Biodegradation of cell wall components of maize stover colonized by white-rot fungi and resulting impact on in-vitro digestibility

Treatment of crop residues with some species of white-rot fungi can enhance digestibility. This study was conducted to investigate changes in in-vitro dry matter disappearance (IVDMD) and degradation of cell wall constituents in maize (Zea maize L) stover treated with three white-rot fungi: Cyathus stercoreus, Phlebia brevispora and Phanerochaete chrysosporium. Solid fermentation of maize stover for 28 days at 27°C improved IVDMD from 409 g kg^?1 (control) to 514 g kg^?1 for P brevispora and 523 g kg^?1 for C stercoreus. In contrast, growth of P chrysosporium reduced IVDMD from 409 to 298 g kg^?1. All fungi degraded cell wall p-coumaric acid (PCA) and ferulic acid (FA), but P chrysosporium was the least effective in degrading PCA and FA. Conversely, P chrysosporium degraded lignin 1·6 times more effectively than C stercoreus and 1·4 times more than P brevispora, indicating that lignin degradation alone cannot account for the IVDMD enhancement and that degradation of PCA and FA may be important. Hemicelluloses were preferentially and highly utilized by all the fungi. Cellulose was extensively degraded only by P chrysosporium (69% lost after 28 days of incubation), while substrate colonized by the other two fungi retained more than 84% original cellulose. Incubation of C stercoreus and P brevispora decreased the concentrations of both xylose and arabinose, but increased glucose concentration, whereas P chrysosporium removed less xylose and decreased glucose concentration. Preferential removal of arabinose over xylose by the fungi caused an increase in the xylose to arabinose ratio of the treated residues. Enhanced digestibility may have resulted from cleavage of lignin-carbohydrate bonds. Results of this study suggest that digestibility enhancement of maize stover colonized by white-rot fungi is regulated by a complex combination of various factors, including the degradation of structural carbohydrates, cell wall phenolic acids and lignin.     

Four phenolic acids determined by an improved HPLC method with a programmed ultraviolet wavelength detection and their relationships with lignin content in 13 agricultural residue feeds

BACKGROUND: Lignification‐associated phenolic acids are widely distributed in graminaceous plant cell walls. This study developed a rapid and sensitive reversed‐phase method for the simultaneous quantification of protocatechuic (PRA), vanillic (VA), ferulic (FA) and p‐coumaric (PCA) acids and investigated the relationship between these compounds and lignin contents in 13 fibrous feeds. RESULTS: The phenolic acids were identified at a column temperature of 15 °C in a single run, in which the wavelength was programmed at 260 nm for PRA and VA, then switched to 310 nm for FA and PCA determinations. Satisfactory precision, recovery, and linearity were obtained with this method. Among 13 feeds, PCA was most abundant, followed by FA, VA and PRA. Great variations in phenolic acid and lignin contents were found. FA content was much richer than PCA content in maize and wheat brans, and the highest PCA content occurred in maize stalks. Lignin content was correlated with proportions of FA (r = ? 0.95) and PCA (r = 0.90) in the summed phenolic acids and the PCA:FA ratio (r = 0.91). CONCLUSION: The improved method appears to be useful for simultaneous quantification of target phenolic compounds. Both FA and PCA may be good indicators for plant cell wall lignification associated with feed digestibility. Copyright © 2012 Society of Chemical Industry     

Relationship between Phenolic Acids Formed During Rumen Degradation of Maize Samples andin vitroDigestibility

