Breakdown Of Pectin Research Articles

Ultrastructural and cytochemical studies of fungal development and host reactions in cucumber plants infected by Pythium ultimum

Long English cucumber plants cv. Corona were inoculated with a virulent strain of Pythium ultimum, and root samples were collected at different times after inoculation for ultrastructural observations. Initial phases of infection occurred 2–7 h after inoculation. Until 48 h after inoculation, the pathogen was usually limited to the cortical area, where fungal hyphae were found to be both intercellular and intracellular. Colonization of the vascular stele occurred between 72 and 96 h after inoculation and proceeded via infection of the endodermis, the pericycle, the parenchyma cells and the vascular elements. Direct penetration of the epidermis was presumably accomplished by mechanical and enzymatic action. Hyphal penetration of host cells was usually associated with collapse of the protoplasm and disintegration of the different organelles. Aplysia gonad lectin (AGL), a polygalacturonic acid-binding lectin was used to localize pectin in Pythium-infected tisues. Cellulosic β-(1,4)-glucans were detected using an exoglucanase complexed to colloidal gold. Pectin breakdown was found to extend at a distance from the point of fungal penetration and to be associated with the release of pectin-rich fragments. By contrast, cellulose degradation was restricted to the channel of penetration without further diffusion. Some cortical and stelar cells were occluded by an amorphous electron-dense material which did not apparently contain pectic and cellulosic substances. Hyphae colonizing such reacting host cells suffered from serious damage and were prevented from further growth by the surrounding amorphous material. Other host reactions were associated with the deposition of an osmiophilic, electron-opaque material along secondary thickenings and pit cavities of xylem vessels neighbouring colonized vascular parenchyma cells, and with the occlusion of xylem elements by tyloses.

Cell Surface Interactions between Bean Leaf Cells and Colletotrichum lindemuthianum

After a brief period of biotrophic growth, the anthracnose fungus Colletotrichum lindemuthianum (Sacc. et Mgn.) Bri et Cav. develops extensively in bean leaf cells, causing severe wall alterations and death of the host protoplast. Aplysia gonad lectin, a polygalacturonic acid-binding agglutinin, was complexed to gold and used to study the extent of pectin breakdown during the necrotrophic phase of the infection process. In view of its specific binding properties for the endopolygalacturonase produced by C. lindemuthianum, a polygalacturonase-inhibiting protein isolated from bean cell walls was successfully tagged with gold particles and used for localizing the sites of enzyme accumulation in infected host tissues. The basal level of endopolygalacturonase produced by C. lindemuthianum grown in culture was found to increase severalfold when the fungus developed in host plant tissues. The enzyme was able to diffuse freely in the host cell wall, causing drastic degradation of the pectic material of primary walls and middle lamella matrices. The enzymatic alteration of plant cell walls was accompanied by the release of pectic fragments and by the accumulation of pectic molecules at specific sites, such as intercellular spaces and aggregated cytoplasm of infected host cells. The occurrence of pectic molecules at those sites where fungal growth is likely to be restricted is discussed in relation to their origin and their implication in the plant's defense system.

Review: Enzyme inactivation during heat processing of food‐stuffs

SummaryEnzyme inactivation during heat processing is reviewed with regard to fundamental aspects (structure, thermodynamics and kinetics), mathematical models and the relationship between enzyme activity and food quality. Enzyme stability is related to enzyme structure and to factors in the microenvironment. Kinetics of inactivation are categorized with respect to reaction order and two models are briefly discussed which describe the variation of inactivation rates with temperature. The determination of accurate kinetic parameters is emphasized where the objective is to develop mathematical models of enzyme inactivation in real foods. The value of modelling inactivation is assessed. Enzymes having effects on sensory quality are reviewed with particular emphasis on those enzymes which influence flavour, through lipid degradation, and those which affect texture by catalysing the breakdown of starch, pectin or protein.

