Pectin is composed of a group of complex polysaccharides that are naturally found in various plants and are associated with a range of beneficial health effects. Health outcomes from dietary pectin can vary depending on botanical origin, dietary dose and structure of pectin. The objective of this scoping review is to build a comprehensive overview of the current evidence available on intervention studies conducted in humans and to better understand the possible knowledge gaps in terms of structure–function relationships across the different health-related effects. PubMed and Embase databases were searched using PRISMA-ScR guidelines, yielding 141 references (from the initial 3704), representing 134 intervention studies performed between 1961 and 2022 that met inclusion criteria. Studies were divided into six categories, which included gut health, glycaemic response and appetite, fat metabolism, bioavailability of micronutrients, immune response and other topics. Review of these human intervention studies identified a variety of cohort characteristics and populations (life stage, health status, country), sources/types of pectin (i.e. citrus, sugarbeet, apple, other and non-defined), intervention timeframes (from one single intake to 168 d) and doses (0.1–50 g/d) that were tested for health outcomes in people. Gut health, post-prandial glucose regulation and maintenance of blood cholesterol represented the largest categories of studied outcomes. Further research to strengthen the structure–function relationships for pectin with health properties and associated outcomes is warranted and will benefit from a more precise description of physico-chemical characteristics and molecular compositions, such as degree of esterification, weight, degree of branching, viscosity, gel formation and solubility.

Mucositis is an inflammation of the gastrointestinal mucosa resulting from high doses of radio/chemotherapy treatment and may lead to interruption of antineoplasic therapy. Soluble fibres, like pectin, increase SCFA production, which play a role in gut homoeostasis and inflammation suppression. Due to the properties of pectin, the aim of the present study was to evaluate the effect of a high-fibre (HF) diet on chemotherapy-induced mucositis in a murine model. C57/BL6 mice received control (AIN93M), HF, low/zero fibre (LF) diets for 10 d prior to mucositis challenging with irinotecan (75 mg/kg), or they were treated with acetate added to drinking water 5 d prior to and during the mucositis induction. Mice that received the HF diet showed decreased immune cells influx and improved histopathological parameters in the intestine, compared with mice that received the normal diet. Furthermore, the HF diet decreased intestinal permeability induced in the mucositis model when compared with the control group. This effect was not observed for acetate alone, which did not improve gut permeability. For instance, mice that received the LF diet had worsened gut permeability, compared with mice that received the normal diet and mucositis. The effects of the HF and LF diets were shown to modulate the intestinal microbiota, in which the LF diet increased the levels of Enterobacteriaceae, a group associated with gut inflammation, whereas the HF diet decreased this group and increased Lactobacillus and Bifidobacterium (SCFA producers) levels. In conclusion, the results demonstrated the importance of dietary fibre intake in the modulation of gut microbiota composition and homoeostasis maintenance during mucositis in this model.

Mauritia flexuosa palms inhabit wetland environments in the dry, seasonal Brazilian savanna (Cerrado) and produce mucilaginous secretions in the stem and petiole that have a medicinal value. The present study sought to characterize the chemical natures of those secretions and to describe the anatomical structures involved in their synthesis. Chemical analyzes of the secretions, anatomical, histochemical analyses, and electron microscopy studies were performed on the roots, stipes, petioles, and leaf blades. Stipe and petiole secretions are similar, and rich in cell wall polysaccharides and pectic compounds such as rhamnose, arabinose, xylose, mannose, galactose, and glucose, which are hydrophilic largely due to their hydroxyl and carboxylate groups. Mucilaginous secretions accumulate in the lumens of vessel elements and sclerenchyma fibers of the root, stipe, petiole, and foliar veins; their synthesis involves cell wall loosening and the activities of dictyosomes. The outer faces of the cell walls of the parenchyma tissue in the mesophyll expand to form pockets that rupture and release pectocellulose substances into the intercellular spaces. The presence of mucilage in the xylem, extending from the roots to the leaf veins and continuous with the leaf apoplast, and sub-stomatal chambers suggest a strategy for plant water economy.

