Development of an advanced derivatization protocol for the unambiguous identification of monosaccharides in complex mixtures by gas and liquid chromatography

The separation and analysis of complex monosaccharide mixtures is highly challenging and requires typically carefully selected derivatization procedures to avoid changes in the sample composition. Here we present in a comparative study several single- and two-step derivatization approaches for LC and GC separations using a set of reference compounds ranging from C1 building block such as formaldehyde to C6 monosaccharides. Separation conditions have been optimized resulting in the simultaneous separation of 15 unbranched aldoses. By parallel derivatization using hydroxylamine hydrochloride (HACl)/ N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and O-ethylhydroxylamine hydrochloride (EtOx)/ N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and comparative GC measurements we developed a protocol for the unambiguous identification and separation of aldoses, ketoses, alditols and aldonic acids, which commonly occur in complex sugar mixtures as reaction by-products or decomposition products. In particular this procedure helps to deconvolute overlapping analytes and facilitates quantification. Additionally, the method presented here has been investigated in regard to storage life, detection limits, quantification and MS analysis. The broad applicability of this method to different sample matrices is shown for the analysis of food samples and complex aldol reaction mixtures in the formose reaction, which is of great relevance in the context of the origin of life.

Thiazolidine Peracetates: Carbohydrate Derivatives that Readily Assign cis-, trans-2,3-Monosaccharides by Gas Chromatography-Mass Spectrometry Analysis

A novel group of carbohydrate derivatives is described that uniquely assign cis/ trans-2,3-aldose stereoisomers at low nanomolar concentrations. Aldopentoses, aldohexoses, or component aldoses from hydrolysis of polysaccharides or oligosaccharides react with cysteamine in pyridine to give quantitative formation of thiazolidines, which are subsequently peracetylated in a one-pot reaction. The nonpolar thiazolidines peracetate (TPA) derivatives are analyzed by gas chromatography and electron impact mass spectrometry (GC/EI-MS), each aldose giving rise to two TPA geometric isomers. The quantitative ratio of these diastereomers is dependent upon whether the parent monosaccharide is cis-2,3-(Rib, Lyx, Man, All, Gul, and Tal), or trans-2,3-aldose (Xyl, Ara, Glc, Gal, Ido, and Alt). TPAs generate observed EI-MS fragment ions characteristic of C1-C2 and C3-C4 bond cleavage of the parent sugars. This has been used to estimate the extent of metabolic labeling of microbial cell-wall carbohydrates, especially into the defining anomeric carbons and during aldolase / ketolase -catalyzed rearrangements.

Synthesis of Prebiotic Caramels Catalyzed by Ion-Exchange Resin Particles: Kinetic Model for the Formation of Di-d-fructose Dianhydrides

Caramel enriched in di-d-fructose dianhydrides (DFAs, a family of prebiotic cyclic fructodisaccharides) is a functional food with beneficial properties for health. The aim of this work was to study the conversion of fructose into DFAs catalyzed by acid ion-exchange resin, in order to establish a simplified mechanism of the caramelization reaction and a kinetic model for DFA formation. Batch reactor experiments were carried out in a 250 mL spherical glass flask and afforded up to 50% DFA yields. The mechanism proposed entails order 2 reactions that describe fructose conversion on DFAs or formation of byproducts such as HMF or melanoidines. A third order 1 reaction defines DFA transformation into fructosyl-DFAs or fructo-oligosaccharides. The influence of fructose concentration, resin loading and temperature was studied to calculate the kinetic parameters necessary to scale up the process.

Carbohydrate Composition Analysis in Xylem

Gas chromatography-mass spectrometry (GC-MS) is a widely applied technique in carbohydrate composition analysis due to high accuracy and repeatability. As cell walls are the major carbohydrate pool in xylem tissues, the measurement of carbohydrate composition essentially constitutes an analysis of wall residues. Here, we describe the method for quantification of the contents of several common neutral monosaccharides and cellulose, the major components of cell walls in poplar xylem tissues, by GC-MS. The procedures for extraction of cell wall residues from xylem, generation of alditol derivatives, subsequent further separation on gas chromatograph, and detection by mass spectrometer are included.