The organic matter (OMD) and cell wall (CWD) digestibility of stalks of 25 different maize samples were determined in an in vitro assay using rumen fluid. The stalk OMD and CWD varied between 62–80% and 44–62%, respectively. The free phenolic acids formed in the liquid phase during fermentation in in vitro incubations were assessed by HPLC and ¹H NMR. The following nine phenolic acids could be demonstrated to be present: p -hydroxybenzoic (HBA), p -hydroxyphenylacetic (HPAA), vanillic (VA), syringic (SYRA), 3-(4-hydroxyphenyl)propionic (HPPA), p -coumaric (PCA), ferulic (FA), phenylacetic (PAA) and 3-phenylpropionic (PPA) acids. Large variation was observed among the maize samples for all phenolic acids identified. The most abundant phenolic acids, PPA, PAA and HPAA were present in concentrations ranging from 0·57 to 1·41 mM, 0·32 to 0·46 mM, and 71 to 105 μM, respectively, and were present as free monomeric molecules. HBA concentrations ranged from 6·9 to 21·1 μM and this acid was also present as free molecules. The other phenolic acids could only be observed after NaOH treatment of the liquid phase and were detected in minor amounts (0 to 12 μM). Correlation studies revealed a negative relation between digestibility and NaOH labile esters in the medium (ie PCA, FA, VA and SYRA esters) and a positive relationship between digestibility and PPA and PAA. When path analysis was applied, an inverse effect of PCA esters in the medium on both OMD and CWD ( r =-0·71 and −0·56, respectively) was observed and a high positive effect of PPA acid on CWD ( r =+0·67). Principal component analysis revealed close associations between released phenolic acid esters, neutral detergent fibre, and cell wall esters of PCA and FA.     

Cell wall composition and degradability of forage stems following chemical and biological delignification

Chemical and biological delignification methods were used to investigate the relationship between the concentration and composition of lignin and degradation of forage cell walls. Stem material from lucerne (Medicago sativa L), smooth bromegrass (Bromus inermis Leyss) and maize (Zea mays L) stalks was treated with alkaline hydrogen peroxide, potassium permanganate, sodium chlorite, sodium hydroxide, nitrobenzene, and the lignolytic fungus Phanerochaete chrysosporium. Klason lignin and esterified and etherified phenolic acids were delermined. Cell wall neutral sugar and uronic acid composition and the extent of in-vitro degradability were measured. Chemical delignification generally removed lignin. but the fungal treatment resulted in the removal of more polysaccharide than lignin. The concentrations of esterfied and etherified p-coumaric and ferulic acids were generally reduced in treated cell walls; chlorite treatment preferentially removing p-coumaric acid whereas nitrobenzene treatment removed more ferulic acid. Syringyl moieties were completely removed from the core lignin polymer by nitrobenzene treatment of forage stems. Alkaline hydrogen peroxide and nitrobenzene were generally the most effective delignification treatments for improving polysaccharide degradability, with the grass species responding similarly to delignification whereas lucerne was somewhat less responsive. Fungal delignification, under these experimental conditions, did not improve cell wall degradability of these forages. Multiple regression and covariate analyses indicated that the lignin components measured were not powerful predictors of cell wall degradability. Neither the concentration nor the composition of the lignin fractions was consistently correlated with degradation. This lack of effect was attributed to the more generalised disruption of the cell wall matrix structure by delignification treatments.     

Fungal pretreatment of wheat straw: Effects on the biodegradability of cell walls,structural polysaccharides,lignin and phenolic acids by rumen microorganisms

Disappearance of cell wall components of untreated straw and straw treated with the ligninolytic white-rot fungi Phanerochaete chrysosporium, Dichomitus squalens and Cyathus stercoreus were determined during the course of rumen digestion of samples in nylon bags. The first fungus degraded hemicelluloses and cellulose non-selectively, adversely affecting the digestion rate of crude cell walls. Dichomitus squalens and C. stercoreus preferentially degraded hemicelluloses and lignin, affording cell wall degradation rates 1.5 times higher than in native straw. Furthermore, the extent of cell wall digestion was also significantly enhanced. Both strains improved the extent of cellulose digestion, whereas the potentially degradable xylan fraction remained unchanged. Polysaccharide digestion rates were influenced in different ways depending on the strain tested: straw degraded by C. stercoreus showed an increase in cellulose digestion rate by 50%, whereas residual arabinose units were slowly degraded. Xylan was degraded 1.8 times faster in straw decayed' by D. squalens, while cellulose digestion remained unchanged. Phanerochaete chrysosporium depressed both xylan and cellulose digestion rates. Fungal-treated lignins were solubilised in the rumen faster than in untreated straw, whereas only treatment by C. stercoreus resulted in higher lignin losses. Esterified phenolic acids were extensively degraded by all three fungi. Residual ferulic and p-coumaric acids accumulated during rumen digestion, although only the former decreased in the original straw.     

