Carbohydrate Matrix Research Articles

STUDIES ON EFFECT OF SHEETING METHODS ON THE EXPANSION OFPAPADSDURING DEEP FAT FRYING USING SCANNING ELECTRON MICROSCOPY

ABSTRACT Scanning electron microscopy (SEM) studies were used to evaluate the distribution/alterations of the cellular matrix of the deep-fat-fried papads, which are traditional food adjuncts of India. Papad is a thin circular sheet made from dough containing blackgram (Phaseolus mungo), common salt and spices in various proportions. The circular sheets are made from the dough by pressing the spherical-shaped dough balls. The method of pressing the dough affects the cellular structure and hence the diametrical expansion of papads during deep fat frying, which is a desirable quality attribute for the papads. In the present study, papads were prepared by employing three different methods of sheeting the dough, viz., by using a wooden roller pin, by using the thumb and by using a mechanical press. Papads produced by these three different methods were deep fat fried, and % expansions were calculated after deep fat frying. Fried papads were subjected to SEM to understand the distribution/alteration of the matrix by different sheeting methods. The SEM micrographs of the thumb-pressed papads showed that they had good distribution of the protein–carbohydrate matrix, thereby achieving the highest diametrical expansion, followed by wooden pin-rolled papads, then by machine-pressed papads. PRACTICAL APPLICATIONS Papads are made commercially at different levels of production, viz., cottage scale, small scale or medium scale. There are different methods of making papad sheets; using a wooden roller pin, thumb pressing or by mechanical pressing are some important methods. The method of making the papad sheet affects the diametrical expansion of papads during deep fat frying, which is a desirable quality attribute commercially. The present study indicates that the thumb pressing method is effective for better expansion. The results have been corroborated with scientific studies using SEM data, which indicated better distribution of protein-carbohydrate matrix. The thumb pressing method of making papad sheets is also helpful for generation of employment in developing countries.

A FAST TRACK TO GREEN GASOLINE

THE PROCESS OF CONVERTING wood chips, agricultural wastes, and other stores of biomass into transportation fuels has captured the imaginations of many scientists. One of these researchers is chemical engineer George W. Huber, whose group at the University of Massachusetts, Amherst, is reporting a selective catalytic pyrolysis process that for the first time permits direct conversion of cellulose into compounds that can be used to make gasoline ( ChemSusChem , DOI: 10.1002/cssc.200800018). A big holdup in biomass conversion is the “recalcitrance” of the plant material—that is, the inability to quickly and economically transform the complex matrix of carbohydrates in plant cell walls directly into useful chemicals and transportation fuels. Investigators are pursuing several physical, chemical, and biological approaches to overcome the recalcitrance problem, including the pyrolysis technique developed by Huber and graduate students Torren R. Carlson and Tushar P. Vispute. Pyrolysis is a well-established meth...

Molecular Packing in Amorphous Carbohydrate Matrixes

The molecular packing of bidisperse matrixes of amorphous carbohydrates consisting of a fractionated maltopolymer supplemented with various amounts of the disaccharide maltose is investigated by combining Positron Annihilation Lifetime Spectroscopy (PALS) with specific volume measurements. The maltopolymer-maltose blends are equilibrated at a range of water activities between 0 and 0.75 at 25 degrees C in order to investigate the effect of water content and carbohydrate molecular weight distribution on the size of the molecular free volume holes in both the glassy and rubbery states. In the rubbery state, the size of the intermolecular holes is only very weakly dependent on the carbohydrate molecular weight, provided that the carbohydrate blends are analyzed at the same water content. In contrast, in the glassy state, significant differences in the size of the free volume holes are observed between the various blends at constant water content. Both the specific volume and the hole volume decrease with increasing maltose content, initially rapidly up to a maltose content of about 40 wt % on total carbohydrate. In addition, we find that the role of water as a plasticizer and matrix constituent is a complex one. At very low water contents, water acts by filling the free volume holes between the carbohydrate molecules. This hole-filling mechanism could well be related to the phenomenon of anti-plasticization observed before. At higher water contents, corresponding generally to water activities above 0.11 at 25 degrees C, water conversely increases the average hole volume in the carbohydrate matrixes, most likely caused by water interfering with the hydrogen bonding between the carbohydrate molecules, leading to a local expansion of the molecular packing.