Rhodotorula taiwanensis MD1149 produces hypoacetylated PEFA compounds with increased surface activity compared to Rhodotorula babjevae MD1169

Biosurfactants have several desirable characteristics in the industrial sector: detergency, antimicrobial effects, skin hydration, and emulsibility. Several yeast glycolipids are currently being utilized in these capacities: sophorolipids, ustilagic acid, and mannosylerythritol lipids (MELs). An emerging class of glycolipids, termed polyol esters of fatty acids (PEFA), have recently been reported for Rhodotorula babjevae, a basidiomycetous yeast species that secretes hyperacetylated congeners of PEFA (typically with 3–6 acetylation modifications). While screening Rhodotorula species for surfactant production, we identified a new environmental isolate identified as Rhodotorula taiwanensis MD1149 that dropped the surface tension of the liquid medium, indicating that it produced a potent biosurfactant. Acid depolymerization of the purified biosurfactants, followed by gas chromatography-mass spectrometry (GC-MS) analysis revealed that the biosurfactants were composed of PEFA compounds composed mainly of mannitol and arabitol esters of 3-hydroxy fatty acid, 3-methoxy fatty acid, and fatty acids with a single double bond; chain lengths were mainly C16 and C18. Liquid chromatography-mass spectrometry (LC-MS) confirmed the predicted accurate mass of these compounds. Interestingly, PEFA compounds produced by Rhodotorula taiwanensis MD1149 were more surface active due to their hypoacetylation profile (0–4 acetylation modifications) compared to Rhodotorula babjevae MD1169. These disparate surface active properties, based on acetylation, change the hydrophilic-lipophilic balance (HLB) of these compounds, and their potential utility within industrial applications.

Do linden trees kill bees? Reviewing the causes of bee deaths on silver linden (Tilia tomentosa)

For decades, linden trees (basswoods or lime trees), and particularly silver linden (Tilia tomentosa), have been linked to mass bee deaths. This phenomenon is often attributed to the purported occurrence of the carbohydrate mannose, which is toxic to bees, in Tilia nectar. In this review, however, we conclude that from existing literature there is no experimental evidence for toxicity to bees in linden nectar. Bee deaths on Tilia probably result from starvation, owing to insufficient nectar resources late in the tree's flowering period. We recommend ensuring sufficient alternative food sources in cities during late summer to reduce bee deaths on silver linden. Silver linden metabolites such as floral volatiles, pollen chemistry and nectar secondary compounds remain underexplored, particularly their toxic or behavioural effects on bees. Some evidence for the presence of caffeine in linden nectar may mean that linden trees can chemically deceive foraging bees to make sub-optimal foraging decisions, in some cases leading to their starvation.

Development of capillary liquid chromatography: A personal perspective

This is a historical account on the development of capillary LC from its beginning to the present day. The first investigations into the viability of capillary LC date back to the late 1970s, a decade after the pioneering efforts in HPLC. The drastically reduced column dimensions were required to counter the slow solute diffusion in liquids. There were numerous instrumental difficulties with sample introduction and detection in the picoliter or even femtoliter volumes. High-efficiency separations were needed in the analysis of complex biological mixtures. Miniaturization brought distinct advantages in spectroscopic and electrochemical detection. Since the 1980s, column technologies underwent significant changes: (a) from glass-drawn microcapillaries to slurry-packed, small-diameter fused silica columns; and (b) in microcapillaries packed alternatively with sub-2-μm particles or monoliths. The viability of LC-MS combination has dramatically promoted the use of small-diameter capillaries. Through "omics technologies", capillary LC/tandem MS accounts for most applications in proteomics, glycomics and metabolomics.

