FERULIC ACID IN BARLEY CELL WALLS: A FLUORESCENCE STUDY

Cell walls isolated from barley endosperm have been examined using ultraviolet fluorescence microscopy in parallel with microspectrofluorimetry. The endosperm cell wall fragments exhibit a pale blue autofluorescence. The fluorescence emission spectrum of the walls closely corresponds to the spectrum of ferulic acid, having an emission maximum at a wavelength of 445 nm under the conditions used (excitation maximum at 365 nm). The results provide further evidence that ferulic acid-carbohydrate complexes are localized in barley endosperm cell walls. Similar complexes may be present in aleurone cell walls in relatively high concentrations.     

Monomeric and dimeric phenolic constituents of plant cell walls—possible factors influencing wall biodegradability

A range of plant cell walls fiom graminaceous and leguminous plants were examined qualitatively and quantitatively for monomeric and dimeric phenolic constituents that were released by treatment with sodium hydroxide. The total amounts of phenolics released fiom the walls of the graminaceous plants varied fiom 8 to 28 mg g^?1 walls compared with less than 3 mg g^?1 walls jiom the legumes. p-Coumaric and ferulic acids were the major components of the monomeric fraction. The cell walls also contained substituted cyclobutanes having molecular weights equal to two p-coumaric acid molecules, two ferulic acid molecules or one p-coumaric plus one ferulic acid molecule, All the walls contained dehydrodiferulic acid. If it is assumed that the substituted cyclobutanes and dehydrodiferulic acid arise from dimerisation of feruloyl and p-coumaroyl groups linked to cell wall polysaccharides, then, for the graminaceous walls, it is calculated that between 5 and 14% of these groups had converted to dimers. This dimerisation process may limit the biodegradability of the wall polysaccharides.     

Production and characterisation of two wheat-bran fractions: an aleurone-rich and a pericarp-rich fraction

Wheat bran is a good source of dietary fibre in the form of cell walls, but contains a number of different cell types. We describe a large-scale procedure for the production of an aleurone-rich and a pericarp-rich fraction from hard, Australian wheat. The fractions were characterised by field-emission scanning electron microscopy, by using a range of bright-field stains, colour reagents, and fluorochromes, and by chemical analysis of the walls. The aleurone fraction included the seed coat with its cuticle. Only the pericarp walls showed a histochemical reaction for lignin. The concentrations of ester-linked ferulic acid and (1-->3),(1-->4)-beta-glucans were greater in the aleurone-rich fraction than in the pericarp-rich fraction. The results are consistent with the arabinoxylans in the walls of the pericarp-rich fraction being more highly substituted with arabinose than those in the walls of the aleurone-rich fraction. When the fractions were fed as a dietary supplement to rats and walls were isolated from the faeces, it was found that the pericarp walls were not degraded, but the aleurone walls were partially degraded.     

Charakterisierung mechanisch modifizierter Stärke

Characterization of Mechanically Modified Starch. It is shown that the mechanical strain of starch in form of a plastic starch granule deformation changes its physical and chemical properties in optimal way. The amount of energy required for deformation is although small but it can not be transferred efficiently with tools known at present. Inspite of high losses of energy, the association and polymerisation of starch molecules will be changed extensively due to short time of treatment. Mainly the secondary valence bonds will be dissolved. At the same time occurs a break up of principal valence bonds of both starch components, whereby amylopectin is affected more than amylose. The reduction of hydrogen bonds between neighbouring starch polymers and the resulting increase of free hydroxyl groups and the decomposition of polymers due to breaking up of principal valence bonds lead to changed behaviour of starch towards water. As far as the application is concerned, it was especially emphasised that homogeneous and stable pastes can be prepared with mechanically modified starch, with do not show gel formation and have a high freeze-thaw-stability. More over, the susceptibility to enzymes is improved and the formation of adsorption and inclusion complexes is supported.     