Chemical composition and biodegradability of crop residues colonized by white-rot fungi

Two experiments were conducted to study the degradation of rice (Oriza sativa L) straw and maize (Zea maize L) stover by selected white-rot fungi, using loss of organic matter, disappearance of cell wall constituents, and in-vitro dry matter digestibility (IVDMD) as indices of rumen microbial degradation. Four white-rot fungi—Cyrathus stercoreus, Dichomitus squalens and two strains (cellulase-less mutant and a wild type) of Phanerochaete chrysosporium—were selected for the first experiment. After 30 days of solid state fermentation. C stercoreus increased IVDMD of both substrates from 373 g kg^?1 (rice) and 393 g kg^?1 (corn) to approximately 540 g kg^?1 by selectively degrading hemicellulose as opposed to cellulose. The highest IVDMD was obtained with a minimal loss of dry matter (33 g kg^?1). In contrast, both strains (wild and mutant) of P chrysosporium degraded cellulose and hemicellulose indiscriminately, and thus lowered the IVDMD to 276. 257 as opposed to 373 for rice straw and 301. 307 as opposed to 393 g kg^?1 for maize stover. All the fungi showed a preference for degrading maize stover compared with rice straw, although the materials were similar in cellulose and lignin concentration. No direct correlation was found between lignin degradation and the improvement of substrate IVDMD of either substrate. The objective of the second experiment was to determine the rate and extent of digestibility of rice straw colonized by C stercoreus during two incubation periods (15 and 30 days). Dry matter disappearance (DMD) was determined by ruminal incubation of the substrate contained in nylon bags. The 30-day incubation period was superior (1.3 ×) to that of the 15-day period in improving in-situ DMD. Treatment of rice straw for 30 days not only improved the extent of dry matter digestibility (616 as opposed to 389 g kg^?1), but also increased (1.5 ×) the rate of disappearance of substrate.     

Relationship of cell wall composition to in vitro cell wall digestibility of maize inbred line stems

The phenolic equipment of maize stem tissues was investigated in relation to the feeding value of the detergent fibre components. Sixteen maize inbred lines, including three brown‐midrib 3 mutants and their normal counterparts, were selected for highly divergent in vitro cell wall digestibility. These lines were grown during two years. Maize stems were analysed for detergent fibre concentration, esterified and etherified p‐hydroxycinnamic acids, lignin content and structure and in vitro digestibility. A large genotypic variation was found for neutral detergent fibre, cell wall phenolic composition and cell wall digestibility. Within the normal maize lines the in vitro neutral detergent fibre digestibility (IVNDFD) of stem fractions was negatively correlated with their Klason lignin content. A multiple regression model based on esterified p‐coumaric acid and lignin composition as two explanatory variates accounted for 58% of the IVNDFD variation. In this study, three normal maize inbred lines displaying a lignin content and a cell wall digestibility level close to those observed in the three bm3 lines could be detected, which opens up new breeding avenues. © 2000 Society of Chemical Industry     

Changes in fatty acid content and composition in silage maize during grain filling

BACKGROUND: The stage of maturity at harvest has a major effect on the fatty acid (FA) content and composition of forage plants consumed by dairy cows. The present study investigated the dynamics of FA content and composition in stover (leaves and stem) and ears (cob, shank and husks) of two maize genotypes (G2 and G6) grown on sandy and clay soils and harvested at 14, 42, 56, 70 and 84 days after flowering (DAF). In addition, the FA content and composition of six maize genotypes (G1‐G6) grown on the two soil types were compared at the normal harvest time of early genotypes in the Netherlands (70 DAF). RESULTS: The contents of total FAs and major individual FAs in both stover and ears changed significantly (P < 0.001) during the grain‐filling period (14‐84 DAF). In stover the contents of C16:0, C18:2, C18:3 and total FAs declined (P < 0.001) while those of C18:0 and C18:1 increased (P < 0.001) with progressive grain filling. The rate of decline in C18:3 and total FA contents was slower during 14‐56 DAF as compared with 56‐84 DAF. In ears, the contents of C16:0, C18:1, C18:2 and total FAs increased up to 56 DAF and then remained more or less constant until 84 DAF. At 70 DAF the content of polyunsaturated fatty acids (PUFAs) in both stover and ears did not differ among the six genotypes. However, the average contents of C16:0, C18:3 and total FAs in stover were higher (P < 0.05) on clay soil, whereas those of C18:0 and C18:1 were higher on sandy soil. CONCLUSION: The results demonstrate that the maximum PUFA content in silage maize is harvested around 56 DAF, in the present study at a T_sum of 927 °C.d or at an ear dry matter content of 440 g kg^?1, which is before the onset of rapid senescence. Any further delay in harvesting will cause a rapid decline in C18:3 content in maize silages. Copyright © 2011 Society of Chemical Industry     