Dietary docosahexaenoic acid supplementation prevents the formation of cholesterol oxidation products in arteries from orchidectomized rats

Testosterone deficiency has been correlated with increased cardiovascular diseases, which in turn has been associated with increased oxidative stress. Several studies have considered cholesterol oxidation products (COPs) as oxidative stress biomarkers, since some of them play pro-oxidant and pro-inflammatory roles. We have previously described the cardioprotective effects of a dosahexaenoic acid (DHA) supplemented diet on the aortic and mesenteric artery function of orchidectomized rats. The aim of this study was to investigate whether impaired gonadal function alters the formation of COPs, as well as the potential preventive role of a DHA-supplemented diet on that effect. For this purpose, aortic and mesenteric artery segments obtained from control and orchidectomized rats, fed with a standard or supplemented with DHA, were used. The content of the following COPs: 7α-hydroxycholesterol, 7β-hydroxycholesterol, 7-ketocholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, cholestanetriol and 25-hydroxycholesterol, were analyzed by gas chromatography. The results showed that orchidectomy increased the formation of COPs in arteries from orchidectomized rats, which may participate in the orchidectomy-induced structural and functional vascular alterations already reported. The fact that the DHA-supplemented diet prevented the orchidectomy-induced COPs increase confirms the cardiovascular protective actions of DHA, which could be of special relevance in mesenteric arterial bed, since it importantly controls the systemic vascular resistance.

Ascaroside Profiling of Caenorhabditis elegans Using Gas Chromatography-Electron Ionization Mass Spectrometry

Nematodes such as the model organism Caenorhabditis elegans produce various homologous series of l-ascarylose-derived glycolipids called ascarosides, which include several highly potent signals in intra and interspecies communication as well as cross-kingdom interactions. Given their low concentrations and large number of structurally similar components, mass spectrometric screens based on high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) are commonly employed for ascaroside detection and quantification. Here, we describe a complementary gas chromatography-electron ionization mass spectrometry (GC-EIMS) screen that utilizes an ascarylose-derived K1-fragment ion signal at m/z 130.1 [C₆H₁₄OSi]^+● to highlight known as well as yet unidentified ascaroside components in TMS-derivatized crude nematode exometabolome extracts. GC-EIMS-based ascaroside profiling of wild-type and mutant C. elegans facilitates the analysis of all basic ascarosides using the same ionization technique while providing excellent resolution for the complete homologous series with side chains ranging from 3 to 33 carbons. Combined screening for m/z 130.1 along with side chain-specific J1 [M - 173]⁺ and J2 [M - 291]⁺ fragment ions, as well as additional characteristic marker ions from α-cleavage, enables convenient structure assignment of ca. 200 components from wild-type and peroxisomal β-oxidation mutants including (ω - 1)-linked acyl, enoyl, β-hydroxyacyl, and 2-ketoalkyl ascarosides along with their (ω)-linked or α-methyl isomers and ethanolamide derivatives, as well as 2-hydroxyalkyl ascarosides. Given the widespread availability of GC-MS and its increasing popularity in metabolomics, this method will promote the identification of ascarosides in C. elegans and other nematodes.

Comparison of Two Stationary Phases for the Determination of Phytosterols and Tocopherols in Mango and Its By-Products by GC-QTOF-MS

Two different gas chromatography coupled to quadrupole-time of flight mass spectrometry (GC-QTOF-MS) methodologies were carried out for the analysis of phytosterols and tocopherols in the flesh of three mango cultivars and their by-products (pulp, peel, and seed). To that end, a non-polar column ((5%-phenyl)-methylpolysiloxane (HP-5ms)) and a mid-polar column (crossbond trifluoropropylmethyl polysiloxane (RTX-200MS)) were used. The analysis time for RTX-200MS was much lower than the one obtained with HP-5ms. Furthermore, the optimized method for the RTX-200MS column had a higher sensibility and precision of peak area than the HP-5ms methodology. However, RTX-200MS produced an overlapping between β-sitosterol and Δ⁵-avenasterol. Four phytosterols and two tocopherols were identified in mango samples. As far as we are concerned, this is the first time that phytosterols have been studied in mango peel and that Δ⁵-avenasterol has been reported in mango pulp. α- and γ-tocopherol were determined in peel, and α-tocopherol was the major tocopherol in this fraction (up to 81.2%); however, only α-tocopherol was determined in the pulp and seed. The peel was the fraction with the highest total concentration of phytosterols followed by seed and pulp, and "Sensación" was the cultivar with the highest concentration of total phytosterols in most cases. There were no significant differences between quantification of tocopherols with both columns. However, in most cases, quantification of phytosterols was higher with RTX-200MS than with HP-5ms column.