Laccase-aided protein modification: Effects on the structural properties of acidified sodium caseinate gels

Trametes hirsuta laccase (EC 1.10.32) alone was not able to cross-link proteins effectively unless high dosages were used. Incorporation of ferulic acid enhanced the formation of intermolecular cross-links. Cross-linking was more effective when the reaction was carried out at 45 °C rather than at room temperature. Size exclusion chromatography showed that ferulic acid monomers disappeared from the solution in the presence of laccase. Force at rupture point of the caseinate gels treated with laccase without ferulic acid was not significantly different from the control, while stronger gels were achieved when ferulic acid was present. Rheological measurements showed that laccase treatment together with ferulic acid resulted in higher G′ values than the control. Gels were analyzed with confocal laser scanning microscope. A finer network was observed when the enzyme was used together with ferulic acid. Slight proteolytic activity resulted in a negative effect on the gel firmness and microstructure when laccase was used without ferulic acid.     

Interaction Between Ovomucoid and Lysozyme

The interaction between ovomucoid and lysozyme was investigated by precipitation experiments, polyacrylamide gel electrophoresis and inactivation experiments on ovomucoid. The ovomucoid-lysozyme mixture produced turbidity at low salt concentrations over the pH range 6–11. Although both ovomucoid and lysozyme solutions (0.2%, pH 8.5) yielded no precipitation when heated separately at 80°C for 10 mm, about 40% of the proteins in the 0.2% solution of the ovomucoid-lysozyme mixture (2:3, in weight; 1:3, in mole) was precipitated by the same treatment. Ovomucoid was found to form complexes with lysozyme, some of which were precipitated by centrifugation (2000 ×g, 20 mm), and it was presumed that ovomucoid and lysozyme molecules were brought close together by the electrostatic attractive force, unfolded by heating, and then aggregated through intermolecular forces such as hydrophobic forces, hydrogen bonds and disulfide bonds.     

淀粉样纤维-阿魏酸水凝胶的制备及其性质

为提高阿魏酸的负载率和稳定性，将蛋白质在酸性条件下热处理形成淀粉样纤维作为载体，与阿魏酸自组装形成水凝胶，考察不同淀粉样纤维质量浓度、阿魏酸添加量及pH值对阿魏酸负载率的影响，优化水凝胶制备条件。利用红外光谱、内源荧光光谱、X射线衍射、扫描电镜、流变仪等探究蛋白质结构变化、水凝胶的微观结构、凝胶特性等，考察多酚添加量对水凝胶结构和性质的影响。利用超高效液相色谱测试不同环境中水凝胶中阿魏酸的光热稳定性，采用体外模拟消化系统考察阿魏酸的缓释能力。结果表明，当淀粉样纤维质量浓度70 g/L、阿魏酸添加量0.6%、pH 5条件下水凝胶体系中阿魏酸负载率最佳达6.99%，且水凝胶可有效减少阿魏酸在光热环境下的降解速率，提升其光热稳定性。蛋白纤维化形成淀粉样纤维其二级结构α-螺旋和β-折叠占比显著升高，三级结构形成聚集前体状态，更利于结合多酚形成结构稳定的水凝胶。当阿魏酸添加量为0.6%时，阿魏酸-淀粉样纤维水凝胶凝胶性最佳、分子间结构最紧密、储能模量最高（1 655.5 Pa）、溶胀度最低（160%），此时样品在体外模拟消化系统表现出最佳的缓释性能。     

An explanation for the combined effect of xylanase–glucose oxidase in dough systems

In the bakery industry, glucose oxidase is usually used in combination with xylanase. Although many theories exist on the mechanism of action of each enzyme, the positive effect of combining the two is as yet unexplained. In this paper we studied a possible basis for this synergy by focusing on the involvement of arabinoxylans. Water‐extractable arabinoxylans and water‐unextractable solids were studied in dough with or without glucose oxidase. Addition of glucose oxidase led to a stiffer and less extensible dough. Addition of arabinoxylans caused a further decrease in dough extensibility. Addition of xylanase could correct for this decrease. The role of arabinoxylans was further investigated by studying modified water‐extractable arabinoxylans and the effect of agents affecting arabinoxylan crosslinking (ferulic acid). Water‐extractable arabinoxylan was modified with xylanase to generate a low‐molecular‐weight fraction (WEAX_XYL). Alternatively, it was modified with NaOH to prepare a fraction with a decreased ferulic acid content (WEAX_OH). Addition of modified arabinoxylans diminished the effect of glucose oxidase. Glutenin macropolymer and water‐extractable arabinoxylan viscosity experiments were performed to obtain further detail on the role of arabinoxylans (AX). These results give rise to a new theory explaining the contribution of xylanase in its synergy with glucose oxidase. In this theory glucose oxidase not only catalyses the formation of protein disulfide bonds, but also of AX‐AX crosslinks. The latter negatively affect bread quality. Xylanase corrects for this latter effect by cleaving arabinoxylan complexes and generating small ferulic acid‐containing arabinoxylan fragments interfering with the crosslinking of high‐molecular weight arabinoxylans. Copyright © 2005 Society of Chemical Industry     

