Insecticidal effects of Ungernia severtzovii bulb extracts against the grain aphid Schizaphis graminum (Rondani)

Insecticidal effect of Ungernia severtzovii bulbs extract has been investigated against the grain aphid Schizaphis graminum. LC₅₀ value of the ethanolic extract of U. severtzovii against the female aphids was 0.235% (2.35 g/l). There was 100% mortality of the subsequent nymphs of the treated females at 0.25-1.0%. The extract was equally active against the nymphs at the highest concentrations. Hexane and ethanolic extracts were the most active against the aphids of all the extracts. Fractionation of the hexane extract by TLC yielded three fractions. Fraction II was the most active (>90% mortality) against the aphids. Xanthoxylin was identified as the major constituent in fraction II of the hexane extract and may be responsible for the insecticidal effect of U. severtzovii.     

Antioxidant, antibacterial, and antiviral effects of Lactuca sativa extracts

Antioxidant, antibacterial and antiviral effects of aqueous and methanol extracts of Lactuca sativa var longifolia leaves were investigated. The antioxidant activity was evaluated using the DPPH assay. The effect of the extracts against 5 Gram-positive and 6 Gram-negative bacteria was tested. The antiviral activity was determined against human cytomegalovirus (HCMV) strain AD-169 (ATCC Ref. VR 538) and coxsackie B virus type 3 (CoxB-3) using a cytopathic effect (CPE) reduction assay. The methanol extract had the highest total phenolic contents (235.31 mg CE/g extract). It exhibited a significantly (p < 0.05) greater hydroxyl radical-scavenging activity (IC₅₀ = 3.5 μg/ml) than the aqueous extract (4.1 μg/ml). It was also the most effective extract with the lowest MIC (2.5 mg/ml) against all Gram negative and Gram positive bacteria. Methanol and aqueous extracts exhibited antiviral activity against HCMV and Cox-B3 viruses with IC₅₀ of 200 μg/ml.     

Mosquitocidal activity of two Bacillus bacterial endotoxins combined with plant oils and conventional insecticides

The full whole culture (FWC), containing parasporal protein toxins of Bacillus thuringiensis israelinsis (Bti) and Bacillus sphaericus 2362 (Bs), either singly or in combination with plant oils and commercial insecticides, was tested against larval and adult stages of Culex pipiens mosquitoes under controlled laboratory conditions. In terms of LC₅₀ values recorded after 24, 48, 72 and 96 h, the bacterial toxins showed high potency towards both larvae and adults of mosquitoes in a dose-dependent manner. Generally, the Bti toxin seemed to be more potent than the Bs toxin. For example, the Bti toxin showed a 24 h LC₅₀ of 8.2 ppm against mosquito larvae compared to 13.6 ppm for the Bs toxin. In the adult bioassay, the obtained 24 h LC₅₀ values were 0.064 and 0.085 mg/cm², respectively for the two bacterial toxins. The bacterial toxins mixed with plant oils or insecticides at equitoxic doses (e.g., LC₂₅ values) mostly showed potentiation effects, either against larvae or adults of the tested insect. Among a total of 14 paired mixtures, only the joint action estimated for the mixture of malathion + Bti or Bs was accounted as additively. Combining Bti or Bs endotoxins at LC₀ with different plant oils and insecticides at LC₅₀ concentration levels each, has resulted in considerable synergism against either larvae or adults. In the case of larval bioassays, the maximum synergistic factor (SF) obtained (ca. 2.0) was entitled to the mixture of Bti + spinosad. In the adult bioassays, the mixtures containing Curcuma longa or Melia azedarach oil extracts with Bti or Bs toxins achieved a SF accounted to 2.0. The results of the present study may be considered as an additional contribution to the area of joint toxicity of biocidal agents combining bacterial toxins, plant oils and traditional insecticides. The reached findings may encourage future research to elucidate its performance under practical field conditions.     

