition centered on the hydrolysis of a human milk oligosaccharide. The results revealed responses relating to metabolism occurring in a Bifidobacterium bifidum strain when it provided nutrients that allowed the growth of Bifidobacterium breve, and so discovered biochemical features of these bifidobacteria in relation to metabolic interaction in the shared environment. These kinds of experiments are essential in developing concepts of bifidobacterial ecology that relate to the development of the gut microbiota in early life.

Members of the bacterial genus Bifidobacterium generally dominate the fecal microbiota of infants. The species Bifidobacterium longum is prevalent, but the B. longum subsp. longum and B. longum subsp. infantis strains that are known to colonize the infant bowel are not usually differentiated in microbiota investigations. These subspecies differ in their capacities to metabolize human milk oligosaccharides (HMO) and may have different ecological and symbiotic roles in humans. Quantitative PCR provides a quick analytical method by which to accurately ascertain the abundances of target species in microbiotas and microcosms. However, amplification targets in DNA extracted from samples need to be dependably differential. We evaluated the tuf gene sequence as a molecular target for quantitative PCR measurements of the abundances of B. longum subsp. infantis and B. longum subsp. longum in fecal microbiotas. This approach resulted in the detection of a tuf gene variant (operational taxonomic unit 49 [OTU49]) in Chinese infants that has sequence similarities to both B. longum subsp. infantis and B. longum subsp. longum . We compared the genome sequence and growth and transcriptional characteristics of an OTU49 isolate cultured in HMO medium to those of other B. longum subsp. infantis cultures. We concluded from these studies that OTU49 belongs to B. longum subsp. infantis , that dependable quantitative PCR (qPCR) differentiation between the B. longum subspecies cannot be achieved by targeting tuf gene sequences, and that functional genes involved in carbohydrate metabolism might be better targets because they delineate ecological functions. IMPORTANCE High-throughput DNA sequencing methods and advanced bioinformatics analysis have revealed the composition and biochemical capacities of microbial communities (microbiota and microbiome), including those that inhabit the gut of human infants. However, the microbiology and function of natural ecosystems have received little attention in recent decades, so an appreciation of the dynamics of gut microbiota interactions is lacking. With respect to infants, rapid methodologies, such as quantitative PCR, are needed to determine the prevalences and proportions of different bifidobacterial species in observational and microcosm studies in order to obtain a better understanding of the dynamics of bifidobacterial nutrition and syntrophy, knowledge that might be used to manipulate the microbiota and perhaps ensure the better health of infants.

Pseudomonas syringae pv. actinidiae is the major cause of bacterial canker and is a severe threat to kiwifruit production worldwide. Many aspects of the disease caused by P. syringae pv. actinidiae, such as the pathogenicity-relevant formation of a biofilm composed of extracellular polymeric substances (EPSs), are still unknown. Here, a highly virulent strain of P. syringae pv. actinidiae, NZ V-13, was studied with respect to biofilm formation and architecture using a flow cell system combined with confocal laser scanning microscopy. The biofilm formed by P. syringae pv. actinidiae NZ V-13 was heterogeneous, consisting of a thin cellular base layer 5 μm thick and microcolonies with irregular structures. The major component of the EPSs produced by P. syringae pv. actinidiae NZ V-13 bacteria was isolated and identified to be an exopolysaccharide. Extensive compositional and structural analysis showed that rhamnose, fucose, and glucose were the major constituents, present at a ratio of 5:1.5:2. Experimental evidence that P. syringae pv. actinidiae NZ V-13 produces two polysaccharides, a branched α- d -rhamnan with side chains of terminal α- d -Fuc f and an α- d -1,4-linked glucan, was obtained. The susceptibility of the cells in biofilms to kasugamycin and chlorine dioxide was assessed. About 64 and 73% of P. syringae pv. actinidiae NZ V-13 cells in biofilms were killed when kasugamycin and chlorine dioxide were used at 5 and 10 ppm, respectively. Kasugamycin inhibited the attachment of P. syringae pv. actinidiae NZ V-13 to solid surfaces at concentrations of 80 and 100 ppm. Kasugamycin was bacteriostatic against P. syringae pv. actinidiae NZ V-13 growth in the planktonic mode, with the MIC being 40 to 60 ppm and a bactericidal effect being found at 100 ppm. Here we studied the formation, architecture, and composition of P. syringae pv. actinidiae biofilms as well as used the biofilm as a model to assess the efficacies of bactericidal compounds.