Fermentation of pectin by a newly isolatedClostridium thermosaccharolyticumstrain

By enrichment on pectin a thermophilic anaerobic bacterium was isolated. This strain, identified as Clostridium thermosaccharolyticum, was capable of fast growth on pectin (μmax 0.58 h−1) forming acetate, butyrate, hydrogen, carbon dioxide, methanol and traces of ethanol. The optimum temperature for growth was 58°C and the optimal pH was 6. The initial breakdown of pectin was catalysed by methylesterase and polygalacturonate hydrolase activity; no polygalacturonate lyase activity was found.

Polysaccharide breakdown by mixed populations of human faecal bacteria

Measurements of polysaccharide-degrading activity in different fractions of human faeces showed that bacterial polysaccharidases and glycosidases were primarily associated with the washed bacterial fractions. Amylase, pectinase and xylanase were the major polysaccharide-hydrolysing enzymes detected, whilst α-L-arabinofuranosidase, β-D-xylosidase, β-D-galactosidase and β-D-glucosidase were the most active glycosidases. Starch and 3 non-starch polysaccharides (NSP; pectin, xylan and arabinogalactan) were fermented by mixed populations of human faecal bacteria in batch culture. Detailed carbohydrate analysis demonstrated that starch and pectin were the most rapidly degraded substrates and that arabinogalactan and the relatively insoluble polysaccharide xylan were broken down more slowly. Free sugars and oligosaccharides did not accumulate in culture media with any polysaccharide tested. Time-course measurements of polysaccharide remaining in the batch culture fermentations showed that the arabinose side chains of pectin, xylan and arabinogalactan were co-utilised with the backbone sugars. In these cultures, polysaccharide-degrading activity was mainly cell-associated, but extracellular polysaccharidase activity increased as the fermentations progressed. Molar ratios of acetate, propionate and butyrate produced in these experiments were dependent upon the polysaccharide substrate tested. Molar ratios of acetate, propionate and butyrate in the starch, arabinogalactan, xylan and pectin fermentations were 50:22:29, 50:42:8, 82:15:3, and 84:14:2, respectively. The presence of starch did not inhibit the breakdown of arabinogalactan, xylan or pectin by faecal bacterial, providing evidence that multicomponent substrate utilisation occurs when complex populations of faecal bacteria are provided with mixed polysaccharide substrates.

Fermentation assisted byproduct recovery in the palm oil industry

The production of palm oil from Elaeis guineensis is a leading natural product industry in Malaysia, giving rise to a number of residues, including a rich, fruity liquor from the pulp. The liquor, of which 7–10 million tonnes a year are currently produced, has some 6% organic solids, including 0·7−1·0% or more of oil which physical processing has failed to extract. Present anaerobic digestion processes exploit only the energy and fertiliser value. Methods are described in this paper for thermophilic, microbially assisted digestion for component separation and recovery, exploiting the widely used techniques for fruit juice extraction involving enzymic breakdown of starch, pectin and other cell components. Anaerobiosis and acidogenesis help protect and release residual oil, concomitantly preserving the solids against rancidity and spoilage by ensilage. The separated wet solids are nutritive (17% protein on dry matter), biologically safe and attractive to livestock. Downstream use of the liquor is aided by the thermophilic digestion.

BETWEEN‐SPECIES DIFFERENCES IN FRACTURABILITY LOSS: COMPARISON OF THE THERMAL BEHAVIOR OF PECTIC AND CELL WALL SUBSTANCES IN POTATO AND CHINESE WATERCHESTNUT1

AbstractThis study was undertaken to determine how the mode of chemical changes taking place during the cooking of two chemically similar vegetables (potato and waterchestnut) might explain the tremendous between‐species differences in cooked tissue fractura bility as determined by Instron Texture Profile Analysis. Although pectin breakdown and depolymerization by heat weakens the cell wall structure, loss of cell wall physical strength does not necessarily coincide with pectin depolymerization. Potato phosphate‐soluble pectin (PSP) showed a more rapid rate of depolymerization than waterchestnut PSP as proven by both chemical and gel chromatographic studies.The unique composition (e.g., neutral sugar content) of the cell wall microstructure of a given vegetable species is the major determinant of the resistance of that plant tissue to fracturability loss during cooking. Based on GLC analyses of cell wall components, cell wall models have been proposed to illustrate the possible structural differences between potato and waterchestnut tissue. It appears that the cell wall character of edible plant tissue for a given species is determined genetically.