Nemato-toxic potential of Betel (Piper betle L.) (Piperaceae) leaf

In vitro and in-planta trials were conducted to determine the nemato-toxic potential of aqueous leaf extracts of Betel (Piper betle L.) against the root-knot nematode species, Meloidogyne incognita, at five concentrations, standard extract (S) [1:2 (w/v] and its four dilutions, 20%, 40%, 60%. 80% of S. In the in vitro trials, second-stage juveniles (J₂s) and eggs of M. incognita were directly exposed to the extract while in the in-planta trials, the effect of the extract was evaluated as a root dip treatment using tomato plants. The findings indicated that the extract was lethal to J₂s but also inhibited egg hatch. The seedling dip treatments reduced root infestations in terms of gall formation, egg production and J₂ population densities in soil while simultaneously enhancing the growth of tomato plants. All these effects varied in a dose-dependent manner. Based on the LC₅₀ value, the eggs were found to be less sensitive to the extract than J₂s. One hundred percent of mortality of J₂s was recorded at four concentration levels, 40%, 60% and 80% of S and S, while 100% egg inhibition was only recorded at S. The highest reductions in gall formation (i.e., number of galls/root system), egg production and J₂ population were all recorded at S as 83%, 87% and 84% compared to the untreated water control. The maximum growth enhancement, which was 235% of the control, was detected in the root length of treated tomato plants. It appears the aqueous leaf extract of P. betle shows promise as a sustainable eco-friendly nematicide for the management of M. incognita.     

Effects of crude seed extracts of Annona atemoya and Annona squamosa L. against the cabbage looper, Trichoplusia ni in the laboratory and greenhouse

Antifeedant, growth inhibitory and toxic effects of crude seed extracts of Annona squamosa and Annona atemoya from Fazenda Viveiro Bona, Parasisópolis – Minas Gerais, Brazil, were evaluated against the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) using different bioassays. Crude methanolic seed extracts deterred feeding of third instar T. ni larvae in a leaf disc choice bioassay. A. squamosa was ∼10 times more active as a feeding deterrent than A. atemoya (DC₅₀ = 2.3 mg/ml vs. 20.1 mg/ml). A. squamosa was ∼three times more active as a growth inhibitor than A. atemoya (EC₅₀ = 38.0 ppm vs. 117.0 ppm). Methanolic seed extracts of A. squamosa and A. atemoya were toxic to third instar T. ni larvae both through topical and oral application. A. squamosa was more toxic through feeding (LC₅₀ = 167.5 ppm vs. 382.4 ppm) whereas, A. atemoya exerted greater toxicity via topical application (LC₅₀ = 301.3 μg/larva vs. 197.7 μg/larva). Both A. squamosa and A. atemoya extracts reduced leaf area consumption and larval growth in a greenhouse experiment. Our results indicate that both A. squamosa and A. atemoya have potential for development as botanical insecticides, especially for local use in Brazil.     

Rosmarinic Acid from Eelgrass Shows Nematicidal and Antibacterial Activities against Pine Wood Nematode and Its Carrying Bacteria

Pine wilt disease (PWD), a destructive disease for pine trees, is caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus and additional bacteria. In this study, extracts of Zostera marina showed a high nematicidal activity against PWN and some of the bacteria that it carries. Light yellow crystals were obtained from extracts of Z. marina through solvent extraction, followed by chromatography on AB-8 resin and crystallization. The NMR and HPLC analysis showed that the isolated compound was rosmarinic acid (RosA). RosA showed effective nematicidal activity, of which the LC₅₀ (50% lethal concentration) to PWN at 24 h, 48 h and 72 h was 1.18 mg/g, 1.05 mg/g and 0.95 mg/g, respectively. To get a high yield rate of RosA from Z. marina, single factor experiments and an L₉ (3⁴) orthogonal experiment were performed. This extraction process involved 70% ethanol for 3 h at 40 °C. The extraction dosage was 1:50 (w/v). The highest yield of RosA from Zostera was 3.13 mg/g DW (dried weight). The crude extracts of Zostera marina (10 mg/mL) and RosA (1 mg/mL) also showed inhibitory effects to some bacterial strains carried by PWN: Klebsiella sp., Stenotrophomonas maltophilia, Streptomyces sp. and Pantoea agglomerans. The results of these studies provide clues for preparing pesticide to control PWD from Z. marina.     