Identification of a novel component leading to anti-tumor activity besides the major ingredient cordycepin in Cordyceps militaris extract

In accordance with our previous study that was carried out to identify novel anti-tumor ingredients, chromatographic separation in combination with an anti-tumor activity assay was used for analysis of Cordyceps militaris extract in this study. Various modes of chromatography including reversed-phase, cation-exchange and anion-exchange were used to separate components of Cordyceps militaris, which showed various chemical properties. Anti-tumor activity of each fraction was assessed by a Hoechst staining-based apoptosis assay using malignant melanoma MeWo cells. By these repeated approaches through chromatographic segregation and cell biological assay, we finally succeeded in identifying the target substance from a certain fraction that included neutral hydrophilic components using a pre-column and post-column chlorine adduct ionization LC-APCI-MS method. The target substance was a mono-carbohydrate, xylitol, that induced apoptotic cell death in MeWo cells but not in normal human OUMS-24 fibroblasts. This is the first study showing that Cordyceps militaris extract contains a large amount of xylitol. Thus, our results will contribute greatly to uncovering the mysterious multifunctional herbal drug Cordyceps militaris as an anti-tumor agent.

Cytosolic invertase contributes to the supply of substrate for cellulose biosynthesis in developing wood

Carbon for cellulose biosynthesis is derived from sucrose. Cellulose is synthesized from uridine 5'-diphosphoglucose (UDP-glucose), but the enzyme(s) responsible for the initial sucrose cleavage and the source of UDP-glucose for cellulose biosynthesis in developing wood have not been defined. We investigated the role of CYTOSOLIC INVERTASEs (CINs) during wood formation in hybrid aspen (Populus tremula × tremuloides) and characterized transgenic lines with reduced CIN activity during secondary cell wall biosynthesis. Suppression of CIN activity by 38-55% led to a 9-13% reduction in crystalline cellulose. The changes in cellulose were reflected in reduced diameter of acid-insoluble cellulose microfibrils and increased glucose release from wood upon enzymatic digestion of cellulose. Reduced CIN activity decreased the amount of the cellulose biosynthesis precursor UDP-glucose in developing wood, pointing to the likely cause of the cellulose phenotype. The findings suggest that CIN activity has an important role in the cellulose biosynthesis of trees, and indicate that cellulose biosynthesis in wood relies on a quantifiable UDP-glucose pool. The results also introduce a concept of altering cellulose microfibril properties by modifying substrate supply to cellulose biosynthesis.

Use of HPLC- and GC-QTOF to determine hydrophilic and lipophilic phenols in mango fruit (Mangifera indica L.) and its by-products

Mango industry processing generates high quantities of mango by-products such as peels and seeds (35%-60% of the fruit). Indeed, it is known that mango and its by-products contain different families of bioactive compounds that possess several health benefits. Thus, the aim of this study has been the determination of different families of phenolic derivatives (free and bound phenolic compounds and alk(en)ylresorcinols (ARs)) in mango edible part and its by-products (peel, seed and seed husk) from three different cultivars. This is the first study that evaluates the phenolic compounds and ARs in the four fractions of mango of three different cultivars. Special attention has been paid to the determination of anthocyanins and ARs, because these families of compounds had not been studied in depth in mango. In fact, petunidin rutinoside-(p-coumaric acid) gallate was found in mango pulp, peel, seed and seed husk of the three cultivars and, it had never been described in mango before. It is also important to highlight that this is the first time that the identification and quantification of ARs have been performed in mango seed and seed husk; besides, four and five out of eleven alk(en)ylresorcinols detected in peel and pulp, respectively, were identified for the first time in these mango fractions. Furthermore, antioxidant activity was measured by ABTS and FRAP assays. Seed free and bound phenolic extracts showed the highest antioxidant capacity.

