Analysis of Cuticular Lipids of the Pharaoh Ant (Monomorium pharaonis) and Their Selective Adsorption on Insecticidal Zeolite Powders.

The pharaoh ant is a notorious and hard to eradicate pest, which poses a threat in hospitals, spreading pathogens and contaminating sterile equipment. When applied on ants, zeolites adsorb part of their epicuticular wax layer. The ants are then vulnerable to desiccation, since this layer regulates water exchange. We analyzed the chemical composition of this wax layer using GC-MS (Gas Chromatography-Mass Spectrometry). A hexane wash of M. pharaonis foragers resulted in the identification of 53 components, four of which were not previously defined in Monomorium species. Selective adsorption of specific compounds on zeolites assisted in the identification of compounds which could not be separated on the GC column and allowed for the identification of three additional compounds. Zeolites show different affinities for the wax compounds depending on pore structure and chemical composition. Selective adsorption of alkanes on zeolites is also investigated in the fields of refinery processes and catalysis. Pore mouth and key lock adsorption mechanisms and selectivity according to molecular weight and branching, investigated in these fields, are also involved in adsorption processes of epicuticular waxes. The insecticidal activity of a zeolite is related to adsorption selectivity rather than capacity. One of the best adsorbing zeolites showed limited insecticidal activity and can be considered as a non-lethal alternative for epicuticular wax sampling.

Impact of casein and egg white proteins on the structure of wheat gluten-based protein-rich food.

BACKGROUND: There is a growing interest in texturally and nutritionally satisfying vegetable alternatives to meat. Wheat gluten proteins have unique functional properties but a poor nutritional value in comparison to animal proteins. This study investigated the potential of egg white and bovine milk casein with well-balanced amino acid composition to increase the quality of wheat gluten-based protein-rich foods. RESULTS: Heating a wheat gluten (51.4 g)-water (100.0 mL) blend for 120 min at 100 °C increased its firmness less than heating a wheat gluten (33.0 g)-freeze-dried egg white (16.8 g)-water (100.0 mL) blend. In contrast, the addition of casein to the gluten-water blend negatively impacted firmness after heating. Firmness was correlated with loss of protein extractability in sodium dodecyl sulfate containing medium during heating, which was higher with egg white than with casein. Even more, heat-induced polymerization of the gluten-water blend with egg white but not with casein was greater than expected from the losses in extractability of gluten and egg white on their own. CONCLUSION: Structure formation was favored by mixing gluten with egg white but not with casein. These observations were linked to the intrinsic polymerization behavior of egg white and casein, but also to their interaction with gluten. Thus not all nutritionally suitable proteins can be used for enrichment of gluten-based protein-rich foods.

Cross-linking of wheat gluten proteins during production of hard pretzels.

The impact of the hot alkaline dip, prior to pretzel-baking, on the types and levels of cross-links between wheat proteins was studied. Protein extractability of pretzel dough in sodium dodecyl sulfate containing buffer decreased during alkaline dipping [45 s, 1.0% (w/v) NaOH, 90°C], and even more during baking (3 min at 250°C) and drying (10 min at 135°C). Reducing agent increased the extractability partly, indicating that both reducible (disulfide, SS) and non-reducible (non-SS) protein cross-links had been formed. The decrease in cystine levels suggested ß-elimination of cystine releasing Cys and dehydroalanine (DHA). Subsequent reaction of DHA with Lys and Cys, induced the unusual and potentially cross-linking amino acids lysinoalanine (LAL) and lanthionine (LAN), respectively, in alkaline dipped dough (7 µmol LAN/g protein) and in the end product (9 µmol LAL and 50 µmol LAN/g protein). The baking/drying step increased sample redness, decreased Lys levels more than expected based on LAL formation (57 µmol/g protein), and induced a loss of reducing sugars (99 µmol/g protein), which suggested the potential contribution of Maillard-derived cross-links to the observed extractability loss. However, levels of Maillard products which possibly cross-link proteins, are small compared to DHA-derived cross-links. Higher dipping temperatures, longer dipping times, and higher NaOH concentrations increased protein extractability losses and redness, as well as LAL and LAN levels in the end product. No indications for Maillard-derived cross-links or LAL in pretzel dough immediately after dipping were found, even when severe dipping conditions were used.

Redox agents and N-ethylmaleimide affect the extractability of gluten proteins during fresh pasta processing.