Sorption of Water by Bidisperse Mixtures of Carbohydrates in Glassy and Rubbery States

Water sorption by bidisperse carbohydrate mixtures consisting of varying ratios of a narrow-molecular-weight distribution maltopolymer and the disaccharide maltose is investigated to establish a quantitative relation between the composition of the carbohydrate system and the water sorption isotherm. The sorption of water is approached from two limiting cases: the glassy state at low water content and the dilute aqueous carbohydrate solution. In the glassy state, the water content at a given water activity decreases with increasing maltose content of the matrix, whereas in the rubbery state it increases with increasing maltose content. The water sorption behavior in the glassy state is quantified using a variety of models, including the often-utilized but physically poorly founded Guggenheim-Anderson-de Boer model, several variants of the free-volume theory of sorption by glassy polymers, and a two-state sorption model introduced in the present paper. It is demonstrated that both the free-volume models and the two-state sorption model, which all encompass the Flory-Huggins theory for the rubbery-state sorption but which differ in their modeling of the glassy-state sorption, provide a physically consistent foundation for the analysis of water sorption by the carbohydrate matrixes.

Real-time assessment of the internal porous structure of cereal materials under high-moisture conditions using 3D MRI and XRT

Ingress of bulk water into porous cereal material causes hydration of the solid matrix accompanied by saturation and swelling of the material. Maintaining crispiness under highmoisture conditions for a certain time is an important feature in terms of consumer perception. Normally macroscopic techniques are used to evaluate crispiness, however these does not provide information about heterogeneity of internal structure changes. Magnetic Resonance Imaging (MRI) which is ideally suited for non-invasive imaging of water as well as water mobilised tissue has found a broad range of applications in different areas, including more recently food science. Appropriate choice of the MRI measurment methods allows the real time visualisation of the effect of hydration in terms of rate and space distribution of structural changes. X-ray Tomography (XRT) on the other hand allows for high resolution 3D visualisation and characterisation (e.g. porosity assessment) of the nonhydrated material before and after certain durations of hydration. The aim of this work was to use MRI to visualise and quantify in real-time the structural changes of the carbohydrate matrix (i.e. swelling) caused by ingress of water and correlate these with structural information from XRT. For this purpose both model and prototype food systems, comprising of phases with contrasting water activity (Aw) were used. To accomplish this work, a RARE measurment method, adapted to the migration rate (time resolution 3.5 min. or better), was used to monitor water redistribution in prototype food systems (i.e. soup inclusions in water) at 25 °C and °60 C. The obtained 3D images with submilimeter resolution allowed the visualisation of the time dependence of the spatial redistribution of moisture, which meant that quantification of the pace of water migration and the extent of matrix swelling could be assessed. In order to understand more fully the role of different water transport mechanisms in carbohydrate matrix structure alteration, a model system composed of a hydrated gel phase (Aw > 0.9) in contact with an initially reasonably dry (Aw = ~0.3) cereal based solid matrix with 3 different porosities, were monitored for 3 days. To properly assess the time dependence of the spatial distribution of the water ingress, the SPI measurment method was used, which allows the visualisation of low and high hydration regimes in various materials. Swelling of the carbohydrate matrix as well as progress of moisture migration through the gas phase were visualised, quantified and correlated with the structural information obtained from XRT measurements. The obtained results demonstrate the potential of the application of the combined MRI/XRT approach to monitor the migration of moisture and accompanying structural changes related to hydration, within porous carbohydrate matrices. The measured migration rates for the model samples with different porosity can be used to predict water redistribution in multiple phase systems in a quantitative manner.