The health benefits of fruit, vegetables and dietary fibre have been promoted for many years. Much of the supporting evidence is circumstantial or even contradictory and mechanisms underlying health benefits of specific foods are poorly understood. Colorectal cancer shows marked geographical differences in incidence, probably linked with diet, and explanations for this require knowledge of the complex interactions between diet, microbiota and the gut epithelium. Dietary fibres can act as prebiotics, encouraging growth of saccharolytic bacteria, but other mechanisms are also important. Some but not all soluble fibres have a ‘contrabiotic’ effect inhibiting bacterial adherence to the epithelium. This is particularly a property of pectins (galacturonans) whereas dietary fructans, previously regarded as beneficial prebiotics, can have a proinflammatory effect mediated via toxic effects of high butyrate concentrations. This also suggests that ulcerative colitis could in part result from potentially toxic faecal butyrate concentrations in the presence of a damaged mucus layer. Epithelial adherence of lectins, either dietary lectins as found in legumes, or bacterial lectins such as the galactose-binding lectin expressed by colon cancer-associated Fusobacterium nucleatum, may also be important and could be inhibitable by specific dietary glycans. Conversely, emulsifiers in processed foods may increase bacterial translocation and alter the microbiota thus promoting inflammation or cancer. Focusing on one condition is of limited value although in developing public health messages and growing evidence for impacts of dietary components on all-cause mortality is gaining more attention. We are only just starting to understand the complex interactions between food, the microbiota and health.

Whole apples are a source of pectin and polyphenols, both of which show potential to modulate postprandial lipaemia (PPL). The present study aimed to explore the effects of whole apple consumption on PPL, as a risk factor for CVD, in generally healthy but overweight and obese adults. A randomised, crossover acute meal trial was conducted with seventeen women and nine men (mean BMI of 34·1 (sem 0·2) kg/m2). Blood samples were collected for 6 h after participants consumed an oral fat tolerance test meal that provided 1 g fat/kg body weight and 1500 mg acetaminophen per meal for estimating gastric emptying, with and without three whole raw Gala apples (approximately 200 g). Plasma TAG (with peak postprandial concentration as the primary outcome), apoB48, chylomicron-rich fraction particle size and fatty acid composition, glucose, insulin and acetaminophen were analysed. Differences between with and without apples were identified by ANCOVA. Apple consumption did not alter postprandial TAG response, chylomicron properties, glucose or acetaminophen (P > 0·05), but did lead to a higher apoB48 peak concentration and exaggerated insulin between 20 and 180 min (P < 0·05). Overall, as a complex food matrix, apples did not modulate postprandial TAG when consumed with a high-fat meal in overweight and obese adults, but did stimulate insulin secretion, potentially contributing to an increased TAG-rich lipoprotein production.

The objective of the study reported in this Research Communication was to investigate the effects of pectin and whey protein concentrate (WPC) on the generation of acid whey during Greek-style yogurt (GSY) processing. Yogurt samples were prepared using pectin (0·05%, w/v) and whey protein concentrate (WPC-80) (1%, w/v) as possible ingredients that reduce the acid whey production. Control yogurt sample was prepared without addition of these ingredients. The results showed that yogurt made with pectin plus WPC had significantly higher water holding capacity (~56%) than the control (33%). Similarly, yogurt supplemented with pectin plus WPC exhibited 15% less susceptibility to syneresis compared to the control (P < 0·05). Viability of L. bulgaricus and S. thermophilus in all yogurts remained ≥7·0 and ≥8·0 log CFU/g respectively. Native PAGE analysis showed an interaction between pectin and WPC. Pectin hinders the formation of large oligomeric aggregates of whey protein which correlates with an increase in WHC and a decrease in syneresis. Our results demonstrated that a combination of pectin and WPC have the potential to limit the quantity of acid whey generation in GSY manufacturing. Thus, these ingredients have positive implications for dairy industry in the production of GSY.

