Cold water-extractable pectin in cell walls of plant leaves

When leaves of Cyclea barbata and some other plant species are disintegrated in cold water part of the acidic cell-wall material dissolves. the extracted material is a highly esterified pectin almost free from other polysaccharides; it was identified by its specific optical rotation and by enzymic conversion into D-galacturonic acid. Solubility of such a pure and highly esterified pectin from plant cell walls in cold water seems to occur only in a restricted number of plant species. During storage of the disintegrated tissue for some hours the pectin is gradually de-esterified by pectin esterase resulting in gelation of the suspension. in Indonesia the gel is known as ‘tjintjaoe idjo’ and is used as an ingredient for beverages.     

Simple measurement of phenolic esters in plant cell walls

Phenolic esters may cross-link plant cell wall carbohydrates, strengthening the cell wall and affecting texture of the resulting plant food. In order to measure this effect, it is necessary to obtain some measure of the ester-linked (saponifiable) cinnamic acids in the cell wall. This paper describes a simple procedure which uses ultraviolet absorption as a measure of the ester linked phenolics from a standardized cell wall preparation. HPLC is used to confirm the presence of cinnamic acids in the saponifiable extracts. Carrot and broccoli are used as typical vegetables.     

Cation-exchange capacity of plant cell walls at neutral pH

A new method of measuring the cation-exchange capacity (CEC) of plant materials was developed utilising the tripositive rare earth (RE) elements praseodymium (Pr) or neodymium (Nd). Unlike monovalent cations, the trivalent rare earths become tightly bound to fibre thus decreasing the variability involved with washing. Since the acetate complexes of the rare earths are soluble and relatively stable to hydroxide formation up to pH 7.0, this method can be used to measure CEC of plant materials over the pH range of the gastrointestinal tract. Furthermore, background levels of the RE elements are low in plant tissue. Trivalent Pr and Nd absorb in the visible region of the light spectrum and have the greatest absorptivity of the RE elements. Pr was selected over Nd for this method based upon the binding characteristics of the element. However, Nd may be used if interferences are encountered using Pr. The conditions chosen for optimal binding of Pr to plant materials are as follows: 0.5g samples soaked in 10ml of 0.10M RE acetate, at pH 7.0, for 24h, at 39°C. Coefficients of variation were less than 3.6% for each RE-feedstuff combination examined.     

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.     

Fuel from plant cell walls: recent developments in second generation bioethanol research

As bioethanol from sugarcane and wheat falls out of favour due to concerns about food security, research is ongoing into genetically engineering model plants and microorganisms to find the optimum cell wall structure for the ultimate second generation bioethanol crop. Charis Cook and Alessandra Devoto highlight here the progress made to tailor the plant cell wall to improve the accessibility of cellulose by acting on the regulation, the structure or the relative composition of other cell wall components to ultimately improve saccharification efficiency. They also consider possible side effects of cell wall modification and focus on the latest advances made to improve the efficiency of digestion of lignocellulosic materials by cell wall degrading microorganisms.     

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.     

Rates of degradation of plant cell walls measured with a commercial cellulase preparation

The relationship between the degradability, determined with a commercial cellulase preparation, of the cell walls of various plant parts of Italian ryegrass, maize and red clover can be expressed as Y = A - Be^?k₁^t-Cek₂^t, where Y = percentage of cell walls degraded, t = reaction time, k₁ and k₂ are rates of degradation, and A, B, and C are constants where A = B + C. Degradability of the cell walls of Italian ryegrass or maize could be predicted accurately from the absorbance of the filtrate at λ_max 282-288 or 310-324 nm. Treatment of cell walls of barley straw with 0.1 or 1M sodium hydroxide for 7 or 20 h degraded between 12 and 41% of the walls and led to the release of p-coumaric and ferulic acids, the amount increasing with concentration of alkali and treatment time; the less concentrated alkali released more ferulic than p-coumaric acid. Treatment with the cellulase preparation of the residues from alkali treatment showed that they were almost twice as degradable as the untreated walls.     