The gluten protein network is of great importance for pasta cooking quality. Redox agents were used as a tool to impact the protein network formation during laboratory scale fresh pasta making (mixing and sheet rolling) and cooking. SE- and RP-HPLC data showed that disulphide bonds are formed in the pre-existing gluten protein network during cooking of fresh pasta and that, in the process, glutenin polymerisation occurs faster than gliadin-glutenin copolymerisation. The thiol blocking agent N-ethylmaleimide (245ppm, expressed on semolina, dry basis) and, to a lesser extent, the oxidising agent potassium iodate (70ppm), hindered glutenin polymerisation and gliadin-glutenin copolymerisation during cooking. However, the introduction of reactive thiol groups, by addition of the reducing agent glutathione (100ppm), resulted in faster gliadin-glutenin copolymerisation during cooking.

Molecular basis of processing wheat gluten toward biobased materials.

The unique properties of the wheat grain reside primarily in the gluten-forming storage proteins of its endosperm. Wheat gluten's structural and functional properties have led to an expanding diversity of applications in food products. However, its viscoelastic properties and low water solubility also are very interesting features for nonfood applications. Moreover, gluten is annually renewable and perfectly biodegradable. In the processing and setting of gluten containing products, temperature plays a very important role. In this review, the structure and reactivity of gluten are discussed and the importance of sulfhydryl (SH) and disulfide (SS) groups is demonstrated. Wheat gluten aggregation upon thermosetting proceeds through direct covalent cross-linking in and between its protein groups, glutenin and gliadin. Predominant reactions include SH oxidation and SH/SS interchange reactions leading to the formation of SS cross-links. Additionally, thermal treatment of gluten can result in the formation of other than SS covalent bonds. We here review two main technological approaches to make gluten-based materials: wet processes resulting in thin films and dry processes, such as extrusion or compression molding, exploiting the thermoplastic properties of proteins under low moisture conditions and potentially resulting in very useful materials. Gluten bioplastics can also be reinforced with natural fibers, resulting in biocomposites. Although a lot of progress has been made the past decade, the current gluten materials are still outperformed by their synthetic polymer counterparts.

A sustainable wood biorefinery for low-carbon footprint chemicals production.

The profitability and sustainability of future biorefineries are dependent on efficient feedstock use. Therefore, it is essential to valorize lignin when using wood. We have developed an integrated biorefinery that converts 78 weight % (wt %) of birch into xylochemicals. Reductive catalytic fractionation of the wood produces a carbohydrate pulp amenable to bioethanol production and a lignin oil. After extraction of the lignin oil, the crude, unseparated mixture of phenolic monomers is catalytically funneled into 20 wt % of phenol and 9 wt % of propylene (on the basis of lignin weight) by gas-phase hydroprocessing and dealkylation; the residual phenolic oligomers (30 wt %) are used in printing ink as replacements for controversial para-nonylphenol. A techno-economic analysis predicts an economically competitive production process, and a life-cycle assessment estimates a lower carbon dioxide footprint relative to that of fossil-based production.

Wheat Gluten Amino Acid Analysis by High-Performance Anion-Exchange Chromatography with Integrated Pulsed Amperometric Detection.

The present chapter describes an accurate and user-friendly method for determining amino acid composition of wheat gluten proteins and their gliadin and glutenin fractions. The method consists of hydrolysis of the peptide bonds in 6.0 M hydrochloric acid (HCl) solution at 110 °C for 24 h, followed by evaporation of the acid and separation of the free amino acids by high-performance anion-exchange chromatography with integrated pulsed amperometric detection (HPAEC-IPAD). In contrast to conventional methods, the analysis requires neither pre- or post-column derivatization nor a time-consuming oxidation or derivatization step prior to hydrolysis. Correction factors account for incomplete release of Val and Ile even after hydrolysis for 24 h and for losses of Ser during evaporation. Gradient conditions including an extra eluent allow multiple sequential sample analyses without risk of Glu accumulation on the anion-exchange column which otherwise would result from high Gln levels in gluten proteins.

Material properties determining the insecticidal activity of highly divided porous materials on the pharaoh ant (Monomorium pharaonis).

BACKGROUND: Historically, inert insecticidal powders such as diatomaceous earth were researched for pest management applications, and it was revealed that these types of powders killed insects by desiccation. However, data on the critical material properties that affect their efficacy are sparse. The present study investigated the insecticidal effect of powdered materials on the pharaoh ant, a notorious domestic pest. RESULTS: The insecticidal activity of 24 porous materials was tested. Eight of these materials performed better than the benchmark, diatomaceous earth. Zeolite Y and carbon black II performed best, inducing 50% mortality within 40 and 55 minutes, respectively. Statistical analysis of seven material properties revealed that macroporous surface area and Brunauer-Emmett-Teller (BET) specific surface area were most predictive of insecticidal activity. For zeolites and ordered mesoporous silica materials, the most important parameters were, respectively, BET and large mesopore surface area. Finally, gas chromatography-mass spectrometry (GC-MS) analysis confirmed the adsorption of epicuticular hydrocarbons onto the zeolite powders. CONCLUSION: This study shows clear potential for the use of environmentally friendly, inert porous materials as insecticides against the pharaoh ant and identified the key material properties influencing insecticidal activity. The GC-MS data support the hypothesis that the mortality was caused by the removal of the protective epicuticular hydrocarbons. © 2017 Society of Chemical Industry.