The cellulose-biosynthesis inhibitor (CBI) herbicides all selectively inhibit the synthesis of cellulose despite significant chemical differences. With the exception of quinclorac, they are most effective in inhibiting cellulose synthesis in dicot plants. Dichlobenil and isoxaben are the oldest and best studied of these herbicides, whereas flupoxam is a more recent introduction and acts in many ways similarly to isoxaben. Quinclorac is unusual in that it seems to act as a cellulose inhibitor in grasses but as an auxinic herbicide in dicots. These herbicides inhibit cell plate formation at one of two relatively late stages without affecting microtubule function. The effects of dichlobenil are different from other CBI herbicides; dichlobenil inhibits cellulose synthesis but promotes callose synthesis in its place. Suspension cells of both Lycopersicon esculentum and Nicotiana tabacum can become habituated to normally inhibitory concentrations of dichlobenil or isoxaben by replacing the normal cellulose network in their walls with pectin and extensin. Natural resistance to CBI herbicides is rare and has only been found in red algae species. Arabidopsis lines produced by mutagenesis all share changes in active site rather than alterations in uptake, translocation, or metabolism of these herbicides. The lack of cross-resistance to different CBI herbicides of these mutants indicates that no fewer than three different sites in the cellulose biosynthesis pathway are affected by the different herbicides in this class.

Chronic ingestion of apple pectin has been shown to increase the absorption of quercetin in rats. The present study was designed to elucidate whether the simultaneous ingestion of quercetin with apple pectin could enhance the absorption of quercetin in humans, and the effects of dose dependency and degree of pectin methylation on quercetin absorption were also investigated. Healthy volunteers (n 19) received 200 ml of 0·5 mg/ml of quercetin drinks with or without 10 mg/ml of pectin each in a randomised cross-over design study with over 1-week intervals; urine samples from all the subjects were collected within 24 h after ingestion of the test drinks, and urinary deconjugated quercetin and its metabolites were determined using HPLC. The sum of urinary quercetin and its metabolites excreted was increased by 2·5-fold by the simultaneous ingestion of pectin. The metabolism of methylated quercetin (isorhamnetin and tamarixetin) was not affected by pectin ingestion. In six volunteers, who received quercetin drinks containing 0, 3 and 10 mg/ml of pectin, the sum of urinary quercetin and its metabolites excreted also increased in a pectin dose-dependent manner. Furthermore, the simultaneous ingestion of quercetin with low-methoxy and high-methoxy pectin, respectively, increased the sum of urinary excretion of quercetin and its metabolites by 1·69-fold and significantly by 2·13-fold compared with the ingestion of quercetin without pectin. These results elucidated that apple pectin immediately enhanced quercetin absorption in human subjects, and that its enhancing effect was dependent on the dose and degree of pectin methylation. The results also suggested that the viscosity of pectin may play a role in the enhancement of quercetin absorption.

Most plant-origin fiber sources used in pig production contains a mixture of soluble and insoluble non-starch polysaccharides (NSP). The knowledge about effects of these sources of NSP on the gut microbiota and its fermentation products is still scarce. The aim of this study was to investigate effects of feeding diets with native sources of NSP on the ileal and fecal microbial composition and the dietary impact on the concentration of short-chain fatty acids (SCFA) and lactic acid. The experiment comprised four diets and four periods in a change-over design with seven post valve t-cecum cannulated growing pigs. The four diets were balanced to be similar in NSP content and included one of four fiber sources, two diets were rich in pectins, through inclusion of chicory forage (CFO) and sugar beet pulp, and two were rich in arabinoxylan, through inclusion of wheat bran (WB) and grass meal. The gut microbial composition was assessed with terminal restriction fragment (TRF) length polymorphism and the abundance of Lactobacillus spp., Enterobacteriaceae, Bacteroides–Prevotella–Porphyromonas and the β-xylosidase gene, xynB, were assessed with quantitative PCR. The gut microbiota did not cluster based on NSP structure (arabinoxylan or pectin) rather, the effect was to a high degree ingredient specific. In pigs fed diet CFO, three TRFs related to Prevotellaceae together consisted of more than 25% of the fecal microbiota, which is about 3 to 23 times higher (P<0.05) than in pigs fed the other diets. Whereas pigs fed diet WB had about 2 to 22 times higher abundance (P<0.05) of Megasphaera elsdenii in feces and about six times higher abundance (P<0.05) of Lactobacillus reuteri in ileal digesta than pigs fed the other diets. The total amount of digested NSP (r=0.57; P=0.002), xylose (r=0.53; P=0.004) and dietary fiber (r=0.60; P=0.001) in ileal digesta were positively correlated with an increased abundance of Bacteroides–Prevotella–Porphyromonas. The effect on SCFA was correlated to specific neutral sugars where xylose increased the ileal butyric acid proportion, whereas arabinose increased the fecal butyric acid proportion. Moreover, chicory pectin increased the acetic acid proportion in both ileal digesta and feces.