p-Coumaric and ferulic acid components of cell walls of ryegrass and their relationships with lignin and digestibility

Cell walls, isolated from vegetative Italian ryegrass, pre- and post-flowering perennial ryegrass and the faeces of sheep fed the perennial ryegrass, were treated with alkali and the liberated p-coumaric acid (PCA), ferulic acid (FA) and vanillin estimated. A higher yield of the two acids was obtained from the Italian than from the perennial ryegrass. Oxidation of the cell-wall residues indicated the presence of the 1-phenylpropene structural unit in the lignin cores. There was a highly significant correlation between the digestibility of the cell walls from perennial ryegrass and the FA/PCA ratio. The recovery of PCA (24 to 59 %) from the faecal cell walls was much higher than that of FA (5 to 21 %). For each acid this recovery was lower in the pre-flowering herbage.     

Light microscopic analysis of Tectona grandis L.f. wood inoculated with Irpex lacteus and Phanerochaete chrysosporium

Felling of immature teak (Tectona grandis L.f.) trees or delay in transport of wood logs from felling sites provide platform to microbial attack. Among them, white rot fungi are central driving force that degrades wood and causes severe economic loss. In contrast, Phanerochaete chrysosporium and Irpex lacteus are more extensively studied for their ability to degrade synthetic dyes and poly-aromatic compounds. Therefore, in the present study, both the fungi collected from the Gujarat forest were utilised for in vitro decay test to assess their potential in lignin degradation, extent of cell wall damage and pattern of wood decay in sound blocks of teak. In the early stage of fungal inoculation, there was a negligible amount of weight loss; after 1 month it became rapid and highest weight loss (30.05 % by P. chrysosporium and 27.97 % by I. lacteus) was observed at the end of 120 days. Mycelial invasion occurred through vessels, from vessels to axial and ray parenchyma and subsequently into xylem fibres. Both the strains showed selective delignification and the first symptom of degradation was defibration, separation of rays, and formation of boreholes on ray cell walls at an advanced stage. Xylem fibres and parenchyma cells lost their integrity and collapsed completely. Among all the cell types, parenchyma cells and fibres were more vulnerable to fungal attack, while vessels were resistant to the activity of lignolytic enzymes.     

Effect of two pre-treatments on phenolic acid yield in three forage species

A direct comparison of two pre-treatments was undertaken to test their effect on the recovery of phenolic acids (PA) from three forage species. Samples of lucerne (Medicago sativa L), reed canarygrass (Phalaris arundinacea L), and switchgrass (Panicum virgatum L) were refluxed with 95% ethanol (EtOH) or neutral detergent solution (NDS). Subsequently, the resulting ethanol insoluble residue (EIR) and neutral detergent fibre (NDF) were treated with 1 M NaOH, and the extract was assayed for concentrations of p-coumaric acid (PCA) and ferulic acid (FA). In lucerne, the concentration of PCA was 9 times greater in the EIR than in the NDF (0·90 vs 0·11 mg g^?1 dry matter, DM), and the FA concentration was 27 times greater in forage treated with EtOH than with NDS (1·89 vs 0·07 mg g^?1 DM). In reed canarygrass (RCG), the concentrations of PCA and FA were slightly though significantly higher when the forage was pre-treated with EtOH. No significant differences in PA yield were detected between pre-treatments in switchgrass (SG). Extraction of EIR with hot EDTA (0·025 M , pH = 6·8) removed 80 to 90% of the total PA in EIR in lucerne but less than 5% of the PCA and FA in the grasses. These results indicate that almost all the PA in lucerne, in direct contrast to the grasses, are present in a fraction of the plant that is soluble in NDS. The relatively high PA concentration in the NDS soluble fraction suggests that the structure and composition of the fraction to which PA is esterified influence the degree to which PA affects digestibility.     