Puka gum (PG), a high molecular weight arabinogalactan-protein (AGP) polysaccharide extracted from the native New Zealand Meryta sinclarii tree formed electrostatic complexes with whey protein isolate (WPI) under specific conditions. The PG and WPI mixtures were slowly acidified using glucono-delta-lactone (GDL), and the progressive change from soluble polymer solution to soluble complexes and to the formation of insoluble complexes (through the association of soluble complexes) were monitored using visual examination, turbidity, particle size (dynamic light scattering) and zeta-potential measurements at total biopolymer concentration C p = 0.3% w/w, protein:polysaccharide ratio Pr:Ps = 2:1, [GDL] = 0.14% w/w, and T = 20 °C. This process was characterised by identifying the phase boundaries, pH c (pH = 5.7 at which soluble complexes of WP and PG were formed) and pH Φ (pH = 4.7 at which complexes associated to form coacervates). The coacervates formed under these conditions appeared as a sticky, viscoelastic and highly extensible material. The effect of ionic strength (0–100 mM NaCl) on complex formation was also studied and a pH c /pH Φ -ionic strength phase diagram was constructed. Coacervation was fully suppressed at ionic strengths above 60 mM NaCl. Rheological measurements of the insoluble coacervate phase at different final coacervation pH (Pr:Ps = 2:1 and 4:1; C p = 3.0% w/w) showed highest complex modulus G * at approx. pH 3.6 for both Pr:Ps = 2:1 and 4:1, i.e. electrical equivalence pH (EEP), where electrostatic interactions are strongest and the overall charge on the insoluble complex is neutral.

Lactobacillus ruminis is an inhabitant of human bowels and bovine rumens. None of 10 isolates (three from bovine rumen, seven from human feces) of L. ruminis that were tested could utilize barley β-glucan for growth. Seven of the strains of L. ruminis were, however, able to utilize tetrasaccharides (3- O -β-cellotriosyl- d -glucose [LDP4] or 4- O -β-laminaribiosyl- d -cellobiose [CDP4]) present in β-glucan hydrolysates for growth. The tetrasaccharides were generated by the use of lichenase or cellulase, respectively. To learn more about the utilization of tetrasaccharides by L. ruminis , whole-transcriptome shotgun sequencing (RNA-seq) was tested as a transcriptional screen to detect altered gene expression when an autochthonous human strain (L5) was grown in medium containing CDP4. RNA-seq results were confirmed and extended by reverse transcription-quantitative PCR assays of selected genes in two upregulated operons when cells were grown as batch cultures in medium containing either CDP4 or LDP4. The cellobiose utilization operon had increased transcription, particularly in early growth phase, whereas the chemotaxis/motility operon was upregulated in late growth phase. Phenotypic changes were seen in relation to upregulation of chemotaxis/flagellar operons: flagella were rarely seen by electron microscopy on glucose-grown cells but cells cultured in tetrasaccharide medium were commonly flagellated. Chemotactic movement toward tetrasaccharides was demonstrated in capillary cultures. L. ruminis utilized 3- O -β-cellotriosyl- d -glucose released by β-glucan hydrolysis due to bowel commensal Coprococcus sp., indicating that cross feeding of tetrasaccharide between bacteria could occur. Therefore, the RNA-seq screen and subsequent experiments had utility in revealing foraging attributes of gut commensal Lactobacillus ruminis .

Gums obtained by extraction from the inner bark of stems can be found in association with starch, which must be digested in order to obtain a refined polysaccharide isolate. In the present study, grewia gum obtained from the inner bark of the stems of Grewia mollis was shown to co-exist with starch and the effect of starch digestion on the physicochemical properties of the resultant polysaccharide was evaluated.\ud \ud The gum was extracted by maceration of the inner bark in deionized water and isolated by a combination of filtration, centrifugation and finally precipitation with absolute ethanol to produce the crude grewia gum extract (GG). The presence and content of starch in the gum sample was determined followed by enzymatic digestion of the starch using α-amylase (Termamyl 120L) to give a starch-free extract (GGDS). Physicochemical properties of the extracts such as total carbohydrates, total protein, differential sugar composition, NMR, intrinsic viscosity and rheological behaviour of the samples were evaluated.\ud \ud The GG extract had total carbohydrate content of ∼ 60 % out of which 11.8 % was starch, and a protein content of 2.3 %. Samples also contained galacturonic and glucuronic acid which were highly acetylated. Both samples had a higher proportion of galacturonic acid than glucuronic acid and contained rhamnose, arabinose, galactose, glucose and xylose as neutral sugars in varying proportions. Rheological measurements on 2 %w/w dispersions of the extracts show minor differences between both the original extract and the de-starched material but were influenced by changes in pH.

