Degree Of Isomerization Research Articles

Determination of carbohydrates in medicinal plants – comparison of different techniques

Determination of carbohydrates is a challenging and therefore a complex analysis field in phytochemistry. Owing to the high degree of isomerization and epimerization, to the low volatility and to the lack of UV absorbing moieties several analytical techniques cannot be employed without prior modification of target molecules. Additionally within medicinal plants beside carbohydrates several other substances and analytes are present in the produced extract. Aim of this study was the evaluation of different analytical approaches in order to recognize the most suitable technique for qualitative and quantitative analysis of carbohydrates. Focus within the study was placed on thin layer chromatography (TLC), gas chromatography (GC) and a newly developed mass spectrometric method, i.e. matrix free material enhanced laser desorption ionization time of flight mass spectrometry (mf-MELDI-MS) [1]. Samples employed within the study were standards and microwave assisted water extracts from Quercus cortex. TLC was developed using a solvent mixture of butanol:acetic acid:H2O (8:3:2). The visualization of different carbohydrates was performed after reaction with a mixture of acetone – aniline -diphenylamine – phosphoric acid. Mono-, di- and trisaccharides were detected in reference to the carbohydrate standards. Gas chromatography with MS detection has been employed after derivatisation of targets. For di- and tri-saccharides single peaks were obtained, which was not the case for monosaccharides: Glucose for example delivered two signals, but at a constant ratio. Within mf-MELDI-MS from mono- to deca-saccharides clear potassium and sodium adduct signals could be obtained. Evaluation of all three employed techniques clearly proved the performance of mf-MELDI-MS for the qualitative analysis of complex mixtures, as target don't need modification and analysis needs only a few minutes. Beside that GC-MS is suitable for quantitative analysis.

Depression of the Cloud Point of Biodiesel by Reaction over Solid Acids

Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid phase at 125−275 °C using solid acid catalysts. The purpose of this work was to improve the cold flow properties of biodiesel by inhibiting the formation of crystals. Crystallization was analyzed by means of the measurement of the cloud point of the fuel. Tested catalysts were SO42-−ZrO2 and H-mordenite. At a temperature of reaction (Tr) lower than 125 °C, the catalytic activity was negligible. At Tr > 200 °C, the reaction rate was greatly accelerated, but the cetane number was also decreased and the amount of coke deposits was greatly increased. While reacting biodiesel at 150−200 °C, a small decrease (4−6.5 °C) of the cloud point was obtained without a meaningful decrease of the cetane index. Best results were obtained with SO42-−ZrO2 at 125 °C. Isomerization had both positive and negative effects on fuel properties: it reduced the cloud point but also increased the viscosity and decreased the cetane index. Due to the different reactivity between the saturated fraction (estearates, palmitates) and the unsaturated one (linoleates, linolenoates, oleates), an adequate control of the degree of isomerization was only possible by performing a previous fractionation step. A good combination was obtained by reacting the saturates rich fraction at 200 °C over H-mordenite and the unsaturated rich fraction at 150 °C over SO42-−ZrO2. The fuel obtained by mixing both reacted fractions had a cetane index of 49.5 and a cloud point of −2 °C. However, this combined approach yields only a little benefit compared to those obtained with the single reaction over SO42-−ZrO2 at 125 °C.

Diesel-Selective Hydrocracking of an Iron-Based Fischer−Tropsch Wax Fraction (C15−C45) Using a MoO3-Modified Noble Metal Catalyst

Iron-based low-temperature Fischer−Tropsch wax, in the carbon number range of C15−C45, was hydrocracked using an unsulfided Pt/SiO2−Al2O3 catalyst, modified with MoO3. The selective production of diesel having a low cloud point (−18 °C) combined with a high cetane number (71) was achieved. A bench-scale trickle-bed reactor was used to study the effect of operating conditions on product selectivities and yield. The effect of pressure and hydrocarbon chain length on reactivity and diesel properties was studied in particular. Low-pressure operation (3.5 MPa) improved the isoparaffin to n-paraffin ratio for the carbon number range C15−C22 but did not affect the degree of isomerization significantly after C22. The higher pressure of 7.0 MPa suppressed the isomerization and the C23+ percent conversion and improved the diesel selectivity by inhibiting secondary cracking. Increasing the pressure resulted in an overall paraffin reactivity decrease. A maximum in paraffin reactivity at C33 was observed at low-pressure operation, while high-pressure operation resulted in two maxima at C21 and C33. The observed unexpected paraffin reactivity pattern was the consequence of competing concentration and reactivity effects.