Nutritional characteristics and quality of eggs from laying hens fed on a diet supplemented with chestnut tannin extract (Castanea sativa Miller)

The trial was performed with 80 laying hens belonging to two Tuscan autochthonous breeds: 40 birds of the Mugellese (MU) breed and 40 of the White Leghorn (WL) breed. The animals were allotted to 4 groups of individually caged 20 hens each: two groups were fed on a commercial diet and worked as the control groups (MUC and WLC); the other two groups received the same diet, integrated with 2 g of chestnut tannin (CT) extract per kg of diet (MUT and WLT). A sample of 70 eggs were randomly collected and analysed for cholesterol content, fatty acid (FA) profile, weight, thickness of shell and colour of yolk. Physical parameters, including yolk colour, and indices of egg quality were not affected by the treatments. The concentration of unsaturated FAs increased, whereas cholesterol was significantly decreased: -17% in WLT and -9% in MUT. Dietary supplementation with CT extract resulted in a modification of lipid composition, towards a more healthy quality of eggs.

The Galactose-Specific Lectin from the Sponge Chondrilla Nucula Displays Anti-Human Immunodeficiency Virus Activity in vitro via Stimulation of the (2′-5′)Oligoadenylate Metabolism

A new lectin has been isolated from the sponge Chondrilla nucula. The purified CN lectin is a protein composed of four polypeptide chains with a molecular weight (MW) of 15600. The isoelectric point is 4.5 and the amino acid composition is rich in aspartic and glutamic acid. The lectin precipitates erythrocytes from humans (A, B, O) with a titre between 25 and 210. The CN lectin is d-galactose-specific and displays a moderate mitogenic effect on spleen lymphocytes from mice and on CD4-positive human H9 cells. An interesting feature of this lectin is its ability to stimulate the (2′-5′)oligoriboadenylate [(2′-5′)A] metabolic pathway in non-infected and human immunodeficiency virus (HIV-1)-infected H9 cells. Moreover, HIV-1-infected H9 cells show an increase in the time period of HIV-1 release in response to CN lectin treatment. These data suggest that CN lectin causes a retardation of HIV-1 release due to further increase of the elevated intracellular level of (2′-5′)A.

Stability of flavoured phytosterol-enriched drinking yogurts during storage as affected by different packaging materials

BACKGROUND

The aim of this study was to investigate the influence of different packaging materials on storage stability of flavoured phytosterol-enriched drinking yogurts. White vanilla (WV) and blood orange (BO) phytosterol-enriched drinking yogurts conditioned in mono-layer and triple-layer co-extruded plastic bottles were stored at +6 ± 1 °C for 35 days (under alternating 12 h light and 12 h darkness) to simulate shelf-life conditions. Samples were collected at three different storage times and subjected to determination of total sterol content (TSC), peroxide value (PV) and thiobarbituric acid reactive substances (TBARs).

RESULTS

TSC was not significantly affected by packaging material or storage time and met the quantity declared on the label. PV was significantly influenced by yogurt type × packaging material × storage time interaction and TBARs by packaging material × storage time interaction.

CONCLUSION

Between the two packaging materials, the triple-layer plastic mini bottle with black coloured and completely opaque intermediate layer offered the best protection against lipid oxidation. © 2015 Society of Chemical Industry.

GC-MS and LC-MS approaches for determination of tocopherols and tocotrienols in biological and food matrices

Tocopherols and tocotrienols, widely described as vitamin E derivatives, have been proven to take part in a number of important biological functions. Among them, antioxidant properties had been investigated and documented in the literature. Since tocochromanols have revealed their plausible beneficial impact on several pathological processes, such as cancerogenesis or cognitive impairment diseases, there is a growing interest in quantitative determination of these compounds in biological fluids, tissues and plant organs. However, due to vitamin E chemical features, such as lipophilic and non-polar characteristics, quantitative determination of the compounds seems to be problematic. In this paper we present current analytical approaches in tocopherols and tocotrienols determination in biological and food matrices with the use of chromatographic techniques, especially gas chromatography (GC) and high performance liquid chromatography (HPLC) coupled with mass spectrometry. Derivatization techniques applied for GC-MS analysis in the case of tocol derivatives, especially silylation and acylation, are described. Significant attention is paid to ionization process of tocopherols and tocotrienols.

