Extraction and characterisation of very highly methylated pectins from lemon cell walls

Anti-respiratory syncytial virus and anti-herpes simplex virus activity of six Tanzanian medicinal plants with extended studies of Erythrina abyssinica stem bark

ETHNOPHARMACOLOGICAL RELEVANCE

Except for few highly pathogenic viruses, no antiviral drug has been approved for treatment of viral infections in humans. Plant extracts, selected based on their ethno-medical use, represent an important source of compounds for the development of novel candidate antiviral drugs. This especially concerns plants with ethnomedical records on their use in treatment of viral infections.

AIM OF THE STUDY

To identify and document medicinal plants used by traditional health practitioners (THPs) for treatment of respiratory infections and muco-cutaneous lesions in order to study their antiviral activity including identification of active components and elucidation of mode of antiviral activity.

MATERIALS AND METHODS

The ethno-medical survey was performed in the Kagera region of Tanzania. The THPs were asked for plants used for treatment of signs and symptoms of respiratory infections and watery muco-cutaneous blisters in oral and genital regions. The plants identified were successively extracted with n-hexane, ethyl acetate and water, and the extracts assayed for anti-respiratory syncytial virus (RSV), anti-herpes simplex virus 2 (HSV-2), and anti-human parainfluenza virus 2 (HPIV-2) activity in cultured cells. Antiviral components were separated by ethanol precipitation and CL-6B chromatography, and the mode of antiviral activity elucidated by the time-of-addition assay and selection for the virus variants resistant to antiviral plant extract.

RESULTS

THPs identified fifteen plants used for treatment of respiratory infections and muco-cutaneous blisters. The water extract, but not n-hexane or ethyl acetate extracts, of six of these plants including Erythrina abyssinica stem bark, inhibited infectivity of two glycosaminoglycan-binding viruses i.e., RSV and HSV-2 but not the sialic acid binding HPIV-2. An activity-guided separation revealed that antiviral component(s) of water extract of E. abyssinica could be precipitated with ethanol. This sample potently and selectively inhibited RSV and HSV-2 infectivity in cultured cells with IC50 values of 2.1 μg/ml (selectivity index >476) and 0.14 μg/ml (selectivity index >7143) respectively. The sample exhibited inhibitory effect on the virus attachment to and entry into the cells by directly targeting the viral particles. Indeed, 10 consecutive virus passages in HEp-2 cells in the presence of this extract selected for a resistant RSV variant lacking the attachment, viral membrane-associated, G protein due to a stop codon at amino acid residue 33 (Leu33stop). Fractionation of the E. abyssinica extract on a CL-6B column revealed that anti-RSV and HSV-2 activity correlated with carbohydrate content. The most pronounced antiviral activity was associated with a carbohydrate containing ingredient of molecular mass of <5 kDa, which may polymerize to antiviral composites of up to 410 kDa.

CONCLUSIONS

Altogether, the water extract of six medicinal plants showed anti-RSV and anti-HSV-2 activities. Extended studies of the stem bark of E. abyssinica identified antiviral components that potently and selectively inhibited infectivity of free RSV and HSV-2 particles, a feature of importance in topical treatment of these infections. This observation confirms ethno-medical information concerning the use of E. abyssinica extract for treatment of respiratory infections and herpetic lesions.

The Influence of Extrusion Processing on the Gelation Properties of Apple Pomace Dispersions: Involved Cell Wall Components and Their Gelation Kinetics

By-products of fruits and vegetables like apple pomace can serve as techno-functional ingredients in foods. Due to their physicochemical properties, e.g., viscosity, water absorption, or oil-binding, food by-products can modify the texture and sensory perception of products like yogurts and baked goods. It is known that, by extrusion processing, the properties of by-products can be altered. For example, by thermo-mechanical treatment, the capacity of food by-products to increase viscosity is improved. However, the mechanism and involved components leading to the viscosity increase are unknown. Therefore, the complex viscosity of apple pomace dispersions and the involved fractions as pectin (a major part of the water-soluble fraction), water-soluble and water-insoluble fraction, were measured. In the investigated range, an increase in the pectin yield and water solubility was observed with increasing thermo-mechanical treatment by extrusion processing. However, pectin and water-soluble cell wall components had only a limited effect on the complex viscosity of apple pomace dispersions. The insoluble fraction (particles) were investigated regarding their swelling behavior and influence on the complex viscosity. An intensification of thermo-mechanical treatment resulted in increasing swelling behavior.