Kinetic study of the release of aroma compounds in different model food systems

Abstract Kinetics of release as a function of time from different model food matrices (mineral water, an oil-in-water emulsion, a carbohydrate matrix and a complex matrix containing lipids and carbohydrates) were measured at 37 °C for four flavour compounds. Carbohydrate matrix and complex matrix were elaborated to have a similar rheological behaviour. Flavour compounds belonging to the strawberry flavour note were chosen: a homologous series of ethyl esters (C4, C6 and C8) and a ketone (C5). The influence of the nature of flavour compounds on the kinetics of release was studied. On the other hand, the influence of the composition of the matrix on the kinetics of release was pointed out. From the kinetics of flavour compounds release, the initial rate of release and the time to reach equilibrium were determined. The measurements of the rate of release during the first five minutes indicated a quickest rate of release during the first thirty seconds.

The influence of pH and digestion with commercial enzymes on calcium adsorption in casabe

SummaryThe Ca2+ binding capacity of a sample of casabe made from cassava (Manihot esculenta) was evaluated by using adsorption isotherms after a digestion process with commercial enzymes. It was found that enzymatic treatment increased the ability of vegetable material to retain calcium and to release endogenous mineral ions as a consequence of possible modifications to the carbohydrate matrix. Untreated casabe did not release mineral ions. pH also influenced the retention of Ca2+: at pH 4.5 release was the main process but adsorption increases with alkalinity up to pH 8.5. The Ca concentrations at which neither adsorption nor release occurred [Ca2+]e were as follows: 5.2 mm (pH 4.5), 3.5 mm (pH 7.1), and 0.63 mm (pH 8.5). The pH effect was explained by an increase in the density of negatively charged functional groups produced by ionization reactions at pH below the point of zero net charge (pHo) which was evaluated by using the Gouy–Chapman double layer model. Values of pHo were 6.4 for raw material and 4.1 after digestion with enzymes. In both cases, the density of positively charged sites below pHo was much higher that the density of negatively charged sites above pHo.

An emerging method for rapid characterization of feed structures and feed component matrix at a cellular leveland relation to feed quality and nutritive value

Feed quality, feed characteristics, nutrient utilization and digestive behaviour are closely related to: (i) total feed composition, (ii) feed intrinsic structures, and (iii) biological component matrix (such as protein to starch matrix, protein to carbohydrate matrix). Conventional “wet” chemical analysis can determine total chemical composition, but fails to detect the feed intrinsic structures and biological component matrix due to destruction of feed samples during the processing for chemical analysis and the “wet” chemical analysis cannot link structural information to chemical information within intact feed tissue. Recently, advanced synchrotron-based Fourier transform infrared (FTIR) microspectroscopy has been developed as a non-destructive and non-invasive structural-chemical analytical technique. This technique can link chemical information to structural information of biological samples within intact tissue within cellular dimensions. It can provide four kinds of information simultaneously: tissue composition, tissue structure, tissue chemistry and tissue environment. However, this novel technique has been found mainly for medical science research, extremely rare for feed science and nutrition research. The objective of this review article was to illustrate synchrotron-based FTIR microspectroscopy as a novel research tool for rapid characterization of feed structures at a cellular level and for detection of chemical features and molecular chemical make-up of feed biological component matrix and nutrient interaction. The emphasis of this article was to show that feed structural-chemical features at a cellular level are closely related to feed characteristics, feed quality and nutritive value in animals. The synchrotron-based technology will provide us with a greater understanding of the plant-animal interface.