The production of hydrophilic mucilages by the seed coat or pericarp, which are released upon seed hydration, is a commonly found adaptation in angiosperms, known as myxodiaspory. These are composed primarily of pectins and hemicelluloses that undergo substantive swelling upon hydration. Synthesized in the Golgi apparatus and secreted to an apoplastic space via secretory vesicles, mucilages can also contain cellulose microfibrils or cellulosic fibres that are synthesized at the plasma membrane in association with microtubules. Investigation of mucilage production in, and differentiation of, the mucilage secretory cells of the genetic model plant Arabidopsis thaliana has identified a number of regulatory genes and enzymes involved in pectin synthesis and secretion, in muro pectin modification and secondary cell wall synthesis. Studies of the role of mucilages in both a number of species and in Arabidopsis mutants affected in its production suggest that they have multiple ecological roles. These include facilitation of seed hydration, mediation of germination under waterlogged conditions, prevention of seed dispersal or predation by adherence to soil, and promotion of seed dispersal by attachment to animals. The precise role of mucilages appears to be dependent on species and their environmental context.

The present study was designed to investigate the effect of pectin on Fe bioavailability in ileorectomised rats or caecectomised rats. In Expt 1, rats were divided into the following two groups: ileorectomised rats fed a fibre-free diet (FF diet) and ileorectomised rats fed a FF diet supplemented with 5 % (w/w) pectin (pectin diet). Apparent Fe absorption in ileorectomised rats fed the pectin diet was significantly lower compared with ileorectomised rats fed the FF diet. In Expt 2, caecectomised rats and sham-operated rats were given one of the following diets for 3 weeks: diet containing ferrous iron (FeII diet), diet containing pectin at 50 g/kg diet (pectin diet) and diet containing a mixture of FeII and product prepared by the enzymatic degradation of pectin (FeII–OGA diet), which were presumed to be oligomers of galacturonic acid. The Fe content of these diets was 7·6, 8·1 and 7·7 mg/kg diet, respectively. The bioavailability of Fe in rats fed the FeII diet was not affected by caecectomy. In contrast, in rats fed the pectin diet, where Fe bound to pectin was the only Fe source, Hb gain and Hb regeneration efficiency were significantly decreased by caecectomy. The bioavailability of Fe from the FeII–OGA complex was not affected by caecectomy. These results suggest that Fe in pectin might be released by microbial degradation and subsequently made available for absorption in the large intestine, although pectin might decrease Fe absorption in the small intestine.

Eragrostis is a cosmopolitan genus of the family Poaceae. Several wild species, including E. pilosa (L.) Beauv., are harvested for food, but the only cultivated crop-species is tef [E. tef (Zucc.) Trotter]. Despite its importance as a staple food and its plasticity to diverse environmental conditions, little is known about the structural and physiological strategies that adapt tef seeds to endure diverse and variable moisture regimes. Here, we report the presence of slime cells, a type of modified epidermal cell, covering the fruit of tef and its wild relative, E. pilosa. The slime produced by Eragrostis belongs to the ‘true’ slime type, since it is exclusively composed of pectins. Pectin forms uniform layers on the cell wall inner surface, which are confined by a thin cellulose layer to prevent release into the cell lumen. In the presence of water, pectins quickly hydrate, causing swelling of the slime cells. This is followed by their detachment, which may be controlled by a thin cuticle layer on the fruit surface. The ability of slime to absorb and maintain moisture around the grain is thought to be an adaptive feature for Eragrostis growing in dry habitats. This retention of water by slime may create conditions that are suitable for rapid germination.