Cyclodepsipeptides: Isolation from Endophytic Fungi of Sarcophyton ehrenbergi and Verification of Their Larvicidal Activity via In-Vitro and In-Silico Studies

Culex pipiens mosquitoes are vectors to many viruses and can transmit diseases such as filariasis and avian malaria. The present study evaluated the larvicidal activity of marine-derived endophytic fungi Aspergillus nomius and Aspergillus flavus from the soft coral Sarcophyton ehrenbergi along with two known cyclodepsipeptide compounds, scopularide A (1) and B (2), isolated from A. flavus extract, against third-instar larvae of C. pipiens, using distilled water as a negative control and toosenedanin as a positive control. The structures of the isolated compounds were confirmed by various spectroscopic analyses. The lethal concentrations (LC₅₀ and LC₉₀) were calculated by probit analysis. Scopularide A was the most potent after 96 h treatment, with LC₅₀ and LC₉₀ values of 58.96 and 994.31 ppm, respectively, and with 82.66% mortality at a concentration of 300 ppm. To unravel the biochemical mechanism of the tested extracts and compounds, their effects against protease, chitinase, phenoloxidases and lipase enzymes from the whole-body tissue of C. pipiens were evaluated after 72 h treatment at LC₅₀ dose. Superior activity was observed for A. flavus extract against all tested enzymes. A molecular docking study was conducted for scopularide A and B on the four tested enzymes, to further verify the observed activity. Results revealed good binding affinities for both compounds as compared to the docked ligands, mainly via a number of hydrogen bonds. This was the first study to report the isolation of endophytic fungi A. flavus and A. nomius from the marine soft coral S. ehrenbergi. The endophytic fungal extract of A. flavus was found to be a promising source for a natural larvicidal agent against C. pipiens populations.     

Hypocholesterolemic Activity from the Leaf Extracts of Cnidoscolus chayamansa

The aim of this study was to determine the hypocholesterolemic activity of Cnidoscolus chayamansa. In an in vivo model, high-cholesterol diet administered to mice Balb/c induced hypercholesterolemia. Three extracts from Cnidoscolus chayamansa (ethanol, methanol and an aqueous extract) were tested on hypercholesterolemic mice. Active extracts were assessed against the in vitro inhibitory activity of the same three extracts on the HMG-CoA reductase enzyme by using Vero cells. The specific chemical groups present in the phytochemical extracts were also determined. Only the aqueous extract (at either doses employed) showed a significant cholesterol reduction (27.9 and 31.1%, for 50 and 100 mg kg⁻¹, respectively P < 0.01). The extract did not inhibit the HMG-CoA reductase enzyme, suggesting that its compounds act at another level in cholesterol metabolism. Reactions to secondary metabolites indicate the presence of alkaloids in the aqueous and ethanol extracts and phenol hydroxyls in the ethanol and methanol extracts.     

Lethal and sublethal effects of buprofezin and imidacloprid on Bemisia tabaci (Hemiptera: Aleyrodidae)

The sweetpotato whitefly, Bemisia tabaci (Gennadius), has become a major threat to agriculture worldwide. The development of insecticide resistance in B. tabaci has necessitated the exploration of new management tactics. The toxicity of imidacloprid and buprofezin to various life stages of B. tabaci was determined in the laboratory. Also, the sublethal effects of both insecticides were studied on demographic and biological parameters of B. tabaci. Both insecticides were very toxic against first stage larvae of the pest with LC₅₀ values of 1.0 and 19.3 ppm for buprofezin and imidacloprid, respectively. Toxicities decreased between successive stages (LC₅₀ values ranging from 1.0 to 2854.0 ppm). The LC₅₀ values of imidacloprid for adult males, females and eggs were 11.8, 71.6 and 151.0 ppm, respectively. Buprofezin had no significant effect on adults and eggs. The sublethal concentration of imidacloprid had no significant effect on demographic and biological parameters of B. tabaci but the maximal value for the mean generation time (T) (18.8 day) was observed in imidacloprid treatment. Buprofezin significantly decreased stable population and biological parameters of B. tabaci except it did not decrease the rate of population increase or the sex ratio of offspring.     