It is well accepted that our gut bacteria have coevolved with us in relation to our genetics, diet and lifestyle and are integrated metabolically with us to affect our gut health adversely or beneficially. "Who is there" may vary quite widely between individuals, as might "how they do it", but "what they make" may be less variable. Many different individual species of bacteria can perform the same saccharolytic functions and so the availability of substrate (host or diet-derived) along with the degradative enzymes they possess may be key drivers of gut ecology. In this case study, we discuss detailed microbial ecology and metabolism analysis for three individuals following 48 h of in vitro faecal fermentation, using green kiwifruit as the substrate. In parallel, we have analyzed the chemical changes to the kiwifruit carbohydrates present in the fermenta to close the circle on substrate usage/degradative enzymes possessed/microbes present/microbial byproducts produced. In the absence of host carbohydrate, we see that kiwifruit carbohydrates were differentially utilized to drive microbial diversity, yet resulted in similar byproduct production. The starting ecology of each individual influenced the quantitative and qualitative microbial changes; but not necessarily the metabolic byproduct production. Thus, we propose that it is the consistent functional changes that are relevant for assessment of gut health benefits of any food. We recommend that in this era of large scale genotype/-omics studies that hypothesis-driven, bottom-up research is best placed to interpret metagenomic data in parallel with functional, phenotypic data.

Cell wall polysaccharides are resistant to digestion and absorption in the human small intestine and are considered to be delivered to the colon in a chemically unaltered state. In this paper, pulp from green and gold kiwifruit was subjected to in vitro upper-intestinal tract digestion and the chemical and physical changes to cell wall polysaccharides (dietary fibre) were investigated. Yields of insoluble fibre decreased slightly with simulated digestion while soluble fibre yields increased. Constituent sugar and glycosyl linkage analysis of the soluble and insoluble fibre fractions revealed that the chemical composition and structure of the non-starch polysaccharides remained largely unchanged. However, the degree of methylesterification of galacturonic acid residues present in the pectin-rich soluble fibre fractions of both fruit decreased with treatment; size-exclusion chromatography detected changes in the molecular weight profiles of these fractions. These changes may affect the physicochemical properties and fermentability of kiwifruit dietary fibre in the large intestine.

Fractionation of manuka, kanuka and clover honeys indicated the >10 kDa fraction contained small amounts of type II arabinogalactans (AGs), which are often present as arabinogalactan proteins (AGPs). AGPs were isolated from the >10 kDa fraction of kanuka honey using β-glucosyl Yariv reagent and their composition and structure analysed. Constituent sugar, glycosyl linkage and NMR spectroscopy analysis of the purified AGP fraction revealed a predominance of neutral sugars, mainly galactose and arabinose, linked in a highly-branched structure typical of type II AGs. The molecular weight of the major component of the purified AGPs was ∼110 kDa, as determined by size-exclusion chromatography-multi-angle laser light scattering (SEC-MALLS). The Yariv supernatant fraction contained less total sugar, especially galactose, and more protein than purified AGPs. Linkage analysis indicated this fraction also contained an AG-type polymer in addition to various other polysaccharides and SEC-MALLS indicated the molecular weight of the major component was ∼32 kDa.

The cell-wall polysaccharide components of gold kiwifruit ( Actinidia chinensis Planch. ‘Hort16A’, ZESPRI ® GOLD) have been investigated for the first time. Alcohol-insoluble residues (AIRs) were prepared from whole, unpeeled gold and green ( Actinidia deliciosa ) kiwifruit and the constituent sugar and glycosyl linkage compositions determined. AIRs from both kiwifruit contained a high proportion of cellulose; the gold kiwifruit contained a higher proportion of hemicellulosic polysaccharides and lower proportion of pectic polysaccharides compared with the green. The gold kiwifruit AIR was partitioned by sequential extraction with water, aqueous CDTA (0.05 M), aqueous Na 2 CO 3 (0.05 M) and aqueous KOH (1 M then 4 M). The glycosyl linkage compositions of each fraction were determined and the types of cell-wall polysaccharides from the gold fruit were found to be similar to those previously reported for the green fruit.