Impact of redox agents on the extractability of gluten proteins during bread making.

The gluten proteins gliadin and glutenin are important for dough and bread characteristics. In the present work, redox agents were used to impact gluten properties and to study gliadin-glutenin interactions in bread making. In control bread making, mixing increased the extractability of glutenin. The level of SDS-extractable glutenin decreased during fermentation and then further in the oven. The levels of extractable alpha- and gamma-gliadin also decreased during bread baking due to gliadin-glutenin polymerization. Neither oxidizing nor reducing agents had an impact on glutenin extractabilities after mixing. The redox additives did not affect omega-gliadin extractabilities during bread making due to their lack of cysteine residues. Potassium iodate (0.82-2.47 micromol/g of protein) and potassium bromate (1.07-3.17 micromol/g of protein) increased both alpha- and gamma-gliadin extractabilities during baking. Increasing concentrations of glutathione (1.15-3.45 micromol/g of protein) decreased levels of extractable alpha- and gamma-gliadins during baking. The work not only demonstrated that, during baking, glutenin and gliadin polymerize through heat-induced sulfhydryl-disulfide exchange reactions, but also demonstrated for the first time that oxidizing agents, besides their effect on dough rheology and hence bread volume, hinder gliadin-glutenin linking during baking, while glutathione increases the degree of covalent gliadin to glutenin linking.

Adsorption and Separation of Aromatic Amino Acids from Aqueous Solutions Using Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are investigated for the adsorption of aromatic amino acids l-phenylalanine (l-Phe), l-tryptophan (l-Trp), and l-tyrosine (l-Tyr) from aqueous solutions. After screening a range of water-stable MOFs, the hydrophobic Zr-MOF MIL-140C emerged as the best performing material, exhibiting uptakes of 15 wt % for l-Trp and 20 wt % for l-Phe. These uptakes are 5-10 wt % higher than those of large-pore zeolites Beta and Y. Both single-compound and competitive adsorption isotherms for l-Phe and l-Trp were experimentally obtained at the natural pH of these amino acid mixtures (pH 6.5-7) without additional pH modification. We find that the hydrophobic nature of MIL-140C and the capacity of l-Trp to form hydrogen bonds favor the uptake of l-Trp with its larger indole moiety compared to the smaller phenyl side group of l-Phe. On the basis of literature and vibrational analysis, observations of hydrogen-bonded l-Trp within the MIL-140C framework are evidenced by red- and blue-shifted -NH vibrations (3400 cm-1) in Fourier transform infrared spectroscopy, which were attributed to types N-Hl-Trp···πMIL-140C and N-Hl-Trp···OMIL-140C, respectively. MIL-140C is shown to be recycled at least three times for both aromatic amino acids without any loss of adsorption capacity, separation performance, or crystallinity. Desorption of aromatic amino acids proceeds easily in aqueous ethanol. Substantial coadsorption of negatively charged amino acids l-glutamate and l-aspartate (l-Glu and l-Asp) was observed from a model solution for wheat straw protein hydrolysate at pH 4.3. On the basis of these results, we conclude that MIL-140C is an interesting material for the recovery of essential aromatic amino acids l-Tyr, l-Phe, and l-Trp and of l-Glu and l-Asp from waste protein hydrolysates.

Redox agents and N-ethylmaleimide affect protein polymerization during laboratory scale dry pasta production and cooking.

Durum wheat (Triticum durum Desf.) semolina gluten proteins consist of monomeric gliadin and polymeric glutenin and determine the quality of pasta products made therefrom. During pasta drying, glutenin starts polymerizing already below 60 °C (65% relative humidity (RH)), whereas gliadin only is incorporated in the protein network at temperatures exceeding 68 °C (68% RH) through thiol (SH)/disulfide (SS) exchange reactions. Removal of free SH groups in glutenin by adding 2.3 µmol KBrO3 or KIO3 per g dry matter semolina protein (g protein) or 13.8 µmol N-ethylmaleimide/g protein reduces gliadin-glutenin cross-linking during pasta drying and/or cooking and yields cooked pasta of high quality. Introducing free SH groups by adding 13.8 µmol glutathione/g protein increases gliadin-glutenin cross-linking during pasta processing, resulting in cooked pasta of lower quality. We hypothesize that too much gliadin incorporation in the glutenin network during pasta processing tightens the protein network and results in lower cooking quality.