Immunocytochemical localisation of para-coumaric acid and feruloyl-arabinose in the cell walls of maize stem

Two phenolic compounds, p-coumaric acid and feruloyl-arabinose, were localised by immunocytochemistry in the cell walls of the apical internode of two lines of maize (Co125 and W401) of different digestibility. The compounds were detected at two stages of cell maturity in the lignified tissues (sclerenchyma, fibres and xylem) and in the medullary parenchyma, which, in the samples studied, was not lignified. p-Coumaric acid is a phenolic acid associated with lignins, which confer resistance on plant cell walls to microbial degradation in the rumen. Feruloyl-arabinose is a compound associated with xylans, the principal hemicelluloses in Gramineae, which are potentially degradable. Labelling of p-coumaric acid decreased in both maize lines with cell age and as the cell walls became lignified. The mass of lignin deposited in the cell walls masked p-coumaric acid, thereby making it less accessible to the antibodies. There was an inverse relationship in the labelling of p-coumaric acid and feruloyl-arabinose. Feruloyl-arabinose was more heavily labelled as the plant cell walls matured in all the lignified tissues of both maize lines and in the parenchyma of the less digestible line. All tissues except the parenchyma were more heavily labelled with both sera in Co125, the more digestible line. © 1998 Society of Chemical Industry.     

Antifungal effect of organic acids from lactic acid bacteria on Penicillium nordicum

The control of fungal contamination is particularly important to avoid both spoilage of food and feed products and the occurrence of toxic compounds, known as mycotoxins. Some lactic acid bacteria (LAB) strains have shown the capacity to inhibit fungal growth and the production of mycotoxins. In this work, cell-free supernatants (CFS) of Lactobacillus plantarum UM55 and Lactobacillus buchneri UTAD104 were tested against Penicillium nordicum radial growth and OTA production. When CFS of these strains were used, the radial growth of the fungus was inhibited by less than 20%, but the production of OTA was reduced by approx. 60%. These antifungal effects resulted from organic acids produced by LAB. The CFS of L. plantarum UM55 contained lactic acid, phenyllactic acid (PLA), hydroxyphenyllactic acid (OH-PLA) and indole lactic acid (ILA), while L. buchneri UTAD104 CFS contained acetic acid, lactic acid and PLA. These organic acids were further tested individually for their inhibitory capacity. Calculation of the inhibitory concentrations (ICs) showed that acetic acid, ILA and PLA were the most effective in inhibiting P. nordicum growth and OTA production. When the inhibitory activity of LAB cells incorporated into the culture medium was tested, L. buchneri UTAD104 inhibited the production of OTA entirely in all conditions tested, but fungal growth was only inhibited completely by the highest concentrations of cells. Acetic acid production was primarily responsible for this effect. In conclusion, the ability of LAB to inhibit mycotoxigenic fungi depends on strain capability to produce specific organic acids, and those acids may differ from strain to strain. Also, the use of LAB cells, especially from L. buchneri, in food products prone to contamination with P. nordicum (e.g. dry-cured meats and cheeses) may be an alternative solution to control fungal growth and OTA production.     

The effect of feeding pods of multipurpose trees (MPTs) on the degradability of dry matter and cell wall constituents of maize stover and alfalfa incubated in the rumen of sheep

