An Investigation on the Reduced Ability of IF-MoS2 Nanoparticles to Reduce Friction and Wear in the Presence of Dispersants

Inorganic fullerene-like molybdenum disulfide (IF-MoS₂) nanoparticles are known to exhibit great friction and wear-reducing abilities in severe boundary lubrication regimes, when added to a base oil alone. Their use in fully formulated lubricants was investigated in this study, and the tribological benefits attributed to the IF-MoS₂ nanoparticles were found to be lost in the presence of dispersants. Various experimental techniques were used on three reference oils (base oil containing only IF-MoS_2, only dispersants and both IF-MoS₂ and dispersants) in order to understand the effect of succinimide-based dispersants on the three phases needed for effective nanoparticle-based lubrication, namely (1) the passing of the nanoparticles through the contact (2) the exfoliation of the IF-MoS₂ inside the contact and (3) the adhesion of the released MoS₂ platelets on the friction surfaces. The dispersants were shown to improve the dispersion of the nanoparticles in the oil by reducing their agglomeration, but prevented the adhesion of a low-friction MoS₂ tribofilm on the steel surfaces. In-situ contact visualization revealed that the well-dispersed nanoparticles passed through the contact and exfoliated nanoparticles were observed after tribological testing. These results imply that nanoparticle dispersion itself does not seem to be an issue concerning nanoparticle effectiveness, even though the reduced agglomerate size and inertia may have affected nanoparticle flow near the contact, as well as entrapment and exfoliation conditions inside the contact. The use of succinimide-based dispersants may, however, have affected the tribochemistry of the contact, by an excessive adsorption on the steel surfaces and/or by encapsulating the released MoS₂ platelets, preventing tribofilm adhesion. A balance was finally found between nanoparticle dispersion and friction reduction, but for very low dispersant concentrations and after a running-in period. The role of succinimide-based dispersants and their effect on nanoparticle lubrication were discussed in the light of these results.     

Glucosinolates in isaño (Tropaeolum tuberosum) tubers: qualitative and quantitative content and changes after maturity

Six varieties of isaño (Tropaeolum tuberosum), an Andean edible tuber, were analysed. The aim was to characterise qualitatively and quantitatively their content of glucosinolates and to determine concentration changes of these compounds upon delayed harvest. Additionally, exploratory assays were carried out on the effect of postharvest cold storage of the tubers as well as of a drying process imposed on blanched tuber slices. Only one glucosinolate (p‐methoxybenzyl glucosinolate) was found in the six domestic varieties analysed. Its concentration varied between 36.5 and 90.0 µmol g^?1 dry matter. This range is relatively high when compared with other edible glucosinolate‐containing vegetables. ‘Dark’ coloured tuber varieties showed higher levels than ‘light’ coloured tuber varieties at normal harvest time. Of the two varieties on which the effect of delayed harvest was studied, one showed increasing and then decreasing changes until 44 days after maturity, while the other did not show any significant change with time. Postharvest cold stored samples showed similar changes to tubers kept in soil, and glucosinolate levels in dried blanched tubers did not differ significantly from those in fresh samples. Taken together, the data indicate that the glucosinolate content of isaño is highly dependent on both the variety and the time of harvest. These parameters should be taken into account when considering isaño as a promising food source with medicinal properties for humans and animals, but also with possible adverse biological effects, all related to the presence of glucosinolates. Copyright © 2004 Society of Chemical Industry     

In vitro gastrointestinal digestion of liquid and semi-liquid dairy matrixes

Protein digestion in two liquid dairy matrixes with different heat treatments (pasteurized and sterilized milks) and in one semi-liquid dairy matrix (stirred-yogurt) was investigated using an in vitro gastrointestinal digestion model. After buccal digestion, significantly lower amount of soluble proteins were measured in yogurt than in both milks. This difference between dairy matrixes decreased during gastric digestion and disappeared at the end of the duodenal digestion upon the proteolytic action of pepsin and pancreatin. Electrophoresis pattern of digested mixtures showed that casein digestion began at the gastric phase and was slower for pasteurized milk than sterilized milk and yogurt. At the end of duodenal digestion, no more intact caseins were present in all the dairy matrixes while faint bands of whey proteins were still visible for pasteurized milk and yogurt. The release of free amino acids during the duodenal phase varied according to their nature (acid, basic, neutral or hydrophobic) and seems to be governed by the specificity of the enzymes. These results suggest that the severity of milk's heat treatment influences the kinetics of protein digestion, mainly during the gastric phase, and that the impact of processing has to be considered to study protein digestion in dairy products.     