Formation and reshuffling of disulfide bonds in bovine serum albumin demonstrated using tandem mass spectrometry with collision-induced and electron-transfer dissociation.

Thermolysin hydrolyzates of freshly isolated, extensively stored (6 years, 6 °C, dry) and heated (60 min, 90 °C, in excess water) bovine serum albumin (BSA) samples were analyzed with liquid chromatography (LC) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) using alternating electron-transfer dissociation (ETD) and collision-induced dissociation (CID). The positions of disulfide bonds and free thiol groups in the different samples were compared to those deduced from the crystal structure of native BSA. Results revealed non-enzymatic posttranslational modifications of cysteine during isolation, extensive dry storage, and heating. Heat-induced extractability loss of BSA was linked to the impact of protein unfolding on the involvement of specific cysteine residues in intermolecular and intramolecular thiol-disulfide interchange and thiol oxidation reactions. The here developed approach holds promise for exploring disulfide bond formation and reshuffling in various proteins under conditions relevant for chemical, biochemical, pharmaceutical and food processing.

Ruthenium-catalyzed aerobic oxidative decarboxylation of amino acids: a green, zero-waste route to biobased nitriles.

Oxidative decarboxylation of amino acids into nitriles was performed using molecular oxygen as terminal oxidant and a heterogeneous ruthenium hydroxide-based catalyst. A range of amino acids was oxidized in very good yield, using water as the solvent.

Bio-based nitriles from the heterogeneously catalyzed oxidative decarboxylation of amino acids.

The oxidative decarboxylation of amino acids to nitriles was achieved in aqueous solution by in situ halide oxidation using catalytic amounts of tungstate exchanged on a [Ni,Al] layered double hydroxide (LDH), NH4 Br, and H2 O2 as the terminal oxidant. Both halide oxidation and oxidative decarboxylation were facilitated by proximity effects between the reactants and the LDH catalyst. A wide range of amino acids was converted with high yields, often >90 %. The nitrile selectivity was excellent, and the system is compatible with amide, alcohol, and in particular carboxylic acid, amine, and guanidine functional groups after appropriate neutralization. This heterogeneous catalytic system was applied successfully to convert a protein-rich byproduct from the starch industry into useful bio-based N-containing chemicals.

Storage of parbaked bread affects shelf life of fully baked end product: a ¹H NMR study.

Full baking of earlier partially baked (parbaked) bread can supply fresh bread to the consumer at any time of the day. When parbaked bread loaves were stored at -25, 4 or 23°C, the extent of crumb to crust moisture migration and amylopectin retrogradation differed with storage temperature, and the firming rate was evidently lowest during frozen storage. The extent of crumb to crust moisture migration during parbaked bread storage largely determined the mass of the fresh finished bread, and its crumb and crust moisture contents. Initial NMR proton mobility, initial resilience, the extent of amylopectin retrogradation and changes in firmness and resilience during storage of fully baked bread were affected by its crumb moisture content. The lowest firming rate was observed for finished bread resulting from parbaked bread stored at -25°C, while the highest firming rate was observed for finished bread from parbaked bread stored at 23°C.

Identification of intact high molecular weight glutenin subunits from the wheat proteome using combined liquid chromatography-electrospray ionization mass spectrometry.

The present paper describes a method for the identification of intact high molecular weight glutenin subunits (HMW-GS), the quality determining proteins from the wheat storage proteome. The method includes isolation of HMW-GS from wheat flour, further separation of HMW-GS by reversed-phase high-performance liquid chromatography (RP-HPLC), and their subsequent molecular identification with electrospray ionization mass spectrometry using a quadrupole-time-of-flight mass analyzer. For HMW-GS isolation, wheat proteins were reduced and extracted from flour with 50% 1-propanol containing 1% dithiothreitol. HMW-GS were then selectively precipitated from the protein mixture by adjusting the 1-propanol concentration to 60%. The composition of the precipitated proteins was first evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Coomassie staining and RP-HPLC with ultraviolet detection. Besides HMW-GS (≥65%), the isolated proteins mainly contained ω5-gliadins. Secondly, the isolated protein fraction was analyzed by liquid chromatography-mass spectrometry. Optimal chromatographic separation of HMW-GS from the other proteins in the isolated fraction was obtained when the mobile phase contained 0.1% trifluoroacetic acid as ion-pairing agent. Individual HMW-GS were then identified by determining their molecular masses from the high-resolution mass spectra and comparing these with theoretical masses calculated from amino acid sequences. Using formic acid instead of trifluoroacetic acid in the mobile phase increased protein peak intensities in the base peak mass chromatogram. This allowed the detection of even traces of other wheat proteins than HMW-GS in the isolated fraction, but the chromatographic separation was inferior with a major overlap between the elution ranges of HMW-GS and ω-gliadins. Overall, the described method allows a rapid assessment of wheat quality through the direct determination of the HMW-GS composition and offers a basis for further top-down proteomics of individual HMW-GS and the entire wheat glutenin fraction.