Geometrical isomerisation of eicosapentaenoic and docosahexaenoic acid at high temperatures

Concentrates of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were heated at 140–240 °C for 2–8 h under nitrogen. The trans isomers were analysed by gas chromatography-mass spectrometry on a BPX-70 cyanopropyl column. All geometrical isomers of EPA and DHA with one trans double bond were observed. The rate constants (k) for the isomerisation of the all-cis isomers were calculated and found to be higher than previously reported for linoleic acid and α-linolenic acid. Arrhenius plots showed a linear relationship between ln k and the reciprocal absolute temperature above 180 °C. The distribution patterns of isomers with one trans double bond are approximately constant up to a degree of isomerisation of 25%. The degree of isomerisation can therefore be estimated from selected trans peaks.

Synthesis and spectroscopic and structural studies of cross-conjugated dienones derived from cyclic ketones and aromatic aldehydes

Cross-conjugated dienones were synthesized by the reactions of cyclic ketones with two equivalents of aromatic aldehydes under basic conditions. An NMR spectroscopic study and X-ray diffraction analysis demonstrated that all reaction products are formed as E,E isomers. Spontaneous photochemical trans-cis isomerization of cross-conjugated dienones under the scattered light in solution was observed for the first time. The degree of isomerization depends mainly on the nature of the central fragment of the dienone molecule. The previously unknown product of photochemical [2+2]-cycloaddition of 2,5-bis[(E)-(3-pyridyl)methylidene]cyclopentanone was synthesized and characterized by spectroscopic methods and X-ray diffraction. Under the conditions used, only one isomer of the cyclobutane adduct was obtained.

Trans Polyunsaturated Fatty Acid Contents in Brazilian Refined Soybean Oil

This study examined the concentration (mg/g) of trans polyunsaturated fatty acid (TPFA) in five soybean oil brands by gas-liquid chromatography. Tricosanoic acid methyl ester was used as the internal standard. All samples analyzed presented trans 18:2 fatty and trans 18:3 acids in detectable amounts. The concentration of TPFA ranged from 5.8 to 30.2 mg/g, with a mean concentration value of 18.4 mg/g. Trans 18:3 fatty acids had the highest TPFA group concentrations, which ranged from 3.9 to 16.3 mg/g. The main isomer of this group presented the 9c, 12c, 15t configuration. For trans 18:2 fatty acids, concentrations ranged from 1.9 to 14.0 mg/g with a mean value of 8.1 mg/g. Alpha-linolenic acid (all cis) concentrations ranged from 30.7 to 60.6 mg/g and their degree of isomerization ranged from 6.0 to 31.5, indicating that the deodorization process varies from one producer to another. From per capita consumption of soybean oil brands in Brazil and their TPFA concentrations, it is possible to conclude that their contribution to the average TPFA intake per person in Brazil is 0.4 g/d.

Tomato pulp as source for the production of lycopene powder containing high proportion of cis-isomers

Cis-isomers of lycopene has been demonstrated to possess higher biological activity than its all-trans form. The objectives of this study were to compare the extraction efficiency and degree of isomerization of lycopene by employing supercritical carbon dioxide (SCD) and solvents, as well as process the lycopene extract into powder containing high proportion of cis-isomers from tomato pulp as source. Results showed that a high yield of lycopene was achieved by SCD at 350 bar and 70 °C, with cis-isomers making up 41.4% of total lycopene. However, with temperature at 80 and 90 °C, the maximum isomerization was accomplished, and cis-lycopene constituted 51.0 and 53.8% of total lycopene, respectively. For solvent extraction, the highest yield of all-trans-lycopene was attained by ethanol–hexane (4/3 v/v) at 25 and 50 °C, whereas the maximum isomerization (47.0% cis-lycopene) occurred at 75 °C. A powder product containing 34.5% cis-isomers of lycopene was obtained by spray-drying, and the total amount of lycopene in spray-dried powder was much greater than that in freeze-dried powder. The maximum yield of lycopene in the powder product could be obtained through processing by adding sodium alginate to the eluate directly after SCD extraction and open-column chromatography with formation of 41.4% cis-lycopene. The method developed in this study may be used for possible commercial production of highly active lycopene powder.