Determination of phylloquinone and cholecalciferol encapsulated in granulates formed by melt extrusion

Vitamin K 1 (phylloquinone) and vitamin D 3 (cholecalciferol) play a dominant role in bone metabolism. Both vitamins are sensitive to ultraviolet radiation, oxygen and other environmental influences. For this reason a special extrusion technology was developed, that enables an encapsulation of these sensitive substances in a matrix of carbohydrates and hydrogenated carbohydrates. To exclude decomposition products possibly originating under process conditions quantitative analysis was carried out by HPLC/UV using a modified method based on United States Pharmacopoeia. Under the used chromatographic conditions it has to be possible to separate cis-phylloquinone, trans-phylloquinone and phylloquinone 2,3-oxide, as well as pre-cholecalciferol, cis-cholecalciferol and trans-cholecalciferol. A silica column as stationary phase and a mixture of n-hexane and 1-amyl alcohol as mobile phase were used for quantification. UV detection ensued at 254 nm. A linear relationship between peak area and concentration was found over almost two orders of magnitude for cis-phylloquinone, trans-phylloquinone and cholecalciferol. The detection limits (S/N 3) on column were 0.1 μg for phylloquinone and 0.4 μg for cholecalciferol. Analytical results showed that the vitamins were encapsulated sufficiently in the used carbohydrate matrix and that they were protected against environmental influences. After granulation process all of the samples tested met the pharmacopoeial requirements.

ゲノミクス・プロテオミクスを中心に‐ｏｍｉｃｓへの電気泳動法の応用 グライコミクス

In glycoproteomics, key structural issues, protein identification, locations of glycosylation sites, and the glycosylation site microheterogeneity, should be evaluated in a large number of glycoproteins. To this end, a simple and efficient method, utilizing hydrophilic binding of carbohydrate matrixes such as cellulose and Sepharose to oligosaccharides, was successfully applied to the isolation of glycopeptides from tryptic digests. Both peptide and oligosaccharide structures were elucidated by multiple-stage tandem mass spectrometry (MSn) of the ions generated by matrix-assisted laser desorption/ionization. The method was applied to the analysis of glycan heterogeneities at seven N-glycosylation sites in each of the plasma and cellular fibronectins. In addition, a new O-glycosylation site was identified at Thr279. As a field work using a mass spectrometric strategy including the glycopeptide analysis described above, we have launched a screening study of Congenital Disorders of Glycosylation (CDG). CDG is caused by a defect of one of the nearly one hundred glycosylation or glycosidic enzymes which are involved in the assembly or processing of the N-glycans in endoplasmic reticulum or Golgi apparatus, and thus forms a very large groups of monogenic disorders. Since most glycoproteins are affected, the symptoms and signs of this syndrome is too diverse to diagnose without detailed analysis of the molecular abnormality of glycoproteins. Our activity will delineate most clearly the functional role of glycoprotein glycans in biological systems.

Stability of Alcohol Dehydrogenase (ADH) during a Suspended Droplet Drying and Storage

ABSTRACT The retentions of alcohol dehydrogenase (ADH) activity during drying and storage were investigated at various temperatures and relative humidities for various carbohydrate solutions. The highest retention of ADH activity after drying was obtained for the mixture of trehalose and methyl-β-cyclodextrin. For a single dried droplet, the effects of humidity on the storage stability of ADH were reversed between the trehalose solution and the blend of trehalose and methyl-β-cyclodextrin. However, the addition of methyl-β-cyclodextrin decreased the residual activity of ADH during storage. The carbohydrate matrix structure after drying might influence mainly the storage stability of ADH encapsulated in the mixed carbohydrate of trehalose and methyl-β-cyclodextrin.

Synchrotron Radiation-Induced Formation and Reactions of Free Radicals in Human Acellular Dermal Matrix

The present work characterizes the formation of free radicals in an implantable human acellular dermal tissue (Alloderm, LifeCell Corp., Branchburg, NJ) upon irradiation. The tissue was preserved in a vitreous carbohydrate matrix by freeze-drying. Freeze-dried samples were irradiated using a synchrotron light source, and free radicals generated were investigated using the electron paramagnetic resonance (EPR) technique. At least two free radical populations, with g factors of 1.993 (approximately 43%) and 2.002 (approximately 57%), respectively, were identified in the irradiated tissue. The transformation (reaction) kinetics of free radicals produced was investigated in the presence of nitrogen, oxygen and moisture. The reaction kinetics of free radicals was extremely slow in the nitrogen environment. The presence of oxygen and moisture greatly accelerated free radical reactions in the tissue matrix. The reaction of free radicals could not be described by traditional reaction kinetics. A dispersive kinetics model and a diffusion model were developed to analyze the reaction kinetics in the present study. The dispersive model took into consideration molecular mobility and dispersivity of free radicals in the heterogeneous tissue material. The diffusion model described the radical reaction kinetics as two parallel and simultaneous processes: a first-order fast kinetics mainly on tissue surface and a diffusion-limited slow kinetics in deeper layers of the tissue matrix. Both models described quantitative experimental data well. Further investigation is needed to verify whether any of these two models or concepts describes the inherent radical reaction kinetics in the solid tissue matrix.