白藓不同部位水蒸气蒸馏液对玉米蚜生物活性的影响研究

利用均匀设计法研究了白藓根、茎和叶水蒸气蒸馏液对玉米蚜的生物活性。结果表明：白藓根的水蒸气蒸馏液对玉米蚜具有触杀和拒食作用,24h和48h的致死中浓度(LC₅₀)分别为6.48mg/L 和6.77mg/L,48h的致死率达99.8%。白藓叶的水蒸气蒸馏液只有拒食作用,且拒食作用的效果比根更加显著,对玉米蚜24h和48h的拒食中浓度(AFC₅₀)分别为11.45mg/L 和9.88mg/L,其中48h的拒食率达92.5%。白藓茎的水蒸气蒸馏液触杀和拒食作用均不明显。     

Assessment of dermal wound healing and in vitro antioxidant properties of Avena sativa L.

Avena sativa L. (Poaceae) has been reported to have traditional utilization against skin diseases and inflammation. Therefore, in this study, the n-hexane, ethyl acetate, ethanol, and water extracts of A. sativa were investigated for their wound healing and antioxidant activities. Total phenol and flavonoid contents of the extracts were established spectrophotometrically. For the wound healing activity, linear incision and circular excision models on rats and mice were evaluated with a standard ointment Madecassol^®. Antioxidant activity was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, ferrous ion-chelating, and ferric-reducing antioxidant power (FRAP) assays. Significant wound healing activity was observed with the ointment formulation of the ethanol extract at 1% concentration. The histopathological examination results also supported the outcome of both linear incision and circular excision wound models. All of the extracts exerted low antioxidant activity in the applied assays. The present study provides a scientific evidence for the traditional usage of A. sativa in the management of wound healing.     

Efficacy of Plectranthus glandulosus (Lamiaceae) and Callistemon rigidus (Myrtaceae) Leaf Extract Fractions to Callosobruchus maculatus (Coleoptera: Bruchidae)

As part of on-going efforts to use eco-friendly alternatives to chemical pesticides, methanol crude extracts of Plectranthus glandulosus and Callistemon rigidus leaves were sequentially fractionated in hexane, chloroform, ethyl acetate, and methanol to establish the most active fraction(s) against Callosobruchus maculatus in cowpea. Cowpea seeds (25 g) were treated with 0.5, 1, 2, and 4 g/kg of extract to evaluate the contact toxicity and F₁ progeny production of the beetles in the laboratory. Mortality was recorded 1, 3, and 7 d postexposure. P. glandulosus hexane fraction was more toxic than the other fractions recording 100% mortality at 4 g/kg, within 7 d with LC₅₀ of 0.39 g/kg. Hexane fraction of C. rigidus showed superior toxicity, causing 100% mortality at 4 g/kg within only 1 d of exposure with LC₅₀ of 1.02 g/kg. All the fractions greatly reduced progeny emergence, with C. rigidus hexane fraction being the best progeny inhibitor. Fractions of P. glandulosus and C. rigidus leaves had sufficient efficacy to be a component of storage pest management package for C. maculatus.     