The water-soluble carbohydrates (WSCs) extracted from the underground parts (rhizome) of Arthropodium cirratum (Rengarenga lily extract); third order branches of Cordyline australis (Cabbage tree extract); a seaweed, Undaria pinnatifida (Undaria extract), and exudates from Acacia pycnantha (Acacia extract) were investigated. Extracts of Rengarenga lily, Cabbage tree, Undaria, and Acacia contained 576, 250, 275 and 794 g/kg DM WSCs, respectively. Constituent sugar analysis by gas–liquid chromatography (GLC) showed that extracts of Rengarenga lily and Cabbage tree contained predominantly fructose and glucose (82–95%). The analysis also revealed that Acacia extract contained mainly galactose (78%) and arabinose (22%) while Undaria extract, contained fucose (55%) and galactose (44%). Thin-layer chromatography (TLC) showed that, on the basis of RF values, fructan composition of Rengarenga lily extract and Cabbage tree extract was different. Cabbage tree extract contained 45% (w/w) fructans while Rengarenga lily extract contained 65% (w/w) fructans. High performance size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS) showed that the extracts had varying weight average molecular weight due to differences in the average chain length of the major carbohydrates. Data for the amino acid compositions differed considerably depending on the type of extract. Water-soluble carbohydrate extracts prepared from the four plant sources gave a wide range of WSC (250–794 g/kg DM) due to the different proportions of structural material in different species. It is not known how these differences will impact on animal production, if diets are supplemented with the extracts.

Casein-maltodextrin glyco-conjugates were prepared using an economical, food-grade process based on the Amadori re-arrangement of the Maillard reaction. The resultant glyco-conjugates were slightly yellow in colour and the degree of discolouration was dependent on heating time. Formation of glyco-conjugates was demonstrated by determining the reduction of free amino-groups by the O-phthaldialdehyde (OPA) assay and sugar reducing ends by gas chromatography-mass spectrometry (GC-MS). Increases in molecular weight were monitored by SDS-polyacrylamide gel electrophoresis (PAGE) and were in agreement with those predicted for the conjugation of casein monomers with malto-oligosaccharides of average DP 7-10. 2D-Urea-SDS-PAGE demonstrated that both protein and saccharide components co-migrate, indicating that covalent bonds were upon heating. This resulted in increases in mass-to-charge ratio of the materials, which suggested decreases in pI. These observed chemical and physical changes were reconciled with previously documented improvements in emulsifying properties. © 2004 Elsevier Ltd. All rights reserved.

The rheological properties of three xyloglucans (XGs) from the extracellular medium of suspension cultured Nicotiana plumbaginifolia cells, apple pomace and tamarind seeds, with different structural features and molecular weights have been studied. The molecular weight (weight average) of the Nicotiana , apple pomace and tamarind seed XGs determined by multi-angle laser light scattering were 129, 219 and 833 kDa, respectively. Tamarind seed XG had the highest viscosity and Nicotiana XG had the lowest viscosity, with that of apple pomace XG intermediate. The viscosity of apple pomace XG at 5% w/v was almost equivalent to that of tamarind seed XG at 2% w/v, but their behaviour at high shear rates differed; both XGs were non-Newtonian in their rheological properties, but that from tamarind seeds showed more pronounced shear-thinning. The viscosity of Nicotiana XG at 5% w/v was almost equivalent to tamarind seed XG at 0.5% w/v, displaying Newtonian behaviour. Modification of the molecular weight of the XGs and their degree of branching revealed that differences in viscosity between the molecules, and their shear-field behaviour, was due primarily to differences in molecular weight. Removal of fucose residues from apple pomace XG decreased the viscosity of solutions from 8 to 4 mPa·s, whereas removal of both fucose and galactose from apple pomace XG, resulted in precipitation from solution. Deacetylation of Nicotiana XG also resulted in precipitation from solution.