Prediction of carbohydrate fractions using equations from the Cornell Net Carbohydrate and Protein System (CNCPS) is a valuable tool to assess the nutritional value of forages. In this paper, these carbohydrate fractions were predicted using data from three sunflower (Helianthus annuus L.) cultivars, fresh or as silage. The CNCPS equations for fractions B2 and C include measurement of ash and protein-free neutral detergent fibre (NDF) as one of their components. However, NDF lacks pectin and other non-starch polysaccharides that are found in the cell wall (CW) matrix, so this work compared the use of a crude CW preparation instead of NDF in the CNCPS equations. There were no differences in the estimates of fractions B1 and C when CW replaced NDF; however, there were differences in fractions A and B2. Some of the CNCPS equations could be simplified when using CW instead of NDF. Notably, lignin could be expressed as a proportion of DM, rather than on the basis of ash and protein-free NDF, when predicting CNCPS fraction C. The CNCPS fraction B1 (starch + pectin) values were lower than pectin determined through wet chemistry. This finding, along with the results obtained by the substitution of CW for NDF in the CNCPS equations, suggests that pectin was not part of fraction B1 but present in fraction A. We suggest that pectin and other non-starch polysaccharides that are dissolved by the neutral detergent solution be allocated to a specific fraction (B2) and that another fraction (B3) be adopted for the digestible cell wall carbohydrates.

Methanol accumulates in maturing seeds, correlating with preharvest deterioration. Since the source of methanol may be from pectin de-methylation, methanol, cell wall uronic acid, pectin methyl esterification, pectinesterase (PE; EC 3.1.1.11) activity, and neutral sugar composition and partitioning of cell wall polysaccharides were determined during soybean (Glycine max [L.] Merrill) seed development, maturation, and desiccation in planta. Axis cell wall polysaccharides were more easily solubilized, richer in uronic acid, rhamnose, and xylose, and less rich in galactose than cotyledon cell wall polysaccharides. Methanol accumulated to 9.7 μg per two cotyledons and 0.5 μg per axis; total methanol decreased to 3 μg per two cotyledons during loss of green color. Total uronic acid increased from 0.12 to 0.27 mg per axis and 0.9 to 4 mg per cotyledon between 24 and 50 days after flowering (DAF). After loss of green color, pectin methyl esterification in axes increased from 7 to 24 mole% between 50 and 60 DAF but decreased to 14 mole%by 62 DAF in latter stages of seed desiccation. In cotyledons, methyl esterification ranged from 25 to 40 mole% and was 31 mole% after desiccation. PE activity increased 100 fold in axes, including a 30-fold increase in activity after loss of green color at 46 DAF. Cotyledon PE activity was 40-fold higher than in axes at 24 DAF, declined 75% by 56 DAF, and then increased 5 fold during desiccation. Pectin methyl de-esterification by PE is sufficient to be the sole source for methanol accumulation in seed tissues during development and maturation.

Antibodies to detect pectin in present investigations attached to distinct fibrils in vessel lumina. In carnation infected with an isolate of Fusarium oxysporum f.sp., labeling of pathogen cells also occurred; in a resistant cultivar (cv.), it was coincident with proximate pectin fibrils and linked to altered fungal walls, which was the opposite in the susceptible cv., indicating that hindrance of pathogen ability to degrade pectin may be related to resistance. Labeling of the fungus in culture was nil, except in media containing pectin, showing that pectin is not native to the pathogen. Labeling of fungal walls for cellulose in elm (inoculated with Ophiostoma novo-ulmi) and carnation also occurred, linked to adsorbed host wall components. The chitin probe often attached to dispersed matter, in vessel lumina, traceable to irregularly labeled fungal cells and host wall degradation products. With an anti-horseradish peroxidase probe, host and fungal walls were equally labeled, and with a glucosidase, differences of labeling between these walls were observed, depending on pH of the test solution. Fungal extracellular matter and filamentous structures, present in fungal walls, predominantly in another elm isolate (Phaeotheca dimorphospora), did not label with any of the probes used. However, in cultures of this fungus, extracellular material labeled, even at a distance from the colony margin, with an anti-fimbriae probe.