Effect of Sodium Chloride, Acetic Acid, and Enzymes on Carotene Extraction in Carrots (Daucus carotaL.)

ABSTRACT: Carrot root cores were cut off longitudinally and treated with NaCl (0.6 and 1.2 M) and/or acetic acid (1.33%, 2.67%, and 4%) solutions. The extractability of the carotenes was estimated. Similarly, carrot cores were also treated with some degrading enzymes (carbohydrases, lipases, and proteases) alone or in combination to study the effect of the tissue rupture or the hydrolysis of possible complexes or interactions between carotenes and other components on the carotene extractability. The results showed that acetic acid increased the extractability of α- and β carotenes up to 99.8% and 94.6%, respectively, at a 4% acid concentration compared with the samples without any treatment. This increase was directly proportional to the acid concentration. An increase in extractability was also observed for NaCl, although the increases were not as high as in the previous case with values of 49% and 41.4% for α- and β-carotenes respectively at a 0.6 M concentration. The study of microstructural changes and extractability revealed that the enzymatic treatments could have broken some carotene complexes and interactions and altered the carbohydrate matrix structure, increasing to a certain extent the extractability of carotenes. It can be concluded then that pickling with 4% acetic acid is a good method to increase the extractability of α- and β-carotenes.

The cellulose/lignin assembly assessed by molecular modeling. Part 1: adsorption of a threo guaiacyl β-O-4 dimer onto a I β cellulose whisker

The assembly of the two major cell wall components, cellulose and lignin, were investigated at the atomistic scale using molecular dynamics simulations. To this end, a molecular model of a cellulose crystal corresponding to the allomorph I β and exhibiting different surfaces was considered to mimic the carbohydrate matrix present in native wood cell wall. The lignin model compound considered here is a threo guaiacyl β-O-4 dimer. The dynamical process of adsorption of the lignin dimer onto the different surfaces of the cellulose crystal was examined. The modes of association between the two constituents were analyzed; energies of adsorption of the dimer are calculated favorable and of the same order of magnitude on all sides of the cellulosic model, suggesting that the deposition of lignin precursors onto cellulose fibers is non-specific from an enthalpic point of view. Interestingly, geometrical characteristics and energetical details of the adsorption are surface-dependent. Computed data have underlined the predominant contribution of van der Waals interactions for adsorption onto the (200) face, as well as the major influence of H-bonding interactions in the dynamical process of adsorption onto (110) and (1-10) faces. A large number of adsorption sites have been identified and a noticeable "flat" geometry of adsorption of the lignin dimer has been observed, as a consequence of the stacking interactions between lignin aromatic rings and C–H groups of cellulose. Importantly, these dispersive interactions lead to a preferential parallel orientation of lignin aromatic rings relative to the cellulose surface, notably on the (200) face. Such a parallel orientation is consistent with previously reported experimental observations.