This study evaluated the effects of feeding alfalfa and pods of tree legumes on rumen pH and ammonia concentration as well as in sacco degradability of dry matter and fibre constituents of maize stover, alfalfa hay and their neutral detergent extracts. The feeds were incubated in the rumens of five South African Merino sheep fed individually in an incomplete (5 × 4) Latin square design using five diets. The diets comprised equal proportions of pasture hay and either alfalfa (Alfalfa diet) or pods of Acacia sieberiana (Sieberiana diet), Acacia nilotica (Nilotica diet) or Leucaena leucocephala (Leucaena diet). The fifth diet was composed of pasture hay alone (Hay diet) and served as a negative control. Supplementation of hay with either legume pods or alfalfa significantly (p < 0.05) increased rumen ammonia concentration from 56 to a maximum of 86 mg l^?1. The pH of the rumen fluid ranged between 6.2 and 6.5 for all diets, but variations in pH were not significant. Diet did not affect (p > 0.05) the degradability constants lag time (LT), slowly degradable fraction (B), potential degradability (PD), effective degradability (ED) and rate of degradation (C) of dry matter (DM) but significantly (p < 0.01) affected ED of the fibre constituents of the incubated feeds. The effective degradabilities of the incubated feeds differed (p < 0.001), with alfalfa and maize stover having average values of 555 and 318 g kg^?1 DM respectively. The rate of degradation of alfalfa was also higher (p < 0.01) than that of maize stover. Neutral detergent extraction improved ED of the cell wall constituents of maize stover but produced the opposite effect for alfalfa. The interactions between incubation feed and extract were significant (p < 0.01) for ED and C of neutral detergent fibre and hemicellulose. The observations show that pods from tree legumes are comparable to alfalfa in the provision of rumen ammonia but limit microbial activity in the degradability of fibre constituents. They also show that maize stover and alfalfa differ in their degradabilities and that the differences may be attributed to their cell wall chemistry. © 2001 Society of Chemical Industry     

Impact of methyl 5-O-(E)-feruloyl-α-L-arabinofuranoside on in-vitro degradation of cellulose and xylan

Abstract : The potential for inhibition of ruminal cell wall degradation by soluble phenolic acid-carbohydrate complexes was assessed using a synthetic molecule, methyl 5-O-(E)-feruloyl-α-L -arabinofuranoside (FA-Ara). In-vitro 24 and 72 h degradabilities of glucose from microcrystalline cellulose, and neutral sugars and uronic acids of oat spelts xylan were determined. Treatments included 0 (Control), 15, 150, 1500, and 4500 μmol liter^?1 of methyl α-L -arabinofuranoside (Me-Ara), FA-Ara, or ferulic acid (FA). Additions of 1500 and 4500 μmol liter^?1 Me-Ara; 15 and 150 μmol liter^?1 FA-Ara; as well as 4500 μmol liter^?1 FA significantly (P < 0·05) decreased 24 h cellulose degradation. Arabinose degradation from xylan after 24 h was decreased (P < 0·05) by 1500 and 4500 μmol liter^?1 concentrations of Me-Ara and FA-Ara. No inhibitory effects of added compounds on 72 h glucose, xylose, or arabinose degradability were observed. Very little FA-Ara remained intact after 24 h. Following 72 h, no added FA-Ara was detectable, suggesting extensive degradation by microbial feruloyl esterases. Extent of polysaccharide degradation, in vitro, was not limited by a soluble phenolic acid-carbohydrate compound, which accurately models a known cell wall complex.     

Molecular Identification of Spoilage Fungi Isolated from Fruit and Vegetables and Their Control with Chitosan

This study investigated fungal spoilage of fruits and vegetables in Saudi Arabia. Activities of cell wall degrading enzymes in fungal isolates were measured. We evaluated the fungicidal activities of chitosan against spoilage fungi. Thirty-three fungal species belonged to 21 fungal genera were collected during this study. ITS sequencing results showed that Alternaria tenuissima, Fusarium chlamydosporum, Penicillium sumatrens, Rhizopus stolonifera, and Trichoderma harzianum were the most common species. The diversity of cell wall degrading enzyme produced by the spoilage fungi revealed that xylanase was the most widely distributed enzyme in fungi followed by amylase and cellulase. Some strains of Macrophomina phaseolina, Trichoderma harzianum, Trichoderma asperellum, Aspergillus niger and Alternaria consortialis showed the highest enzymes activities among tested fungi. Four different concentrations of chitosan (20, 30, 50, and 100 mg/L) were investigated against 22 fungal species. All investigated concentrations of chitosan showed highly significant reduction in the average of radial growth of all tested fungi.     