Dietary texture has been reported to influence parasite establishment and survival, but to what degree this relationship is modified by either the type or quantity of dietary fibre is unknown. Using a 2×4 factorial design, we explored the relationship between fibre type (soluble = pectin vs insoluble = cellulose) and fibre quantity (0, 5, 10 and 20% by dry weight) on parasitic outcomes in BALB/c mice infected with 100 Heligmosomoides polygyrus (Nematoda) larvae. Pectin, but not cellulose, exerted a significant effect on parasite egg production. Following in vitro culture of female worms, increasing levels of dietary pectin were associated with increasing release of eggs. Yet this pattern was not observed in vivo, where per capita egg production peaked at the 10% pectin concentration, but was very low in mice fed 20% pectin. Parasite establishment was elevated in mice fed 20% pectin, but was unaffected by cellulose concentration. Neither type nor quantity of fibre affected H. polygyrus survival or spatial distribution along the gastrointestinal tract. To what degree differences in parasite establishment and reproduction could be attributed to the marked effects of pectin on gut morphology (increased intestinal length, villus length, mucosa thickness and villus/crypt ratio) requires further exploration. Our data indicate that cellulose is preferable to pectin as the source of fibre for experimental diets as cellulose did not affect H. polygyrus establishment, reproduction or survival during a 4-week primary infection.

Wood degradation by the white-rot basidiomycete Meripilus giganteus (Pers.: Pers.) Karst. was studied in naturally infected and artificially inoculated wood of beech (Fagus sylvatica L.) and large-leaved lime (Tilia platyphyllos Scop.). Semi-thin sections revealed that the secondary walls of most fibres contained internal cavities. Three distinct types of cavity formation, which differed not only between hosts, but also between cell type and location in the annual ring, were identified.

Within discoloured wood of naturally infected beech, the structure of the cavities and their formation by the associated hyphae were reminiscent of a soft-rot. By contrast, cavity formation in artificially inoculated beech and large-leaved lime wood differed from a soft-rot mode of attack as extensive delignification always preceded cavity formation, and neither T-branching, L-bending, nor hyphal growth were found within cell walls. The formation of half-moon shaped cavities in beech wood was present only in tension-wood fibres. From large diameter hyphae, growing within the fibre lumen, numerous fine perforation hyphae extended transversely via helical cracks into the cell wall. Subsequent degradation of cellulose within concentric layers of the tension-wood fibres commenced from the apices of perforation hyphae.

Sections stained with ruthenium red and hydroxlamine-ferric chloride, revealed that M. giganteus preferentially degrades pectin-rich regions of the middle lamellae in xylary ray cells. In large-leaved lime, such regions were uniformly located in the middle lamellae of axial and ray parenchyma. In beech wood, degradation of pectin-rich middle lamellae regions commenced after the delignification of secondary walls and resulted in a conspicuous hollowing of multiseriate xylem rays. Plasticity in wood degradation modes by M. giganteus in large-leaved lime and beech wood reflects variations in cell wall structure and/or prevailing wood conditions.