Trehalose Polyphleates Are Produced by a Glycolipid Biosynthetic Pathway Conserved across Phylogenetically Distant Mycobacteria

Mycobacteria synthesize a variety of structurally related glycolipids with major biological functions. Common themes have emerged for the biosynthesis of these glycolipids, including several families of proteins. Genes encoding these proteins are usually clustered on bacterial chromosomal islets dedicated to the synthesis of one glycolipid family. Here, we investigated the function of a cluster of five genes widely distributed across non-tuberculous mycobacteria. Using defined mutant analysis and in-depth structural characterization of glycolipids from wild-type or mutant strains of Mycobacterium smegmatis and Mycobacterium abscessus, we established that they are involved in the formation of trehalose polyphleates (TPP), a family of compounds originally described in Mycobacterium phlei. Comparative genomics and lipid analysis of strains distributed along the mycobacterial phylogenetic tree revealed that TPP is synthesized by a large number of non-tuberculous mycobacteria. This work unravels a novel glycolipid biosynthetic pathway in mycobacteria and extends the spectrum of bacteria that produce TPP.

Determination of lipophilic and hydrophilic bioactive compounds in raw and parboiled rice bran

Rice bran is one of the most important rice by-products and represents a source of bioactive compounds.

A Highly Convergent and Biomimetic Total Synthesis of Portentol

An efficient total synthesis of the unusual polyketide portentol is reported. Three boron aldol reactions were used to assemble the linear carbon chain of the natural product, which contains two challenging anti-anti stereotriads. A biomimetic double cyclization cascade, triggered by an oxidation, then afforded portentol and its known dehydration product, anhydroportentol. The biosynthesis of portentol and the biosynthetic relevance of our key step are discussed.

Thermal oxidation of cholesterol: Preliminary evaluation of 2-methyl-6-heptanone and 3-methylbutanal as volatile oxidation markers

Cholesterol oxidation in food and model systems is usually monitored by evaluating cholesterol oxidation products, but the analysis is time-consuming and expensive. Therefore, the determination of volatile compounds deriving from cholesterol thermoxidation could be valuable to identify other possible oxidation markers. Cholesterol alone and in the presence of a triacylglycerol mixture (tripalmitin, tristearin, and triolein) were thermoxidized at 170°C for 15min. In both model systems, the total volatile compounds increased three times when oxidation time rose from 5 to 15min. The main classes of volatile compounds were aldehydes, ketones, alcohols and hydrocarbons, displaying a similar behavior in both systems. After 5min of oxidation, 2-methyl-6-heptanone was the main volatile compound, followed by 3-methylpentane, 2,3-dimethyl-1-pentene and 3-methylbutanal. To verify if 2-methyl-6-heptanone could be used as volatile marker of cholesterol oxidation, data were compared with the total cholesterol oxidation products content of each system. A significant correlation between total cholesterol oxidation products content and 2-methyl-6-heptanone amount was found when cholesterol was oxidized alone (r(2)=0.994) and in presence of triacylglycerols (r(2)=0.998). When egg yolk was thermoxidized at 80°C for 6h, 3-methylbutanal was the volatile compound that better explained the oxidative trend in this food system, showing a significant correlation with cholesterol oxidation rate (r=0.91). In conclusion, 2-methyl-6-heptanone and 3-methylbutanal could represent an easy and cheaper strategy for monitoring cholesterol oxidation in model systems and food samples, respectively; however, a deeper investigation on the amount and type of volatile compounds generated from cholesterol oxidation according to the food matrix, should be carried out.