Extrusion and Extruded Products: Changes in Quality Attributes as Affected by Extrusion Process Parameters: A Review

Extrusion of foods is an emerging technology for the food industries to process and market a large number of products of varying size, shape, texture, and taste. Extrusion cooking technology has led to production of wide variety of products like pasta, breakfast cereals, bread crumbs, biscuits, crackers, croutons, baby foods, snack foods, confectionery items, chewing gum, texturized vegetable protein (TVP), modified starch, pet foods, dried soups, dry beverage mixes etc. The functional properties of extruded foods plays an important role for their acceptability which include water absorption, water solubility, oil absorption indexes, expansion index, bulk density and viscosity of the dough. The aim of this review is to give the detailed outlines about the potential of extrusion technology in development of different types of products and the role of extrusion-operating conditions and their effect on product development resulting in quality changes i.e physical, chemical, and nutritional, experienced during the extrusion process.

Characterisation of cell-wall polysaccharides from mandarin segment membranes

In an attempt to develop a process of enzymatic peeling of mandarin segments suitable for use on an industrial scale, the cell wall fraction of the segment membrane of Satsuma mandarin fruits was extracted to obtain a chelating agent-soluble pectin fraction (ChSS), a dilute sodium hydroxide-soluble pectin fraction (DASS), a 1M sodium hydroxide-soluble hemicellulose fraction (1MASS), a 4M sodium hydroxide-soluble hemicellulose fraction (4MASS) and a cellulose-rich residue (3.1, 0.9, 0.4, 0.7 and 1.6%w/w of fresh membrane, respectively). The ChSS pectin consisted mainly of galacturonic acid followed by arabinose and galactose. The DASS fraction contained less galacturonic acid and more neutral sugars than ChSS. Eighty-nine percent of the galacturonic acid present in the segment membranes was recovered in the above two pectin fractions. The two hemicellulosic fractions consisted of two different molecular weight populations, which also differed in their sugar composition. Arabinose, xylose, mannose, galactose and glucose were the main sugar constituents of these hemicellulose fractions. In addition to an (arabino)xylan and a xyloglucan, the presence of an arabinogalactan is suggested by the sugar composition of both hemicelluloses. The pectin fractions were also characterised by their degradability by the pectic enzymes polygalacturonase, pectinmethylesterase and rhamnogalacturonan hydrolase. However the degree of degradation of the pectin fractions by enzymes differed, and the amount of the polymeric materials resistant to further degradation and the oligomeric products also differed. Using pectic enzymes it is possible to obtain peeled mandarin segments ready to eat or for canning.

Faba bean hulls as a potential source of pectin

This study aimed for the first time to assess the potential use of faba bean hulls as a source of pectin. The study involved extracting pectin under various conditions of pH, temperature and extraction time and determining how these conditions affected pectin yield and its characteristics. The maximum yield of extracted pectin did not coincide with the highest degree of esterification since the maximum yield (15.75 %) was recorded at pH 1.5 and at a temperature of 85 °C for an 80-min extraction period and solid to liquid (1: 25) ratio, while the highest degree of esterification (54.62 %) occurred at pH 2.5 and at temperature of 90 °C for a 60-min extraction period. The composition of the pectin varied according to the extraction conditions: the neutral sugars galactose, arabinose and rhamnose increased under milder extraction conditions while glucose, mannose and xylose sugars predominated under harsher extraction conditions. The results indicated that faba bean hulls contains adequate amount of pectin, suitable for commercial utilization.