Variability in essential oil content and composition of Origanum hirtum L., Origanum onites L., Coridothymus capitatus (L.) and Satureja thymbra L. populations from the Greek island Ikaria

Plants belonging to four “oregano” plant species (Origanum hirtum L., Origanum onites L., Coridothymus capitatus L., and Satureja thymbra L.) were collected during flowering from 33 sites located in the eastern part of the Greek island of Ikaria in the Eastern Aegean during April, May and July 2008. C. capitatus and O. hirtum were mostly observed in higher altitudes, whereas O. onites and S. thymbra in lower ones. The spatial distribution of all species was depicted on a GIS map. All four species exhibited essential oil concentrations higher than those reported in earlier literature, namely O. onites 3-4.3%, S. thymbra 4-6.5%, C. capitatus 3.7-5.6% and O. hirtum 5.5-10.0% (v/w). Carvacrol was the main constituent of the essential oils of all species, followed by γ-terpinene, p-cymene and caryophyllene, while thymol was not detected. All constituents varied remarkably among the four species, with carvacrol exhibiting the lowest variation. Carvacrol content varied between 72.3 and 89.2% in O. onites; 46.5 and 58.0% in S. thymbra; 82.9 and 90.9% in C. capitatus; and 84.4 and 93.8% in O. hirtum. By applying hierarchical cluster analysis on the basis of the essential oil constituents two main groups, divided into four subgroups of the taxa were evident. The first group consisted of O. onites and S. thymbra, while the second one of C. capitatus and O. hirtum. The results are discussed in terms of topography and climatic variation.     

Integrated management of postharvest banana anthracnose (Colletotrichum musae) through plant extracts and hot water treatment

The aim of the present study was to determine the integrated effect of plant extracts and hot water treatment on postharvest anthracnose and banana fruit quality. Artificially inoculated banana fruit were dipped in 10% and 20% (w/v) extracts of four plant species, viz. Acacia albida, Argemone mexicana, Dovalis abyssinica and Prosopis juliflora at room temperature (20 °C), 45 °C and 50 °C. Fruit treated separately with 20% extracts of A. albida and P. juliflora at 50 °C had reduced anthracnose incidence and severity. These treatment combinations also had the highest percentage of marketable ripe banana fruits. In conclusion, applying aqueous plant extracts at 50 °C enhanced the antifungal activity of extracts without affecting the physico-chemical properties of banana.     

Supercritical Fluid Extraction of Fucoxanthin from the Diatom Phaeodactylum tricornutum and Biogas Production through Anaerobic Digestion

Phaeodactylum tricornutum is the marine diatom best known for high-value compounds that are useful in aquaculture and food area. In this study, fucoxanthin was first extracted from the diatom using supercritical fluid extraction (SFE) and then using the extracted diatom-like substrate to produce bioenergy through anaerobic digestion (AD) processes. Factors such as temperature (30 °C and 50 °C), pressure (20, 30, and 40 MPa), and ethanol (co-solvent concentration from 10% to 50% v/v) were optimized for improving the yield, purity, and recovery of fucoxanthin extracted using SFE. The highest yield (24.41% w/w) was obtained at 30 MPa, 30 °C, and 30% ethanol but the highest fucoxanthin purity and recovery (85.03mg/g extract and 66.60% w/w, respectively) were obtained at 30 MPa, 30 °C, and 40%ethanol. Furthermore, ethanol as a factor had the most significant effect on the overall process of SFE. Subsequently, P.tricornutum biomass and SFE-extracted diatom were used as substrates for biogas production through AD. The effect of fucoxanthin was studied on the yield of AD, which resulted in 77.15 ± 3.85 LSTP CH₄/kg volatile solids (VS) and 56.66 ± 1.90 LSTP CH₄/kg VS for the whole diatom and the extracted P.tricornutum, respectively. Therefore, P.tricornutuman can be considered a potential source of fucoxanthin and methane and both productions will contribute to the sustainability of the algae-biorefinery processes.     