Carbohydrate Polymers in Amorphous States: An Integrated Thermodynamic and Nanostructural Investigation

The effect of water on the structure and physical properties of amorphous polysaccharide matrices is investigated by combining a thermodynamic approach including pressure- and temperature-dependent dilatometry with a nanoscale analysis of the size of intermolecular voids using positron annihilation lifetime spectroscopy. Amorphous polysaccharides are of interest because of a number of unusual properties which are likely to be related to the extensive hydrogen bonding between the carbohydrate chains. Uptake of water by the carbohydrate matrices leads to a strong increase in the size of the holes between the polymer chains in both the glassy and rubbery states while at the same time leading to an increase in matrix free volume. Thermodynamic clustering theory indicates that, in low-moisture carbohydrate matrices, water molecules are closely associated with the carbohydrate chains. Based on these observations, we propose a novel model of plasticization of carbohydrate polymers by water in which the water dynamically disrupts chains the hydrogen bonding between the carbohydrates, leading to an expansion of the matrix originating at the nanolevel and increasing the number of degrees of freedom of the carbohydrate chains. Consequently, even in the glassy state, the uptake of water leads to increased rates of matrix relaxation and mobility of small permeants. In contrast, low-molecular weight sugars plasticize the carbohydrate matrix without appreciably changing the structure and density of the rubbery state, and their role as plasticizer is most likely related to a reduction of the number of molecular entanglements. The improved molecular packing in glassy matrices containing low molecular weight sugars leads to a higher matrix density, explaining, despite the lower glass transition temperature, the reduced mobility of small permeants in such matrices.

Hydrophilic Affinity Isolation and MALDI Multiple-Stage Tandem Mass Spectrometry of Glycopeptides for Glycoproteomics

In glycoproteomics, key structural issues, protein identification, locations of glycosylation sites, and evaluation of the glycosylation site microheterogeneity should be easily evaluated in a large number of glycoproteins, while mass spectrometry (MS) provides substantial information about individual purified glycoproteins. Considering that structural issues are elucidated by studying glycopeptides and that the tandem MS of a tryptic peptide composed of several amino acid residues is enough for protein identification, construction of an MS-based method handling tryptic glycopeptides would be of considerable benefit in research. To this end, a simple and efficient method, utilizing hydrophilic binding of carbohydrate matrixes such as cellulose and Sepharose to oligosaccharides, was successfully applied to the isolation of tryptic glycopeptides. Both peptide and oligosaccharide structures were elucidated by multiple-stage tandem MS (MS(n)) of the ions generated by matrix-assisted laser desorption/ionization (MALDI), as follows. The MALDI ion trap mass spectrum of a tryptic glycopeptide mixture from N-linked glycoproteins was composed of the [M + H]+ ions of component glycopeptides. Collision-induced dissociation (CID) of the glycopeptide [M + H]+ ion generated saccharide-spaced peaks, with an interval of, for example, 146, 162, and 203 Da, and their fragment ions corresponding to the peptide and peptide + N-acetylglucosamine (GlcNAc) species in the MS2 spectrum. The saccharide-spaced ladder served to outline oligosaccharide structures, which were then selected as precursors for subsequent MS(n) analyses. The peptide or peptide + GlcNAc ions in the MS2 spectrum or the corresponding ions abundant in the MS1 spectrum were subjected to CID for determination of peptide sequences, to identify proteins and their glycosylation sites. The strategy, isolation of glycopeptides followed by MS(n) analysis, efficiently characterized the structures of beta2-glycoprotein I with four N-glycosylation sites and was applied to an analysis of total serum glycoproteins.

Water in Glassy Carbohydrates: Opening It Up at the Nanolevel

Sorption of water by glassy biopolymers and the effects of absorbed water on molecular mobility including plasticization, matrix rearrangements, and diffusion are poorly understood mainly because molecular and structural analyses are scarce. Here, we report the first investigation of the nanostructure of amorphous carbohydrates and the plasticizing effects of water by combining positron annihilation lifetime spectroscopy (PALS) and thermodynamic analysis. Surprisingly, we find that the average volume of the voids between the polymer chains increases with the water content of the matrix while the density of the matrix increases. Consequently, the free volume of the carbohydrate matrix decreases continuously up to the glass transition, primarily by the filling or elimination of the smallest intermolecular voids. We conclude that a so far unknown length scale, the typical size of intermolecular voids, is of fundamental importance in understanding the interaction of water with amorphous carbohydrates and thei...