Integrated management of insect vectors of Aspergillus flavus in stored maize, using synthetic antioxidants and natural phytochemicals

The purpose of this study was to investigate the insecticidal activity of two benzoic acids 2(3)-tert-butyl-4 hydroxyanisole (BHA) and 2,6-di(tert-butyl)-p-cresol (BHT); two phenolic acids 3-phenyl-2-propenoic acid (CA) and trans-4-hydroxy-3-methoxycinnamic acid (FA) and two essential oils of Eugenia caryophyllata (clove tree) and Thymus vulgaris (thyme) against Sitophilus zeamais, Tribolium confusum and Rhyzopertha dominica, vector carriers of aflatoxigenic fungi in stored maize. The susceptibility of insects, the frequency of isolation of Aspergillus section Flavi in insects and maize, and the analysis of aflatoxin B₁ in maize were determined. BHA, BHT, BHA/BHT mixture and the natural phytochemicals AF and AF/AC mixture showed the highest insecticidal activity against S. zeamais, T. confusum and R. dominica after 120 days of incubation. The insecticidal efficacy of the volatile fraction of essential oils of clove and thyme showed less inhibition. There was no contamination of Aspergillus section Flavi in dead and live insects collected from maize treated with BHA. No aflatoxin B₁ accumulation was detected in the control and treatments. The information obtained shows that these substances have the potential to control pest insect vectors of aflatoxigenic fungi in stored maize in microcosms during 120 days.     

The phenolic acid and polysaccharide composition of cell walls of bran layers of mature wheat (Triticum aestivum L. cv. Avalon) grains

The purpose of this study was to examine the carbohydrate and phenolic‐ester composition of cell walls in wheat bran layers. Four defined layers of wheat bran were separated manually from mature grains of wheat (Triticum aestivum L. cv. Avalon) to give samples of beeswing bran (outer pericarp), cross cells, testa + nucellar epidermis and aleurone cells. The cell‐wall material from each layer, and from a sample of intact bran, was analysed for carbohydrates and wall‐bound esterified phenolic acids. The cell‐wall material of intact bran was rich in arabinose and xylose with significant quantities of glucose and uronic acid and a relatively small amount of galactose and mannose. The varying ratios of arabinose:xylose in cell walls of isolated bran layers indicated that the heteroxylans had tissue‐specific substitution patterns. HPLC analysis of phenolic acids identified significant amounts of esterified ferulic acid and 8‐8′‐ (aryltetralin form), 5‐8′‐, 5‐5′‐, 8‐0‐4′‐ and 5‐8′‐(benzofuran form)‐dehydrodiferulic acids in the isolated cell walls. Ferulic acid was highly concentrated in the aleurone layer, whereas dehydrodiferulates were concentrated in the beeswing bran and cross cells. The role of phenolic cross‐linking is discussed in relation to the architecture of the cell walls of wheat bran and to processing implications. Copyright © 2005 Society of Chemical Industry     

Phenolic constituents of mesophyll and non-mesophyll cell walls from leaf laminae of Lolium perenne

trans-Ferulic acid was the main phenolic constituent released when walls of mesophyll and non-mesophyll cells from leaf laminae of Lolium perenne L. were treated with sodium hydroxide. cis-Ferulic, trans and cis-p-coumaric, p-hydroxybenzoic and diferulic acids were also present. Mesophyll and non-mesophyll cell walls contained similar amounts of ferulic acid (approximately 6 mg g^?1 cell wall), but mesophyll walls contained only small amounts of p-coumaric acid (0.4 mg g^?1 cell wall) compared with those of non-mesophyll (3 mg g^?1 cell wall).     

Determination of phenolic acids in plant cell walls by microwave digestion

Microwave digestion (750 W for 90 s) with 4 M NaOH was used to release esterified and etherified hydroxycinnamic acids from cell walls of maize (Zea mays L), wheat (Triticum aestivum L), barley (Hordeum vulgare L) and oilseed rape (Brassica napus L) stems. Subtraction of values for saponifiable phenolic acids obtained after treatment with I M NaOH at room temperature from digest results provided a measure of β-ether linked units. These were exclusively (E + Z)-ferulic acid in the cereal straws. Only trace amounts of ether- and ester-linked hydroxycinnamic acids were released from the dicotyledon, ripe straw. Microwave digestion was shown to be an order of magnitude more effective than dioxane-HCl at liberating β-ether bound phenolic acids and as effective, but substantially quicker, than previously described high-temperature alkaline digestions.