Fatty acid profiling of lipid classes by silica rod TLC-thermally assisted hydrolysis and methylation–GC/MS

Advances towards the coupling of thin layer chromatography (TLC) Chromarods to gas chromatography/mass spectrometric (GC/MS) analysis were accomplished by introducing an intact TLC silica-coated rod (15 cm) into a vertical furnace pyrolyzer coupled to a GC/MS instrument. Using this technique, a fatty acid profile corresponding to the neutral and polar fraction of a lipid extract previously separated by TLC was obtained. The fatty acids were analyzed directly off the TLC rod, as their methyl derivatives were obtained following thermally assisted hydrolysis methylation (THM) in the presence of trimethylsulfonium hydroxide (TMSH). The results show that the THM reaction is successful on lipids that are adsorbed on the silica surface. Using lipid standards, differences in the fatty acid yield for the THM reaction of phospholipids (PL), triacylglycerides (TAG) and free fatty acids (FFA) were observed. Compared to conventional TMSH/lipid solution analysis, there was a significant decrease in the degree of isomerization for polyunsaturated fatty acids (PUFA) using the TMSH/silica-supported reaction, when a relatively high TMSH/lipid molar ratio (>2500) is used. The fatty acid profile for a marine (cold water) lipid sample using silica-supported THM compared well with results obtained by conventional lipid extraction followed by BF 3–methanol esterification. This study's success of in situ analysis of intact chromatographic bands illustrates the strong potential for TLC–GC/MS.

Quantification of the isomerization of Asp residue in recombinant human αA-crystallin by reversed-phase HPLC

A method for determining the isomerization of Asp residues in proteins is described and demonstrated by quantifying the isomerization of Asp 151 in recombinant human αA-crystallin. First, four types of dodecapeptide fragment ( 146IQTGLD 151ATHAER 157) in which the Asp residue was either l-Asp, d-Asp, l-isoAsp or d-isoAsp were synthesized, and RP-HPLC conditions were established for their separation. Next, the Asp 151-containing peptide fragments isolated from the tryptic hydrolysate of recombinant αA-crystallin were analyzed under these conditions. New peaks, the retention times of which were the same as those of peptides containing d-Asp, l-isoAsp and d-isoAsp, were generated when αA-crystallin was incubated for 140 days at 37 °C. An amino acid composition, amino acid sequence, and enantiomeric analysis revealed that two peaks with retention times identical to those of peptides containing l-isoAsp and d-isoAsp represented dodecapeptide fragments containing l-isoAsp 151 and d-isoAsp 151, respectively. RP-HPLC analysis under other condition suggested that the peak with retention time identical to that of peptide containing d-Asp represented dodecapeptide fragments containing d-Asp 151. The present method does not require acid hydrolysis, which generates further isomerization products as artifacts, and thus make possible the sensitive quantification of each type of Asp isomer individually at a specific site in a protein. In our analysis of the Asp 151 residue in human αA-crystallin, the degree of isomerization from l-Asp to d-Asp can be determined to a level as low as 0.3%.

Surface collisions of the acetonitrile molecular ion: evidence for isomerization of CD3CN[rad]+ to the ketenimine cation CD2CND[rad

Reactions induced by the impact of acetonitrile and deuterated acetonitrile molecular ions on a hydrocarbon-covered stainless steel surface were investigated using a recently constructed tandem mass spectrometer (BESTOF). Mass spectra of product ions formed were recorded for projectile collision energies in the range of about 5–70eV. Both, simple dissociations of the projectile ion and chemical reactions involving H-atom transfer from the surface material (followed by subsequent dissociation of the protonated projectile ion formed) were observed. In particular, formation of CD2H+ and CD3+ via dissociation of the surface-protonated deuterated acetonitrile ion CD3CNH+ and the collision energy dependence of their relative abundance indicate substantial degree of isomerization of the acetonitrile molecular radical cation CD3CN+ to the ketenimine ion CD2CND+. The isomerization seems to take place upon electron impact ionization of the acetonitrile molecule in the ion source preceding the tandem mass spectrometer.