Studies into the phenolic patterns of different tissues of pineapple (Ananas comosus [L.] Merr.) infructescence by HPLC-DAD-ESI-MS (n) and GC-MS analysis

In a comprehensive study, more than 60 phenolic compounds were detected in methanolic extracts from different tissues of pineapple infructescence by high-performance liquid chromatography with diode array detection and electrospray ionisation multiple-stage mass spectrometry (HPLC-DAD-ESI-MS (n) ) as well as by gas chromatography-mass spectrometry (GC-MS). The analytical workflow combining both methods revealed numerous compounds assigned for the first time as pineapple constituents by their mass fragmentations. Pineapple crown tissue was characterised by depsides of p-coumaric and ferulic acid. In contrast, major phenolic compounds in pineapple pulp extracts were assigned to diverse S-p-coumaryl, S-coniferyl and S-sinapyl derivatives of glutathione, N-L-γ-glutamyl-L-cysteine and L-cysteine, which were also identified in the peel. The latter was additionally characterised by elevated concentrations of p-coumaric, ferulic and caffeic acid depsides and glycerides, respectively. Two peel-specific cyanidin hexosides were found. Elevated concentrations of isomeric N,N'-diferuloylspermidines may be a useful tool for the detection of fraudulent peel usage for pineapple juice production. Mass fragmentation pathways of characteristic pineapple constituents are proposed, and their putative biological functions are discussed.

Effect of Microwave Heating on Phytosterol Oxidation

The oxidative stability of phytosterols during microwave heating was evaluated. Two different model systems (a solid film made with a phytosterol mixture (PSF) and a liquid mixture of phytosterols and triolein (1:100, PS + TAG (triacylglycerol))) were heated for 1.5, 3, 6, 12, 20, and 30 min at 1000 W. PS degraded faster when they were microwaved alone than in the presence of TAG, following a first-order kinetic model. Up to 6 min, no phytosterol oxidation products (POPs) were generated in both systems. At 12 min of heating, the POP content reached a higher level in PSF (90.96 μg/mg of phytosterols) than in PS + TAG (22.66 μg/mg of phytosterols), but after 30 min of treatment, the opposite trend was observed. 7-Keto derivates were the most abundant POPs in both systems. The extent of phytosterol degradation depends on both the heating time and the surrounding medium, which can impact the quality and safety of the food product destined to microwave heating/cooking.

Glucose: Detection and analysis

Glucose is an aldosic monosaccharide that is centrally entrenched in the processes of photosynthesis and respiration, serving as an energy reserve and metabolic fuel in most organisms. As both a monomer and as part of more complex structures such as polysaccharides and glucosides, glucose also plays a major role in modern food products, particularly where flavor and or structure are concerned. Over the years, many diverse methods for detecting and quantifying glucose have been developed; this review presents an overview of the most widely employed and historically significant, including copper iodometry, HPLC, GC, CZE, and enzyme based systems such as glucose meters. The relative strengths and limitations of each method are evaluated, and examples of their recent application in the realm of food chemistry are discussed.

CaO as drop-in colloidal catalysts for the synthesis of higher polyglycerols

Glycerol is an attractive renewable building block for the synthesis of polyglycerols, which find application in the cosmetic and pharmaceutical industries. The selective etherification of glycerol to higher oligomers was studied in the presence of CaO colloids and the data are compared with those obtained from NaOH and CaO. The materials were prepared by dispersing CaO, CaCO3 , or Ca(OH)2 onto a carbon nanofiber (CNF) support. Colloidal nanoparticles were subsequently dispensed from the CNF into the reaction mixture to give CaO colloids that have a higher activity than equimolar amounts of bulk CaO and NaOH. Optimization of the reaction conditions allowed us to obtain a product with Gardner color number <2, containing no acrolein and minimal cyclic byproducts. The differences in the CaO colloids originating from CNF and bulk CaO were probed using light scattering and conductivity measurements. The results confirmed that the higher activity of the colloids originating from CaO/CNF was due to their more rapid formation and smaller size compared with colloids from bulk CaO. We thus have developed a practical method for the synthesis of polyglycerols containing low amounts of Ca.

Chemoselective per-O-trimethylsilylation and homogeneous N-functionalisation of amino sugars

HomogeneousN-functionalisation of amino sugars can be achievedviaefficient CH₃CN-promoted hexamethyldisilazane per-O-trimethylsilylation.