Ferulic acid enhances IgE binding to peanut allergens in Western blots

Ferulic acid, a phenolic compound, is known to complex with proteins and peanut allergens. Preliminary studies indicated that ferulic acid could also complex with and inhibit IgE antibodies to peanut allergens in ELISA. However, results from Western blots were quite different. The objective of this study was to report the unexpected finding of IgE binding being enhanced rather than reduced by ferulic acid in Western blot. Ferulic acid, at various concentrations (0–10 mg/ml), was mixed with a pooled plasma (containing IgE antibodies) from peanut-allergic individuals before incubation with a peanut allergen-bound membrane and colorimetric detection of IgE. Results showed that an enhancement of allergen bands or IgE binding, compared to the control, was observed at a ferulic concentration of 10 mg/ml. Compounds with a similar structure, such as caffeic acid and chlorogenic acid, at the same concentration, did not have an enhancing effect on IgE binding. Tests with ferulic acid alone or soy proteins indicated that the enhanced IgE binding was due to the IgE–ferulic complexes and not ferulic acid itself. It was concluded that ferulic acid (10 mg/ml), in combination with IgE, enhanced IgE binding to peanut allergens in Western blots. The finding indicated that ferulic acid can help reduce the time for colour development of protein bands in Western blots.     

Gel-Forming Characteristics of Milk Proteins, 2. Roles of Sulfhydryl Groups and Disulfide Bonds

The gel-forming characteristics of milk proteins were investigated by employing skim milk either nonpreheated or preheated at 80°C, and coagulating them at 70 or 80°C with glucono-delta-lactone. The solubility of each gel in the phosphate buffer (pH 7.0) containing urea and 2- mercaptoethanol was examined. The disulfide bonds played a more important role in the gel coagulated at 80°C from skim milk preheated at 80°C than in the gel coagulated at 70°C from nonpreheated skim milk.The effect of the reduction treatment with 2-mercaptoethanol was more pronounced on preheated skim milk than on nonpreheated skim milk. Sulfhydryl groups and disulfide bonds, which were buried in the molecules of whey proteins in their native state, were rendered accessible following heat treatment at 80°C.The gel prepared from skim milk pretreated with oxidizing agent, hydrogen peroxide (i.e., skim milk has no accessible sulfhydryl groups as a result), or the gel prepared from skim milk pretreated with reducing agent, 2-mercaptoethanol, (i.e., skim milk has few disulfide bonds as a result), displayed weak gel formation. But the gel prepared from the mixture of these skim milks with appropriate ratio displayed higher gel firmness. These findings suggest that intermolecular disulfide bonds are formed by the exchange reaction between sulfhydryl groups and disulfide bonds during gel formation.     

Texture of Chinese water chestnut: Involvement of cell wall phenolics

Chinese water chestnuts (CWC) fail to soften during cooking. This is due to thermal stability of cell wall polymers involved in cell-cell adhesion. Information concerning these polymers was obtained by subjecting CWC tissues to a range of chemical and biochemical treatments designed to cleave selectively cell wall chemical bonds. Neither chelating agents nor weak base (Na₂CO₃, 0·05 M ) facilitated vortex-induced cell separation (VICS) in fresh or canned tissues. However, VICS could be induced after extraction in dilute, cold alkali (0·1 M KOH), dilute hot acid, or a purified, specific endoxylanase. The CWC cell walls also exhibited considerable pH-dependent autofluorescence which originated mainly from ferulic acid and its derivatives. This disappeared during alkali-induced VICS. The results are consistent with the involvement of ferulic acid-containing cell wall hemicelluloses in the thermal stability of cell-cell adhesion and therefore texture in CWC tissues.     