Response surface optimization of antioxidants extraction from chestnut (Castanea sativa) bur

The chestnut bur, a forest waste product from chestnut processing in the food industry, was studied as a potential source of natural antioxidants. Extractions were performed using aqueous solutions of methanol or ethanol. Experiments were planned according to an incomplete 3³ factorial design to study the influence of temperature (25-75 °C), time (30-120 min) and solvent concentration (50-90%) on extraction yield and on extract properties: total phenols content, antioxidant activity (using the FRAP, DPPH and ABTS methods) and average molecular weights. All dependent variables were influenced by temperature and solvent concentration whereas the influence of time was almost negligible. Using the response surface methodology the optimal extraction conditions were selected: the highest temperature assayed (75 °C), the lowest solvent concentration (50%) and an extraction time of 75 min for the methanolic extractions and of 30 min for the ethanolic ones. Under those conditions the values predicted for extraction yield and total phenols content were 18.95% and 36.32 g GAE/100 g extract for the methanolic extract and 17.95% and 26.11 g GAE/100 g extract for the ethanolic ones. Methanolic extracts showed superior total phenols content and antioxidant properties and slightly higher extraction yields than ethanolic extracts; however, ethanol is recommended for food applications due to its GRAS (Generally Recognized as Safe) qualification. Gallic acid esters of glucose, ellagic acid and small proportions of quercetin-3-β-d-glucoside, phenolic compounds with demonstrated antioxidant properties, were identified in chestnut bur extracts by RP-HPLC-ESI-TOF.     

Insecticidal activities of crude extracts and phospholipids from Chenopodium ficifolium against melon and cotton aphid, Aphis gossypii

Several organic solvent extracts of Chenopodium ficifolium were tested for their insecticidal activity against melon and cotton aphid, Aphis gossypii, on cucumber plants. Both methanol and ethanol extracts, at 5000 μg ml⁻¹, were highly active giving over 80% control. The other crude extracts displayed moderate or weak insecticidal activity giving control in the range of 16–69%. Two phospholipids were isolated as insecticidal active substances from C. ficifolium. Their chemical structures were identified as 1-palmitoyl-2-(3-trans)-hexadecenoyl-sn-glycero-3-phosphoglycerol and 1-palmitoyl-2-linoleoyl-3-glycerophosphocholine by GC–MS, EDS, mass and NMR spectral analyses. Both compounds displayed a dose-dependent mortality of A. gossypii. Furthermore, the liquid formulation that was obtained by partitioning with n-hexane from the methanol extract of C. ficifolium controlled melon and cotton aphid on cucumber plants effectively. These results indicate that extracts of C. ficifolium have potential for development as botanical insecticides for controlling A. gossypii infesting cucumber plants.     

Efficacy of medicinal plant extracts against Formosan subterranean termite, Coptotermes formosanus

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is among the most devastating termite pests. Natural products derived from plant extracts were tested in a discovery programme for effective, environment friendly termite control agents. Screening for anti-termitic activity of plant extracts with some known medicinal attributes could lead to the discovery of new agents for termite control. The aim of this study was to investigate the anti-termitic activity of crude leaf hexane, ethyl acetate, acetone and methanol extracts of Andrographis lineata Wallich ex Nees. (Acanthaceae), Andrographis paniculata (Burm.f.) Wall. ex Nees. (Acanthaceae), Argemone mexicana L. (Papaveraceae), Aristolochia bracteolata Lam. (Aristolochiaceae), Datura metel L. (Solanaceae), Eclipta prostrata L. (Asteraceae), Sesbania grandiflora (L.) Pers. (Fibaceae) and Tagetes erecta L. (Compositae) against C. formosanus. An impregnated filter paper no-choice bioassay method was followed. All the crude extracts showed anti-termitic activity in a dose-dependent manner and exhibited a significant activity after 24 h and 48 h of exposure; the highest termite mortality was found in leaf hexane extract of A. bracteolata, ethyl acetate extract of A. paniculata, D. metel, E. prostrata, methanol extract of A. lineata and D. metel after 24 h (LD₅₀ = 363, 371, 298, 292, 358 and 317 ppm; LD₉₀ = 1433, 1659, 1308, 1538, 1703 and 1469 ppm), respectively. The hexane extract of T. erecta, acetone extract of A. mexicana, methanol extract of S. grandiflora and T. erecta showed activity after 48 h (LD₅₀ = 245, 253, 289, 409 ppm; LD₉₀ = 1378, 1511, 1508 and 2425 ppm), respectively. Among the natural products tested, may provide a renewable source of safe natural wood preservatives. These findings corroborate traditional insecticidal application of selected plants and the results can be extended for the control of termites. The primary objective of the present study was to identify novel, natural chemotypes from biologically active crude plant extracts that may be useful as part of termite treatment regimens in their natural form or as synthons for structure-activity studies in the future. The results reported here open the possibility of further investigations of efficacy on their anti-termitic properties of natural product extracts.     