Plant cell walls: Supramolecular assemblies

The primary walls of plant cells comprise a large part of our dietary fibre. Their properties depend on the polysaccharides comprising them but also on the manner in which they are interlinked to form the three-dimensional, functional structure of the intact cell wall. This structure is far from homogeneous, but includes local adaptations to withstand local stresses at the cell corners and the margins of intercellular spaces. There is also variation in cell-wall structure at the tissue, organ and species levels. Interlinking of cell-wall polymers by covalent, ionic and hydrogen bonding varies at all these levels and affects the mechanical properties of the cell walls. Cross-linking of pectins in particular, by a variety of covalent as well as non-covalent mechanisms, determines what kind of disruption of the cell wall is necessary to bring them into solution. Solubilisation of pectins has dietary significance in its own right but also leads to an increase in the pore size of the cell wall and hence reduces the extent to which it impedes the entry of enzymes such as α-amylase and the outflow of intracellular macromolecules during the digestion process. The nutritional value of cell walls as ‘dietary fibre’ may then depend on the extent to which the cell walls remain physically intact during the digestion process.     

Aspects of material science in food processing: changes in plant cell walls of fruits and vegetables

 Foods can be regarded as complex, dispersed systems which are normally metastable. Food processing causes state transitions (second-order transitions) when raw materials, food components or food systems are subjected to external stresses. The state transitions occurring during processing are detectable as changes in structure and properties of the investigated systems. The processing of fruits and vegetables is often connected with changes in cell walls. Cell wall materials in dispersed fruit and vegetable systems can be regarded as a model substrate of the dispersed phase. During processing, cell walls undergo modifications in terms of their physical state, macrostructure, microstructure, and composition, as well as structure-dependent changes in their functional and material properties. The interactions and connections (dependencies) between state transitions, and various changes in structure and properties, are very complex and multivariate and are not well understood as yet. For the evaluation of changing material properties during processing, examination of hydration, rheological (external mechanical stress) and thermal (external thermal stress) characteristics is important. The changes occurring during the processing of fruits and vegetables are determined by external factors (especially various mechanical and thermal stresses) and by internal factors. External stress in many cases causes solubilisation of the cell wall, loss of firmness and favours cell separation. Thermal processing increases pectin degradation by β-elimination. Internal factors such as pH and modified ionic strength, e.g. by applying soak solutions, can have an important influence on the changes in the cell wall during processing. So, calcium ions on the one hand can favour cell wall degradation by β-elimination and, on the other hand, after low temperature blanching and de-esterification of the pectin by activated pectin methyl esterase, can contribute to stabilisation of the texture by formation of a calcium-pectin complex. Knowledge about cell wall degradation mechanisms can be markedly improved by studies using model substrates such as pectin, or cell wall materials like the alcohol-insoluble residue and materials with cellular structure. This knowledge has been used to improve the technology used to process fruits and vegetables and to produce products with better properties. Moreover, testing and applying cell wall materials as ingredients for the production of textured foods and potential health-related foods is suggested. Received: 21 July 1998     

Aspects of material science in food processing: changes in plant cell walls of fruits and vegetables

 Foods can be regarded as complex, dispersed systems which are normally metastable. Food processing causes state transitions (second-order transitions) when raw materials, food components or food systems are subjected to external stresses. The state transitions occurring during processing are detectable as changes in structure and properties of the investigated systems. The processing of fruits and vegetables is often connected with changes in cell walls. Cell wall materials in dispersed fruit and vegetable systems can be regarded as a model substrate of the dispersed phase. During processing, cell walls undergo modifications in terms of their physical state, macrostructure, microstructure, and composition, as well as structure-dependent changes in their functional and material properties. The interactions and connections (dependencies) between state transitions, and various changes in structure and properties, are very complex and multivariate and are not well understood as yet. For the evaluation of changing material properties during processing, examination of hydration, rheological (external mechanical stress) and thermal (external thermal stress) characteristics is important. The changes occurring during the processing of fruits and vegetables are determined by external factors (especially various mechanical and thermal stresses) and by internal factors. External stress in many cases causes solubilisation of the cell wall, loss of firmness and favours cell separation. Thermal processing increases pectin degradation by β-elimination. Internal factors such as pH and modified ionic strength, e.g. by applying soak solutions, can have an important influence on the changes in the cell wall during processing. So, calcium ions on the one hand can favour cell wall degradation by β-elimination and, on the other hand, after low temperature blanching and de-esterification of the pectin by activated pectin methyl esterase, can contribute to stabilisation of the texture by formation of a calcium-pectin complex. Knowledge about cell wall degradation mechanisms can be markedly improved by studies using model substrates such as pectin, or cell wall materials like the alcohol-insoluble residue and materials with cellular structure. This knowledge has been used to improve the technology used to process fruits and vegetables and to produce products with better properties. Moreover, testing and applying cell wall materials as ingredients for the production of textured foods and potential health-related foods is suggested.     