Positional and geometric isomer separation of FAME by comprehensive 2-D GC.

The technique of comprehensive GC (GC x GC) was applied to the analysis of a standard mixture of FAME. The methodology involved the use of two directly coupled capillary GC columns providing different retention mechanisms, with a pulsing modulator located near their union. The first column was chosen to elute analytes based on b.p. variations, and the second column was based on polarity. Thus, the separation in the two dimensions was orthogonal, since solutes delivered simultaneously to the second column had similar b.p., and the second column separated these primarily on their differentiating mechanisms of polarity. Greater sensitivity of detection and narrower peak widths were obtained; here, peak response increases of about 20-fold were obtained, with pulsed peak widths of about 150 ms. Peaks were displayed in a 2-D contour plot to allow the complexity of the compounds to be seen and their b.p. and polarity properties to be readily recognized. Chromatographic separation of geometric and positional isomers of FAME in the 2-D space is possible. Since retention can be related to the degree and manner of unsaturation and isomerization, and as peak positions are highly reproducible in the 2-D retention map, this is a useful aid for component identification in the absence of appropriate standards. In this work, two column combinations were used to examine the effects of polarity changes on component separation. Improved quantitation based on FID area measurement was demonstrated. A sample of marine oil gave 49 resolved, identified peaks, with at least an additional 20 peaks resolved but not identified.

MODELLING OF THE SOLVENT-DEOILING PROCESS OF WAXES BY CONTINUOUS THERMODYNAMICS

ABSTRACT Industrial waxes as petroleum slack waxes are multicomponent mixtures of mainly paraffinic species. Usually, for application the oily components of the waxes are undesired. Therefore, separation processes are needed which, in some cases, base on a solvent-deoiling process. Modelling such a process is the aim of this paper. For this purpose the solid–liquid equilibrium of a wax–solvent system is considered. To take into account the polydispersity of the wax continuous thermodynamics is applied. We assume the wax to consist of n-alkanes and of non-n-alkanes including all the other types of paraffinic species. Corresponding to that, the composition of both types of alkanes is described by separate Gaussian distributions with respect to the number of carbon atoms. The model requires information about how the molar enthalpy and entropy of fusion for both kinds of alkanes depend on the number of carbon atoms. Restricting to the interesting range 20–50 of the number of carbon atoms we assume linear relations The lower values of the enthalpy and entropy of fusion for the non-n-alkanes compared to those of the n-alkanes are described by the so-called degree of isomerization and cyclization. This quantity correlates to the refraction index that is easy available. The model needs only one interaction parameter to fit. We show experimental and calculated results for three systems consisting of a slack wax and a solvent mixture of 1,2-dichloroethane and toluene. The model is able to describe reasonably the enrichment of n-alkanes for the deoiled wax and the opposite for the the oily phase.

Influence of isomerisation on the growth inhibitory effects and cellular activity of 13- cis and all- trans retinoic acid in neuroblastoma cells

Treatment with 13- cis retinoic acid (13- cis RA) has been shown to significantly improve the clinical outcome of children with high-risk neuroblastoma. Despite the large number of studies investigating the cellular effects of retinoids in neuroblastoma cells, the influence of RA isomerisation and the factors that determine the extent of RA isomerisation and uptake are unknown. The aim of this study was to establish the extent of extra- and intracellular isomerisation of 13- cis RA and all- trans retinoic acid (ATRA) in neuroblastoma cell lines, and to investigate the influence of isomerisation on their growth inhibitory effects and on the regulation of expression of cellular retinoic acid binding protein II (CRABP II) and RAR-β. Limited extracellular isomerisation was observed up to 72 hr after incubation of four neuroblastoma cell lines with 10 μM 13- cis RA or ATRA. The retinoic acid isomer present initially in the medium accounted for >75% of extracellular retinoid exposure. By contrast, incubation with 13- cis RA resulted in intracellular levels of ATRA comparable to those of 13- cis RA. This degree of intracellular isomerisation was not observed after ATRA incubations, with 13- cis RA accounting for <10% of total intracellular retinoids. No differences were observed in the sensitivity of three N-type neuroblastoma cell lines to either 13- cis RA ( ic 50: 11.2–13.9 μM) or ATRA ( ic 50: 12.9–14.4 μM), despite 10-fold differences in intracellular retinoid levels. A decrease in sensitivity to 13- cis RA ( ic 50=137 μM), as compared to ATRA ( ic 50=41 μM), was observed in the S-type cell line SH S EP. RAR-β was induced in a dose-dependent manner in SH SY 5Y cells following incubation with ATRA, whereas a weaker and delayed induction was observed with 13- cis RA. Similarly, incubation with ATRA resulted in a greater induction of CRABP II in these cells. In summary, these results indicate either an intracellular conversion of 13- cis RA to ATRA or a selective uptake of ATRA and suggest that this may mediate the differential activity of 13- cis RA in neuroblastoma cell subtypes.