Antioxidant activity and phenolic content of chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark extracts

Chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark, waste products of the food and wood industries, respectively, were analysed as potential sources of antioxidant compounds. The extraction yield, the antioxidant activity and total phenols content of the extracts were greater in chestnut shell than in eucalyptus bark for most of the extraction conditions essayed. Extraction of chestnut shell with a 2.5% Na₂SO₃ aqueous solution led to the highest extraction yield, 25.6%, total phenols, 13.4 g gallic acid equivalent/100 g oven-dried shell, and FRAP antioxidant activity, 80.7 mmol ascorbic acid equivalent/100 g oven-dried shell. Extraction with methanol:water (50:50, v/v) provided the best results for eucalyptus bark. The antioxidant activity and the total phenols content of the extracts had a positive linear correlation. FTIR spectroscopy confirmed the higher content of phenolic compounds in chestnut shell extracts compared to eucalyptus bark extracts. Chestnut shell extracts were characterized by the presence of high molecular weight species whereas lower molecular weight species were predominant in eucalyptus bark extracts.     

Water extractable (1→3,1→4)-β-d-glucans from barley and oats: An intervarietal study on their structural features and rheological behaviour

The fine structures and rheological behaviours of aqueous flour dispersions and of β-glucan, (1→3,1→4)-β-d-glucan isolates obtained from 18 registered varieties of normal covered barley seeds and four registered oat varieties, grown in the same location in Greece, were investigated. The β-glucan content of the barleys and oats varied between 2.5–5.4 and 2.1–3.9%, respectively (dry matter basis). Heat treatment of the barley and oat flour dispersions with 80% (v/v) ethanol, to inactivate endogenous β-glucanases, had a stabilizing effect on the viscosity profile of the flour slurries. The relationship between total β-glucan content and aqueous slurry viscosity (at 247 s⁻¹) of the heat-treated barley flours was weak (r²=0.45, p<0.05, n=18). β-Glucans were isolated by water extraction at temperatures slightly below the gelatinization temperature of starch, enzymatic removal of starch and partial removal of contaminating proteins by adjustment to pH 4.0–4.5, and subsequent precipitation of the water-soluble β-glucans with 80% (v/v) ethanol. The cellulosic oligomers released by the action of a (1→3,1→4)-β-d-glucan hydrolase showed cellotriosyl and cellotetraosyl units, accounted for 91.1–92.1% for barley and between 92.4 and 94.1% for the oat preparations; the respective molar ratios of tri- to tetra-saccharides (DP3/DP4) ranged between 2.73–3.05 (barley) and 2.16–2.42 (oat). Steady shear measurements confirmed the random coil type behaviour of freshly prepared β-glucan solutions (5 and 7%, w/v). The rate at which shear thinning began was dependent on both concentration and molecular size of the polysaccharide. Most of the β-glucan dispersions followed the Cox–Merz rule, except Mucio, a variety with high M_w β-glucan (2.39×10⁵). Viscoelastic characterization, at 8% (w/v), of three barley β-glucan aqueous dispersions differing in molecular size, indicated that the low molecular weight sample exhibited shorter gelation time and higher gelation rate (I_E=[dlog G′/dt]_max) than its higher molecular weight counterparts. Small deformation oscillatory measurements on gels of all barley β-glucan isolates (10% (w/v), 7 d storage, 25 °C) revealed a strong negative relationship (r²=0.88, p<0.01) between G′ (1 Hz, strain 0.1%) and apparent M_w of the polysaccharide.