Impact of amylases on biopolymer dynamics during storage of straight-dough wheat bread.

When Bacillus stearothermophilus α-amylase (BStA), Pseudomonas saccharophila α-amylase (PSA), or Bacillus subtilis α-amylase (BSuA) was added to a bread recipe to impact bread firming, amylose crystal formation was facilitated, leading to lower initial crumb resilience. Bread loaves that best retained their quality were those obtained when BStA was used. The enzyme hindered formation of an extended starch network, resulting in less water immobilization and smaller changes in crumb firmness and resilience. BSuA led to extensive degradation of the starch network during bread storage with release of immobilized water, eventually resulting in partial structure collapse and poor crumb resilience. The most important effect of PSA was an increased bread volume, resulting in smaller changes in crumb firmness and resilience. A negative linear relation was found between NMR proton mobilities of water and biopolymers in the crumb and crumb firmness. The slope of that relation gave an indication of the strength of the starch network.

The impact of baking time and bread storage temperature on bread crumb properties.

Two baking times (9 and 24 min) and storage temperatures (4 and 25 °C) were used to explore the impact of heat exposure during bread baking and subsequent storage on amylopectin retrogradation, water mobility, and bread crumb firming. Shorter baking resulted in less retrogradation, a less extended starch network and smaller changes in crumb firmness and elasticity. A lower storage temperature resulted in faster retrogradation, a more rigid starch network with more water inclusion and larger changes in crumb firmness and elasticity. Crumb to crust moisture migration was lower for breads baked shorter and stored at lower temperature, resulting in better plasticized biopolymer networks in crumb. Network stiffening, therefore, contributed less to crumb firmness. A negative relation was found between proton mobilities of water and biopolymers in the crumb gel network and crumb firmness. The slope of this linear function was indicative for the strength of the starch network.

Biopolymer interactions, water dynamics, and bread crumb firming.

To establish the relationship between biopolymer interactions, water dynamics, and crumb texture evolution in time, proton mobilities in starch and gluten model systems and bread were investigated with NMR relaxometry. Amylopectin recrystallization was observed as an increased amount of fast-relaxing protons, while network strengthening and changes in water levels were noted as a reduced mobility and amount, respectively, of slowly relaxing protons. Amylopectin recrystallization strengthened the starch network with concomitant inclusion of water and increased crumb firmness, especially at the beginning of storage. The inclusion of water and the thermodynamic immiscibility of starch and gluten resulted in local gluten dehydration during bread storage. Moisture migration from crumb to crust further reduced the level of plasticizing water of the biopolymer networks and contributed to crumb firmness at longer storage times. Finally, we noted a negative relationship between the mobility of slowly relaxing protons of crumb polymers and crumb firmness.

Importance of thiol-functionalized molecules for the structure and properties of compression-molded glassy wheat gluten bioplastics.

High-temperature compression molding of wheat gluten at low water levels yields a rigid plastic-like material. We performed a systematic study to determine the effect of additives with multiple thiol (SH) groups on gluten network formation during processing and investigate the impact of the resulting gluten network on the mechanical properties of the glassy end product. To this end, a fraction of the hydroxyl groups of different polyols was converted into SH functionalities by esterifying with 3-mercaptopropionic acid (MPA). The monofunctional additive MPA was evaluated as well. During low-temperature mixing SH-containing additives decreased the gluten molecular weight, whereas protein cross-linking occurred during high-temperature compression molding. The extent of both processes depended on the molecular architecture of the additives and their concentration. After molding, the material strength and failure strain increased without affecting the modulus, provided the additive concentration was low. The strength decreased again at too high concentrations for polyols with low SH functionalization. Attributing these effects solely to the interplay of plasticization and the SH-facilitated introduction of cross-links is inadequate, since an improvement in both strength and failure strain was also observed in the presence of high levels of MPA. It is hypothesized that, regardless of the molecular structure of the additive, the presence of SH-containing groups induces conformational changes which contribute to the mechanical properties of glassy gluten materials.