Deodorization of vegetable oils: Prediction of trans polyunsaturated fatty acid content

AbstractKinetics of the formation of trans linoleic acid and trans linolenic acid were compared. Pilot plant‐scale tests on canola oils were carried out to validate the laboratory‐scale kinetic model of geometrical isomerization of polyunsaturated fatty acids described in our earlier publication. The reliability of the model was confirmed by statistical calculations. Formation of the individual trans linoleic and linolenic acids was studied, as well as the effect of the degree of isomerization on the distribution of the trans fatty acid isomers. Oil samples were deodorized at temperatures from 204 to 230°C from 2 to 86 h. Results showed an increase in the relative percentage of isomerized linolenic and linoleic acid with an increase in either the deodorization time or the temperature. The percentage of trans linoleic acid (compared to the total) after deodorization ranged from &lt;1 to nearly 6%, whereas the percentage of trans linolenic acid ranged from &lt;1 to &gt;65%. Applying this model, the researchers determined the conditions required to produce a specially isomerized oil for a nutritional study. The practical applications of these trials are as follows: (i) the trans fatty acid level of refined oils can be predicted for given deodorization conditions, (ii) the conditions to meet increasingly strict consumer demands concerning the trans isomer content can be calculated, and (iii) the deodorizer design can be characterized by the deviation from the theoretical trans fatty acid content of the deodorized oil.

Multiple conformations of PEVK proteins detected by single-molecule techniques.

An important component of muscle elasticity is the PEVK region of titin, so named because of the preponderance of these amino acids. However, the PEVK region, similar to other elastomeric proteins, is thought to form a random coil and therefore its structure cannot be determined by standard techniques. Here we combine single-molecule electron microscopy and atomic force microscopy to examine the conformations of the human cardiac titin PEVK region. In contrast to a simple random coil, we have found that cardiac PEVK shows a wide range of elastic conformations with end-to-end distances ranging from 9 to 24 nm and persistence lengths from 0.4 to 2.5 nm. Individual PEVK molecules retained their distinctive elastic conformations through many stretch-relaxation cycles, consistent with the view that these PEVK conformers cannot be interconverted by force. The multiple elastic conformations of cardiac PEVK may result from varying degrees of proline isomerization. The single-molecule techniques demonstrated here may help elucidate the conformation of other proteins that lack a well-defined structure.

Origin of prist-1-ene and prist-2-ene in kerogen pyrolysates

The principal isoprenoid hydrocarbons in flash pyrolysates from immature kerogens are prist-1-ene and, to a lesser extent, prist-2-ene. The precise origin of these compounds is still a matter of debate. Chemical degradation experiments performed on a sulfur-rich kerogen in this study show that at least two precursors can generate pristenes during pyrolysis of sulfur-rich kerogens: ether-bound precursors, probably tocopherols, and a sulfur-bound precursor. From pyrolysis experiments performed on mixtures of isolated kerogens with different clay minerals, it is concluded that prist-2-ene is likely formed by the double-bond isomerization of prist-1-ene. This isomerization of prist-1-ene into prist-2-ene depends on the amount of protons available for the formation of the intermediate carbonium ion. These protons can be derived from acidified aluminosilicates (e.g. the clay minerals montmorillonite or kaolinite) in the rock or from inorganic acids (e.g. HI, HCl). The degree of isomerization depends on the amount of protons available relative to the total organic carbon content.