The effect of high- (hePE) and low- (lePE) esterification pectin and high- (hvGG) and low-(lvGG) viscosity guar gum on plasma, hepatic and biliary lipids and on prevention of cholesterol gallstones was investigated in male golden Syrian hamsters (Mesocricetus auratus). Hamsters were fed on cholesterol-rich (4g/kg), gallstone-inducing diets for 6 weeks. The diets were supplemented with 80g hePE, lePE, hvGG or lvGG/kg or 80g additional cellulose/kg. No significant differences in plasma total cholesterol and triacylglycerol concentrations between hvGG and lvGG and the gallstone-inducing or cellulose-enriched diets were observed. The hePE diet produced a 16% (non-significant) reduction in total plasma cholesterol but significantly decreased the plasma triacylglycerol level by 45%. The lePE diet caused only minor changes in plasma lipids. Hepatic cholesterol concentrations were significantly higher in hamsters fed on hvGG, lvGG, hePE or lePE primarily due to the accumulation of esterified cholesterol. Supersaturated bile samples, with lithogenic indices ranging from 1.6 to 2.0, were determined with all diets. The hePE and lePE diets slightly altered the bile acid profile by increasing glycocholic acid and decreasing taurochenodeoxycholic acid concentrations resulting in a higher cholic: chenodeoxycholic acid ratio. Cholesterol gallstone formation was not substantially inhibited by the two varieties of pectin and guar gum. The hvGG, lvGG, hePE and lePE diets did not alter faecal weight and caused only minor increases in faecal bile acid excretion. In general, the present findings demonstrate that dietary pectins and guar gums had only minor effects on cholesterol metabolism and did not prevent cholesterol gallstone formation in this hamster model. Possible explanations for this lack of a distinct response to pectin and guar gum are discussed.

One-day-old broiler chickens were fed on a control diet based on maize and maize starch or diets containing 30g/kg of 89 % deacetylated chitin (chitosan) or low-methoxyl (34 % degree of esterification) pectin. Feeding of the chitosan diet to chickens significantly reduced body weights and feed intakes compared with animals fed on control or pectin diets on days 5 and 11 of the experiment. On day 12, significant reductions in total plasma cholesterol and HDL-cholesterol concentrations were observed among birds fed on the chitosan but not the pectin diet in relation to control-fed animals. A concomitant increase in the plasma HDL-cholesterol:total cholesterol ratio was observed among chitosan-fed chickens. The generally reduced concentrations of primary and total bile acids in the duodenum of birds fed on the fibre-containing diets on day 13 may have been an indication of a delay in the production and/or secretion of bile. Viscosity of the three broiler-chicken diets was measured after suspension in water, acidification and finally neutralization of the suspensions, in an attempt to simulate the effect of changes in pH and dilution of diets occurring in the gizzard and small intestine of chickens. Viscosity of the chitosan diet was significantly elevated after acidification and significantly reduced at neutralization in comparison with the control and pectin-containingdiets suggesting that the hypolipidaemic influence of chitosan observed in the present study may be due to interruption of enterohepatic bile acid circulation rather than increased viscosity in the small intestine of chickens. The low viscosity of the pectin diet in vitro together with the absence of a hypocholesterolaemic effect of this diet when fed in vivo precludes any conclusion regarding the hypocholesterolaemic mechanism of pectin observed in earlier studies.

Production of enzymes which degrade plant cell wall macromolecules has been studied in relatively few ericoid fungal isolates, although these polymers are a major component of the organic litter and an important source of nutrients for these fungi. Our aims were to investigate whether the ability to degrade the wall pectic component, only reported for one isolate, is a general feature of ericoid fungi. Of about 35 isolates from different geographic regions, all were capable of growing on pectin as the sole carbon source. Polygalacturonase (PG) activity was detected to a different degree in the culture filtrates and independently of the fungal growth rate. Solid and liquid isoelectric focusing allowed separation and identification of several polygalacturonase isoforms. Among the fungal isolates investigated, those from the northern hemisphere produced mostly acidic isoforms, whereas isolates from South Africa secreted more abundantly basic isoforms. However, purification and biochemical characterization of several PG isoforms from the different isolates revealed an optimal activity in the acidic pH range for all the PG enzymes tested. Polygalacturonase enzymes seem to be an important component of the enzymatic arsenal secreted by ericoid fungi during their saprotrophic life. In addition, they could also play a role during root colonization, since penetration across the plant cell wall is a prerequisite for the establishment of endomycorrhizal symbiosis.