The utilisation of various prebiotic oligosaccharides by probiotic strains of Bifidobacterium lactis, Lactobacillus rhamnosus and Lactobacillus acidophilus was investigated in order to determine the synbiotic potential of various prebiotic/probiotic combinations. Analysis by HPLC and high-performance anion-exchange chromatography of the cell-free medium taken during growth of the three probiotic bacteria showed differences in the consumption of the various oligosaccharides. Analysis of galactooligosaccharides showed that both L. rhamnosus and B. lactis consumed mostly mono- and di-saccharide, while L. acidophilus consumed oligosaccharides up to trisaccharide. Both B. lactis and L. acidophilus utilised fructooligosaccharides and inulin, but showed different patterns of oligosaccharide consumption. Only L. rhamnosus grew on β-glucan oligosaccharides and preferentially consumed the trisaccharide. The results indicate the synbiotic potential of the various probiotic/prebiotic combinations, particularly L. acidophilus/galactooligosaccharides, L. acidophilus/fructooligosaccharides or inulin and L. rhamnosus/β-glucan oligosaccharides.

Cell wall polysaccharides of 'Scarlet Warren' winter squash ( Cucurbita maxima ) were investigated before and after thermal processing. Linkage analysis of polysaccharides was done by gas chromatography coupled to mass spectrometry (GC-MS). The linkage analysis showed the cell wall polysaccharide compositions of raw and cooked squash were similar. The total pectic polysaccharides (galacturonan, rhamnogalacturonan, arabinan, and arabinogalactan) contents of the cell walls of both raw and cooked squash were 39 mol %. The amounts of pectic polysaccharides and xyloglucan in the cell walls of squash showed little alteration on heating. The cellulose content of the raw and cooked cell walls was relatively high at 47 mol %, whereas the xyloglucan content was low at 4 mol %. Solid-state (13)C nuclear magnetic resonance (NMR) spectroscopy techniques were used to examine the molecular motion of the polysaccharides in the cell walls. The mobility of highly flexible galactan depends on the water content of the sample, but no difference was seen between raw and cooked samples. Likewise, the mobility of semimobile pectic polysaccharides was apparently unaltered by cooking. No change was detected in the rigid cellulose microfibrils on cooking.

Apple pomace is the press cake resulting from pressing apples for juice (see Fig. 1). This chapter is not an all-encompassing review of apple pomace, but rather highlights areas the authors view as significant and with which they have expertise. Production figures for apple pomace are shown in Table 1.

Cell walls were isolated from the mesocarp of grape (Vitis vinifera L.) berries at developmental stages from before veraison through to the final ripe berry. Fluorescence and light microscopy of intact berries revealed no measurable change in cell wall thickness as the mesocarp cells expanded in the ripening fruit. Isolated walls were analyzed for their protein contents and amino acid compositions, and for changes in the composition and solubility of constituent polysaccharides during development. Increases in protein content after veraison were accompanied by an approximate 3-fold increase in hydroxyproline content. The type I arabinogalactan content of the pectic polysaccharides decreased from approximately 20 mol % of total wall polysaccharides to about 4 mol % of wall polysaccharides during berry development. Galacturonan content increased from 26 to 41 mol % of wall polysaccharides, and the galacturonan appeared to become more soluble as ripening progressed. After an initial decrease in the degree of esterification of pectic polysaccharides, no further changes were observed nor were there large variations in cellulose (30–35 mol % of wall polysaccharides) or xyloglucan (approximately 10 mol % of wall polysaccharides) contents. Overall, the results indicate that no major changes in cell wall polysaccharide composition occurred during softening of ripening grape berries, but that significant modification of specific polysaccharide components were observed, together with large changes in protein composition.

The storage, soluble, and structural carbohydrates of two onion cultivars, the hard, pungent Pukekohe Longkeeper (PLK) and the softer, milder Houston Grano, were analyzed to determine differences that might be related to their response to sulfur nutrition received during growth as well as their postharvest attributes and end-use suitability. PLK tissue had 7 times more dry matter, composed of more fructan, sucrose, and glucose and less fructose, than Grano and a greater proportion of fructan with a degree of polymerization of 3−5. There were also differences in neutral sugar content, especially galactose, and the amount, size, and content of pectin fractions soluble in chelator and weak alkali. These two onion cultivars differed in their capacity to take up sulfur, but there was no statistical association between sulfur supply and any measured dry matter component. Keywords: Onion; texture; polysaccharide; cell wall; fructan; pectin