Separation of Citrus Seed from Fruit Pulp for Rootstock Propagation Using a Pectolytic Enzyme1

Abstract A pectolytic enzyme facilitates the large-scale separation of citrus seed, used for rootstock propagation, from a seed-pulp mixture. The enzyme degrades the pulp via pectin breakdown that allows the seed to be collected by sieving. Seed from all citrus rootstock cultivars tested could be separated by this technique with no detrimental effect on germination.

Pectic enzymes associated with the softening of tomato fruit

Some degree of softening of maturing tomato fruit takes place before the usually accepted mechanism for the loss of firmness, involving the sequential action of pectin esterase and polygalacturonase, is operative to any extent. The possibility that pectin and pectic acid transeliminases were implicated, providing an alternative pathway for the breakdown of pectin in the tomato, was investigated. Direct spectrophotometric determination of these enzymes proved unreliable and the thiobarbituric acid test, which should give a specific colour reaction with the products, was negative. It is concluded that transeliminases do not play a significant part in the softening of tomato fruit either prior to or during ripening.

Differential induction of pectolytic enzymes of Fusarium roseum (Lk.) emend. Snyder and Hansen

Pectolytic enzymes of Fusarium roseum were differentially induced at pH 3.5 and 6.5 in solutions of specific pectic substances. Endopolygalacturonase was induced in 0.02 M mucic acid and 1% polygalacturonic acid solutions at pH 6.5 and also in a 1% pectin solution at pH 3.5. Endopolymethylgalacturonase was induced in a 1% pectin solution at pH 6.5. In addition, pectinesterase and endopectin methyl-trans-eliminase were induced in 1% pectin solutions at pH 3.5 and 6.5, respectively.Inclusion of 0.005 M CaCl2 in reaction mixtures inhibited the degradation of polygalacturonic acid by mucic and polygalacturonic acid induced polygalacturonase. In contrast, the breakdown of pectin by the pectinesterase and polygalacturonase induced in 1% pectin solutions, pH 3.5, was stimulated.

Enzymatic breakdown of pectin and acid-inhibition of the infection of Medicago roots by rhizobium

Production of a pectinase precedes infection. Acidity in the pH-range 4.5 to 5.5, which inhibits production of root-nodules by inhibiting the infection of the root-hairs, also inhibits the action of the pectinase on pectin. The enzyme's pH-requirements may determine those of nodulation.

ON THE GELATION OF PECTIN BY PLANT EXTRACTS AND ITS INHIBITION SOME CONSIDERATIONS IN RELATION TO HOSTPARASITE INTERACTIONS

Gelation of pectin by plant extracts is due to demethylation by pectin methylesterase; in the presence of Caions Ca-pectate gels are formed. Pectin methylesterase is inhibited to some extent by 1,2-dihydroxy-anthraquinone-sulphonic acid-3, 1,4-dihydroxy-anthraquinone-sulphonic acid-2, and 8-hydroxy-quinoline sulphate, but much stronger by m-digallic acid and tannic acid. A trans-eliminative breakdown of pectin can interfere with the action of pectin methylesterase. In host-parasite complexes, the degradation of pectin (either hydrolytically or trans-eliminatively) can be catalyzed by many different enzymes of plant, fungal or bacterial origin. Various substances, occurring naturally in higher plants, can greatly affect >the activity of these enzymes. Therefore, in order to obtain quantitative data on their respective activities in host-parasite systems, thorough purification of all pectolytic enzymes from such systems is indispensable.

Studies on cation-exchange capacities of roots

1. Enzymic breakdown of pectin caused an initial rapid pH drift towards the acid side when hydrogen ion-saturated roots were neutralised.

A Medium for Investigating the Breakdown of Pectin by Bacteria

DURING the course of an investigation on the bacteria associated with the rotting of potatoes in storage, carried out on behalf of the Agricultural Research Council, a large number of isolates was tested for ability to break down pectin.