Chemistry and uses of pectin — A review

Pectin is an important polysaccharide with applications in foods, Pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca²⁺ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca²⁺ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low‐methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high‐methoxyl pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors—pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule— influence the gelation of pectin. In the food industry, pectin is used in jams, jellies, frozen foods, and more recently in low‐calorie foods as a fat and/or sugar replacer. In the pharmaceutical industry, it is used to reduce blood cholesterol levels and gastrointestinal disorders. Other applications of pectin include use in edible films, paper substitute, foams and plasticizers, etc. In addition to pectolytic degradation, pectins are susceptible to heat degradation during processing, and the degradation is influenced by the nature of the ions and salts present in the system. Although present in the cell walls of most plants, apple pomace and orange peel are the two major sources of commercial pectin due to the poor gelling behavior of pectin from other sources. This paper briefly describes the structure, chemistry of gelation, interactions, and industrial applications of pectin.     

Enzymic Hydrolysis and Industrial Importance of Barley β-Glucans and Wheat Flour Pentosans

Mixed linkage β-glucane and pentosanes (mainly arabinoxylanes) are the major endosperm cell-wall polysaccharides of barely and wheat respectively. These polysaccharides, although minor components of the whole grain, significantly affect the industrial utilization of these cereals. The modification of barley corns during malting requires the dissolution of the β-glucane in the cell-wall of the starch endosperm. High β-glucane concentration in wort and beer effect the rate of filtration and can also lead to precipitate or gel formation in the final product. In a similar manner, pentosane is thought to cause filtration problems with wheat starch hydrolysates by increasing viscosity and by producing gelatinous precipitate which blocks filters. Ironically, it is this same viscosity building and water binding capacity which is considered to render pentosanes of considerable value in dough development and bread storage (anti-staling functions). In the current paper, some aspects of the beneficial and detrimental effects of pentosanes and β-glucane in the industrial utilization of wheat and barley are discussed. More specifically, enzymic methods for the preparation, analysis and identification of these polysaccharides and for the removal of their functional properties, are described in detail.     

Gel formation in acidified aqueous suspensions of cereal flours

The amounts of gel formed when wheat flours are suspended in 1m acetic acid or in phenol-acetic acid-water (1:1:1, w/v/v) are highly correlated with the total nitrogen contents and the Zeleny sedimentation values of the flours. It is concluded that the Zeleny sedimentation test depends on the formation of this gel. Gel formation in acidified aqueous suspensions is markedly affected by the ionic strength and pH of the suspending medium, but not by non-polar molecules or reagents that react specifically with sulphydryl groups or disulphide bonds. The gel is readily dispersed by ultrasonic treatment and gel formation is prevented completely by the amounts of sodium chloride added to dough during breadmaking.     

Protein molecular interactions involved in the gel network formation of fermented silver carp mince inoculated with Pediococcus pentosaceus

The types of interactions and the proteins involved in the formation of gel network of fermented silver carp mince were investigated. Results showed that the amount of each type of protein interactions varied significantly depending on fermentation time. The content of sulphydryl groups decreased continually with a concomitant increase in disulphide bonds during fermentation. The higher gel strength and more compact fibrous network of fermented silver carp mince corresponded to a higher percentage of hydrophobic interactions, disulphide bonds and non-disulphide covalent bonds. SDS–PAGE showed that the major myofibrillar proteins, particularly myosin heavy chain were involved in the formation of aggregates through hydrophobic interactions and disulphide bonds during fermentation. Furthermore, low molecular weight proteins probably produced by proteolysis were also involved in the formation of gel matrix.     

大豆蛋白凝胶制备及其影响因素的研究进展

大豆作为我国重要的粮食作物之一,具有较高的营养价值。凝胶性作为大豆分离蛋白重要的功能特性备受关注。大豆蛋白在产品中多用作多种配合物如水分子、糖类、脂质以及不稳定小分子活性物质的包埋载体,但大豆蛋白天然凝胶制品存在结构松散、成品率低等问题,极大地限制了其凝胶制品的应用与发展。本文从大豆分离蛋白凝胶形成机理进行解析,并对大豆蛋白构象及组成、多糖、脂质间的相互作用、离子强度等内在影响因素,以及物理、化学、生物等外部因素对凝胶形成产生的影响进行了深入探讨和系统分析,以期对今后大豆蛋白凝胶制品加工与利用提供理论依据。     