Calcium effect on mechanical properties of model cell walls and apple tissue

Bacterial cellulose alone, with pectin added and with both pectin and xyloglucan added were produced as models for plant cell walls. The artificial cell wall materials and natural apple tissue were treated with calcium and then subjected to tests of mechanical properties; a tension test for the artificial cell wall materials and a compression test for the apple tissue. It was found that pectin and xyloglucan had a significant effect on the mechanical properties of artificial cell wall materials, making them more extensible. A high concentration of calcium increased the failure strain and decreased the failure stress of these materials. Treatment of apple tissue with calcium had similar effects on the failure stress and the secant modulus, whereas the differences of failure strain and work to failure resulted in behaviour different from that of the artificial material.     

Evaluation of stabilised diazonium salts for the detection of phenolic constituents of plant cell walls

Sections from laminae of perennial ryegrass and internodes of the annual ryegrass, Lolium termulentum, and red clover were treated with 11 stabilised diazonium salts at pH values between 5 and 9. The walls of cell types which fluoresced blue in ultraviolet radiation in the presence of NH₃, and which gave red colorations with phloroglucinol-HCl and Cl₂-Na₂SO₃ suggesting the presence of lignin, also gave colours with the diazonium salts. After treatment with the salts, lignified walls of grasses gave colours that were of longer wavelength than similar walls of red clover. The most distinct and most intense red colorations were given by p-nitrobenzenediazonium tetrafluoroborate. Lignified walls were either undigested or only partially digested by rumen liquor. In contrast, unlignified walls gave little or no colour with the diazonium salts and were readily digested by the liquor.     

食盐中钙镁含量的测定

本文研究了火焰原子吸收法测定食盐中钙镁含量的方法。结果表明:在一定条件下,钙含量在0.0～20.0μg/ml,镁含量在0.0～2.4μg/ml范围内遵守朗伯比耳定律,方法的精密度(RSD)为2.0%～2.2%。与容量法做对比,方法的相对误差2.3%～4.4%。     

离子色谱法测定水果中阳离子Na+、NH4+、K+、Mg2+、Ca2+的含量

利用离了色谱法测定了五种水果（苹果、梨、橙了、菠萝、草莓）中的阳离了Na^＋、NH4^＋、K^＋、Mg^2＋、Ca^2＋，色谱柱为IonPAC CS12A阳离了交换柱，淋洗液为硫酸，ECD-40电导检测器检测，外标法定量。分析结果表明，五种常见阳离了的线性关系良好，它们的检出限为0．01～0．1mg／L，回收率为93．2％-102．7％，相对标准偏差在0．72％-3．92％之间。该方法具有简单、快速、准确等优点，为检测其它食品中Na^＋、NH4^＋、K^＋、Mg^2＋、Ca^2＋的含量提供了一种有效的方法。     

Mechanical characteristics of artificial cell walls

Artificial plant cell walls were produced from bacterial cellulose and cell wall constituents. The artificial cell walls were stored at low, medium and high relative humidity, and then subjected to micro-mechanical tests. From chemical composition and microstructure analysis it was found that, among all artificial cell wall materials produced, the most representative analogue of natural apple cell wall was based on bacterial cellulose supplemented with xyloglucan and pectin. Uniaxial tensile tests revealed that the different cell wall materials differed in their mechanical properties; increasing the humidity during storage resulted in a decrease in the value of the secant modulus. The cell wall model material obtained may be used for the simulation of the effect of external factors on the physical and chemical properties of cell walls.     

植物细胞培养紫草色素特性的研究

本文研究了PH，糖浓度，温度，光照，紫外线，柠檬酸-磷酸氢二纳缓冲液，柠檬酸，维生素C，氧化剂过氧化氢．还原剂亚硫酸钠等对植物细胞培养生产的紫草色素稳定性的影响。为植物细胞大规模培养紫草色素的生产及利用提供科学依据。