Protein Translation Inhibition by Stachybotrys Chartarum Conidia with and without the Mycotoxin Containing Polysaccharide Matrix

Recent studies have correlated the presence of Stachybotrys chartarum in structures with SBS. S. chartarum produces mycotoxins that are thought to produce some of the symptoms reported in sick-building syndrome (SBS). The conidia (spores) produced by Stachybotrys species are not commonly found in the air of buildings that have been found to contain significant interior growth of this organism. This could be due in part to the large size of the Stachybotrys spores, or the organism growing in hidden areas such as wall cavities. However, individuals in buildings with significant Stachybotrys growth frequently display symptoms that may be attributed to exposure to the organism's mycotoxins. In addition, Stachybotrys colonies produce a "slime" or polysaccharide (carbohydrate) matrix that coats the hyphae and the spores. The intent of this project was to determine whether the carbohydrate matrix and the mycotoxins embedded in it could be removed from the spores by repeated washings with either aqueous or organic solvents. The results demonstrated that the process of spore washing removed compounds that were toxic in a protein translation assay as compared to spores that were washed with an organic solution, however a correlation between carbohydrate removal during the washing process and the removal of mycotoxins from the spore surface was not observed. These data demonstrated that mycotoxins are not likely to be found exclusively in the carbohydrate matrix of the spores. Therefore, mycotoxin removal from the spore surface can occur without significant loss of polysaccharide. We also showed that toxic substances may be removed from the spore surface with an aqueous solution. These results suggest that satratoxins are soluble in aqueous solutions without being bound to water-soluble moieties, such as the carbohydrate slime matrix.

The effects of lignocellulosic fiber surface area on the dynamics of lignin oxidation and diffusion

A novel preliminary experimental approach was developed to determine the effect of maximizing pulp fiber surface area for the regulation of the oxidation and diffusion of lignin through the carbohydrate matrix. The approach entailed liquid nitrogen freezing of mature black spruce kraft pulp fibers and subsequent mechanical grinding to a fine powder to test the effect of enhanced pulp fiber surface area on the efficiencies of lignin oxidation and lignin diffusion. It was found that the liquid nitrogen ground pulp samples provided higher optical reflectance (brightness) after both oxygen and hydrogen peroxide oxidation, which appears to be from chromophoric (chemical) differences and not light scattering differences as supported by UV/Vis spectroscopy. BET (absorption) experiments indicated a dramatic difference in the surface area of the pulp as a result of the grinding, although no differences existed among the pore sizes between the samples, as determined from SEM experiments. Lignin diffusion experiments demonstrated that differences did exist in the kinetics of lignin diffusion into a bulk solution between a control and liquid nitrogen ground samples. Lignin uptake into bulk solutions was enhanced by the liquid nitrogen/pulp-grinding technique albeit not from chemical changes in the lignin because the subsequent NMR spectra did not point to any major chemical differences as a result of liquid nitrogen freezing and grinding.

Behavior of flavor compounds in model food systems: a thermodynamic study.

Physicochemical parameters, such as hydrophobicity, water solubility, and volatility, of four flavor compounds (ethyl acetate, ethyl butyrate, ethyl hexanoate, and 2-pentanone) were determined. The amount of flavor compounds released from different model matrices (mineral water, purified triolein, an oil-in-water emulsion, a carbohydrate matrix, and a complex matrix containing lipids and carbohydrates) into the gaseous phase was determined at thermodynamic equilibrium, at 37 degrees C, by static headspace gas chromatography. The degree of interaction between the flavor compounds and the matrix components was shown by measuring the percentage retention using the water matrix as the reference. The partition of flavor compounds was principally dependent on their hydrophobicity. Physicochemical interactions that occurred in the different media led to different degrees of flavor retention. An impact of fat on flavor retention was demonstrated when a water matrix and an oil-in-water matrix or carbohydrate and complex matrices were compared. A carbohydrate impact on flavor compound retention was also detected, which was evident even in the presence of lipids.