大豆分离蛋白与花青素非共价及共价作用对蛋白构象变化的影响

为对比解析大豆分离蛋白-花青素复合体系中非共价/共价作用对蛋白质构象变化规律的影响,以非共价结合（pH?7.4、2?h）和共价交联（pH?9、24?h）2?种作用机制为处理手段,以大豆分离蛋白-花青素复合物为研究对象,采用浊度测定、结合度测定、凝胶电泳分析、荧光光谱和红外光谱法研究复合体系中蛋白质结构变化。结果表明：在大豆分离蛋白-花青素复合体系中,pH?9、24?h条件下样品4～6（20∶1、10∶1、5∶1,m/m）电泳图谱中有大分子衍生物生成,由此说明其形成共价复合物。共价交联处理（pH?9、24?h）样品4～6（20∶1、10∶1、5∶1,m/m）的浊度值低于非共价结合处理（pH?7.4、2?h）样品1～3（20∶1、10∶1、5∶1,m/m）,且复合物4～6中花青素对大豆分离蛋白的亲和能力较强;随复合物中花青素含量的增加,花青素会降低蛋白的荧光强度使色氨酸残基暴露于较为亲水环境中,表明复合样品4～6的荧光猝灭效果明显,共价交联作用强度大于非共价结合作用;在低比例（20∶1,m/m）中,复合物1、4中的蛋白红外光谱吸收强度明显下降,表明复合物中蛋白质二级结构发生改变,且样品4中β-转角及无规则卷曲结构相对含量较高,这表明复合物中花青素共价交联机制对蛋白的解折叠能力较强,结构易展开。     

Pyrolysis-mass spectrometry of the phenolic constituents of plant cell walls

Cell walls of plant parts of maize, barley, Italian ryegrass, wheat bran, lucerne and red clover were subjected to low voltage pyrolysis-mass spectrometry. The ion intensity at m/z 120, which is characteristic of p-coumaric acid, was significantly correlated (r=0.99) with the p-coumaric acid content of the walls; the ion intensity at m/z 150, characteristic of ferulic acid, was present in the spectra of the graminaceous walls. Factor analysis of the pyrolysis-mass spectra indicated that some, at least, of the p-coumaric and ferulic acid constituents of the walls are bound to pentosans, and suggested that not all the aromatic constituents of the walls are bound to polysaccharides.     

血清蛋白质加热凝胶的形成

家畜血液中含有丰富的蛋白质。血液的主要成分——血清或血浆与卵白都有经加热可以形成凝胶的相同性质。食品中蛋白质凝胶的形成能力直接影响着食品的品质。通过对一定浓度的牛和猪的血清蛋白质加热形成凝胶强度的评价,分析了血清中主要蛋白质成分在凝胶形成过程中的作用及其机理。结果表明:牛血清的凝胶强度高于猪血清;牛血清中的白蛋白在血清加热凝胶形成过程中起着重要作用;通过加热血清蛋白,蛋白质分子间的二硫键交联形成凝胶;利用血清蛋白质经加热可以形成凝胶的性质将血清添加到食品中,不仅可以改善食品的品质,而且还可以提高食品中蛋白质的含量。     

Microspectrophotometric characterization of aromatic constituents in cell walls of hard and soft wheats

Cell walls of epidermis, hypodermis, nucellar epidermis, aleurone, and endosperm in hard and soft wheat (Triticum aestivum L) kernels were evaluated for aromatic constituents using ultraviolet (UV) absorption microspectrophotometry. Wheat varieties sampled were soft red winter Caldwell, hard red winter varieties Tam 200 and Karl, and hard red spring varieties Len and Yecora rojo. Spectra of cell walls of epidermis and hypodermis (beeswing cells) suggested larger amounts and a greater degree of polymerization of aromatic constituents in these walls compared to those of other cell types. Results also suggested the presence of ester-linked ferulic acid. Nucellar epidermal walls also had polymerized aromatics and ferulic acid, but amounts appeared to be much less than in the walls of the beeswing cells. UV spectra of aleurone walls suggested that the predominant aromatic was ester-linked ferulic acid; anticlinal walls had substantially more aromatic constituents than outer or inner periclinal walls. Endosperm walls lacked any indication of aromatics by this method. Grain hardness did not appear to be related to cell wall aromatics. UV absorption microspectrophotometry indicated significant variations in wall aromatics of different cell types of wheat grains.