Racemization and isomerization of type I collagen C-telopeptides in human bone and soft tissues: assessment of tissue turnover

Urinary excretion of the type I collagen C-telopeptide (CTx) has been shown to be a sensitive index of the rate of bone resorption. The human type I collagen sequence A(1209)HDGGR(1214) of CTx can undergo racemization of the aspartic acid residue Asp(1211) and isomerization of the bond between this residue and Gly(1212). These spontaneous non-enzymic chemical reactions takes place in vivo in bone, and the degree of racemization and isomerization of CTx molecules may be an index of the biological age and the remodelling of bone. The aim of the present study was to investigate the degree of racemization and isomerization of type I collagen in human connective soft tissues, in order to estimate the rate of collagen turnover in adult tissues and compare it with that of bone. We also performed a systematic evaluation of the pyridinium cross-link content in adult human tissues. Using antibodies raised against the different CTx forms, we found that bone and dermis are the tissues that show most racemization and isomerization. The type I collagen of arteries, lung, intestine, kidney, skeletal muscle and heart shows significantly less racemization and isomerization than that of bone, suggesting that these soft tissues have a faster turnover than bone. We also found that pyridinoline and, to a lesser degree, deoxypyridinoline are distributed throughout the different tissues investigated. Because bone type I collagen is characterized by a high degree of both racemization/isomerization and deoxypyridinoline cross-linking, the concomitant assessment of these two post-translational modifications is likely to result in a highly specific marker of bone resorption.

Lycopene in Tomatoes: Chemical and Physical Properties Affected by Food Processing

ABSTRACT: Lycopene is the pigment principally responsible for the characteristic deep-red color of ripe tomato fruits and tomato products. It has attracted attention due to its biological and physicochemical properties, especially related to its effects as a natural antioxidant. Although it has no provitamin A activity, lycopene does exhibit a physical quenching rate constant with singlet oxygen almost twice as high as that of β-carotene. This makes its presence in the diet of considerable interest. Increasing clinical evidence supports the role of lycopene as a micronutri-ent with important health benefits, because it appears to provide protection against a broad range of epithelial cancers. Tomatoes and related tomato products are the major source of lycopene compounds, and are also considered an important source of carotenoids in the human diet. Undesirable degradation of lycopene not only affects the sensory quality of the final products, but also the health benefit of tomato-based foods for the human body. Lycopene in fresh tomato fruits occurs essentially in the all-trans configuration. The main causes of tomato lycopene degradation during processing are isomerization and oxidation. Isomerization converts all-trans isomers to cis-isomers due to additional energy input and results in an unstable, energy-rich station. Determination of the degree of lycopene isomerization during processing would provide a measure of the potential health benefits of tomato-based foods. Thermal processing (bleaching, retorting, and freezing processes) generally cause some loss of lycopene in tomato-based foods. Heat induces isomerization of the all-trans to cis forms. The cis-isomers increase with temperature and processing time. In general, dehydrated and powdered tomatoes have poor lycopene stability unless carefully processed and promptly placed in a hermetically sealed and inert atmosphere for storage. A significant increase in the cis-isomers with a simultaneous decrease in the all-trans isomers can be observed in the dehydrated tomato samples using the different dehydration methods. Frozen foods and heat-sterilized foods exhibit excellent lycopene stability throughout their normal temperature storage shelf life.Lycopene bioavailability (absorption) can be influenced by many factors. The bioavailability of cis-isomers in food is higher than that of all-trans isomers. Lycopene bioavailability in processed tomato products is higher than in unprocessed fresh tomatoes. The composition and structure of the food also have an impact on the bioavailability of lycopene and may affect the release of lycopene from the tomato tissue matrix. Food processing may improve lycopene bioavailability by breaking down cell walls, which weakens the bonding forces between lycopene and tissue matrix, thus making lycopene more accessible and enhancing the cis-isomerization. More information on lycopene bioavailability, however, is needed. The pharmacokinetic properties of lycopene remain particularly poorly understood. Further research on the bioavalability, pharmacology, biochemistry, and physiology must be done to reveal the mechanism of lycopene in human diet, and the in vivo metabolism of lycopene.Consumer demand for healthy food products provides an opportunity to develop lycopene-rich food as new functional foods, as well as food-grade and pharmaceutical-grade lycopene as new nutraceutical products. An industrial scale, environmentally friendly lycopene extraction and purification procedure with minimal loss of bioactivities is highly desirable for the foods, feed, cosmetic, and pharmaceutical industries. High-quality lycopene products that meet food safety regulations will offer potential benefits to the food industry.