Extrusion-induced changes to the chemical profile and viscosity generating properties of citrus fiber

Each of 8 variants in extrusion conditions was applied to a commercially available citrus fiber. Extrusion under conditions where the specific mechanical energy (SME) exceeded 400 kJ·kg(-1) was able to solubilize up to 30% of the fibers. Where the SME was ∼200 kJ·kg(-1) the degree of fiber solubilization was between 8 and 12%. All extruded fibers showed a loss of water-retaining capacity compared to the reference fiber, and this was attributed to the disruption of the integrated cell wall structure during the extrusion process. Nevertheless, within the 8 extruded variants there was a wide range of viscosity generating capacity which depended on the level of SME to which the fibers were subjected. The SME also had a pronounced effect on the nature of the solubilized fibers in terms of both their monosaccharide composition and their molecular weight profile. Both pectic and hemicellulosic polysaccharides were solubilized. It is concluded that extrusion has promise as a physical process for manipulating both the technological functionality and the health promoting properties of dietary fibers.

Enzymatic deconstruction of backbone structures of the ramified regions in pectins

The pectic enzymes are a diverse group of enzymes that collectively degrade pectin, a mixture of highly heterogeneous and branched polysaccharides rich in D: -galacturonic acids forming a major component of the primary cell wall of plants. This review covers key enzymes that function to deconstruct the "ramified region" of pectin. The enzymes include glycoside hydrolases and polysaccharide lyases that degrade complex pectic domains consisting of rhamnogalacturonans, xylogalacturonans, and other heterogeneous polymers. The chemical nature of the pectic substrates for the enzymes is presented. The biochemical properties of the enzymes, the mechanisms of enzyme actions, and related structures and functions, are described. Applications of these enzymes in fruit juice processing and in the production of bioactive compounds, as well as their technological relevance to the deconstruction of cell wall structures for biomass conversion are discussed.

Conformation and mobility of the arabinan and galactan side-chains of pectin

The function of the arabinan and galactan side-chains of pectin remains unknown. We describe 13C NMR experiments designed to yield spectra from the most mobile polymer components of hydrated cell walls isolated from a range of plant species. In pectin-rich cell walls, these corresponded to the pectic side-chains. The arabinan side-chains were in general more mobile than the galactans, but the long galactan side-chains of potato pectin showed high mobility. Due to motional line-narrowing effects these arabinan and galactan chains gave 13C NMR spectra of higher resolution than has previously been observed from 'solid' biopolymers. These spectra were similar to those reported for the arabinan and galactan polymers in the solution state, implying time-averaged conformations resembling those found in solution. The mobility of the highly esterified galacturonan in citrus cell walls overlapped with the lower end of the mobility range characteristic of the pectic side-chains. The cellulose-rich cell walls of flax phloem fibres gave spectra of low intensity corresponding to mobile type II arabinogalactans. Cell walls from oat coleoptiles appeared to contain no polymers as mobile as the pectic arabinans and galactans in primary cell walls of the other species examined. These properties of the pectic side-chains suggest a role in interacting with water.

Chromatographic study of highly methoxylated lime pectins deesterified by different pectin methyl-esterases

The inter-molecular distribution of free carboxyl groups of two highly methoxylated pectins enzymatically deesterified by plant and fungus pectin methyl-esterases were investigated by size-exclusion (SEC) and ion-exchange chromatography (IEC). "Homogeneous" populations with respect to molar mass or charge density were thereby obtained and their chemical composition and physico-chemical properties (transport parameter for monovalent cations and calcium, calcium activity coefficient) were studied. Chemical analysis showed that the composition varies from one SEC fraction to another, the highest molar mass fraction being richer in rhamnose and galactose and exhibiting a slightly higher degree of methylation. Separation of pectins by IEC revealed a quite homogeneous charge density distribution for F58 contrary to P60 which exhibited a large distribution of methoxyl groups. The free carboxyl groups distributions and calcium binding behaviours of SEC and IEC fractions were shown to differ widely for highly methoxylated pectins deesterified by plant and fungus pectin methyl-esterases.