Lycopene in Tomatoes: Chemical and Physical Properties Affected by Food Processing

Lycopene is the pigment principally responsible for the characteristic deep-red color of ripe tomato fruits and tomato products. It has attracted attention due to its biological and physicochemical properties, especially related to its effects as a natural antioxidant. Although it has no provitamin A activity, lycopene does exhibit a physical quenching rate constant with singlet oxygen almost twice as high as that of β-carotene. This makes its presence in the diet of considerable interest. Increasing clinical evidence supports the role of lycopene as a micronutri-ent with important health benefits, because it appears to provide protection against a broad range of epithelial cancers. Tomatoes and related tomato products are the major source of lycopene compounds, and are also considered an important source of carotenoids in the human diet. Undesirable degradation of lycopene not only affects the sensory quality of the final products, but also the health benefit of tomato-based foods for the human body. Lycopene in fresh tomato fruits occurs essentially in the all-trans configuration. The main causes of tomato lycopene degradation during processing are isomerization and oxidation. Isomerization converts all-trans isomers to cis-isomers due to additional energy input and results in an unstable, energy-rich station. Determination of the degree of lycopene isomerization during processing would provide a measure of the potential health benefits of tomato-based foods. Thermal processing (bleaching, retorting, and freezing processes) generally cause some loss of lycopene in tomato-based foods. Heat induces isomerization of the all-trans to cis forms. The cis-isomers increase with temperature and processing time. In general, dehydrated and powdered tomatoes have poor lycopene stability unless carefully processed and promptly placed in a hermetically sealed and inert atmosphere for storage. A significant increase in the cis-isomers with a simultaneous decrease in the all-trans isomers can be observed in the dehydrated tomato samples using the different dehydration methods. Frozen foods and heat-sterilized foods exhibit excellent lycopene stability throughout their normal temperature storage shelf life.Lycopene bioavailability (absorption) can be influenced by many factors. The bioavailability of cis-isomers in food is higher than that of all-trans isomers. Lycopene bioavailability in processed tomato products is higher than in unprocessed fresh tomatoes. The composition and structure of the food also have an impact on the bioavailability of lycopene and may affect the release of lycopene from the tomato tissue matrix. Food processing may improve lycopene bioavailability by breaking down cell walls, which weakens the bonding forces between lycopene and tissue matrix, thus making lycopene more accessible and enhancing the cis-isomerization. More information on lycopene bioavailability, however, is needed. The pharmacokinetic properties of lycopene remain particularly poorly understood. Further research on the bioavalability, pharmacology, biochemistry, and physiology must be done to reveal the mechanism of lycopene in human diet, and the in vivo metabolism of lycopene.Consumer demand for healthy food products provides an opportunity to develop lycopene-rich food as new functional foods, as well as food-grade and pharmaceutical-grade lycopene as new nutraceutical products. An industrial scale, environmentally friendly lycopene extraction and purification procedure with minimal loss of bioactivities is highly desirable for the foods, feed, cosmetic, and pharmaceutical industries. High-quality lycopene products that meet food safety regulations will offer potential benefits to the food industry.

THERMODYNAMIC FUNCTIONS OF THE SOLID-LIQUID TRANSITION OF HYDROCARBON MIXTURES

ABSTRACT The dependences of the melting temperature and the enthalpy of fusion on the composition are the essential factors for modelling precipitation and solubility of solid hydrocarbons in crude oils and crude oil products. Long-chain iso-alkanes and cyclic alkanes must be considered besides of n-alkanes. Therefore a degree of isomerization and cyclization was defined using the refractive index and the carbon number. The melting temperatures and the enthalpies of fusion of different n-alkanes and fractions of crude oil were determined by differential scanning calorimetry. Both parameters can be correlated with the degree of isomerization and cyclization by a quadratic fuction.