Spectroscopic study of copper(II)--wheat straw cell wall residue surface complexes

The sorption of copper(II) by wheat straw cell wall residue (CWR) was studied and revealed a relatively stable surface complexation on the acid sites of the substrate (carboxylic and phenolic moieties). The copper binding capacity at pH = 5.75 and ionic strength of 0.1 M was evaluated at 63 micromol x g(-1) CWR. The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior for the system at different pH values. Batch experiments have been achieved in the presence of calcium in order to mimic the calcareous soil of the Champagne region. A competitive effect on copper complexation has been shown, which is presumably due to the calcium ability to form outer-sphere complexes far less stable than copper(II) ones. Electron spin resonance and X-ray absorption spectroscopy were combined to obtain information on the geometry and structure of Cu bound to CWR. At least two different binding sites for Cu2+ were found to take place in CWR. From ESR parameters, we deduced that copper(II) ions, when complexed with CWR, are coordinated in a square-planar arrangement with four oxygen-containing groups. EXAFS and XANES experiments revealed that Cu(II) is surrounded by four oxygen atoms, with an average Cu-O equatorial distance equal to 1.94 A.     

Size distribution of fat globules in human colostrum, breast milk, and infant formula

Only a few results are available on the size of human milk fat globules (MFG), despite its significance regarding fat digestion in the infant, and no data are available at <24 h postpartum (PP). We measured the MFG size distribution in colostrum and transitional human milk in comparison with fat globules of mature milk and infant formula. Colostrum and transitional milk samples from 18 mothers were collected regularly during 4 d PP and compared with mature milk samples of 17 different mothers and 4 infant formulas. The size distribution was measured by laser light scattering. For further characterization, the ζ-potential of some mature MFG was measured by laser Doppler electrophoresis. The MFG diameter decreased sigmoidally in the first days. At <12 h PP, the mode diameter was 8.9 ± 1.0 μm vs 2.8 ±0.3 μm at 96 h PP. Thus, the surface area of MFG increased from 1.1 ±0.3 to 5.4 ±0.7 m²/g between colostrum and transitional milk. In mature milk, the MFG diameter was 4 μm on average and increased with advancing lactation, whereas the droplets in infant formula measured 0.4 μm. The ζ potential of mature MFG was −7.8 ± 0.1 mV. The fat globules are larger in early colostrum than in transitional and mature human milk and in contrast with the small-sized fat droplets in infant formula. Human MFG also have a low negative surface charge compared with bovine globules. These structural differences can be of nutritional significance for the infant.     

14C labelling of lignins of normal and bm3 maizes for fermentation studies

[U-¹⁴C] phenylalanine (phe*) and [O¹⁴CH₃] sinapic acid (sin*) were infused into the cut ends of normal and bm3 maizes (anthesis stage) under or above the last node or at mid-internode, with or without the leaf, in light or in darkness. Radioactivity was measured in the organs, and in phenolic constituents of the cell wall and saponified residues of the bases and tops of the apical inter-node. In both maize genotype labelled under the node the radioactivity was distributed more evenly in the organs with sin* than with phe*. Infusion above the node and at mid-internode greatly increased radioactivity in the bases and tops, respectively. Removal of the leaf only slightly increased the radioactivity, mainly in the bases, and no clear-cut effect of darkness was observed. Phe* labelled the phenolic acids and the three lignin units, but the syringyl units of bm3 maize were only slightly labelled. Sin* specifically labelled the syringyl units, which represented the least condensed fraction of lignins. Both the native and labelled lignins were highly alkali soluble. There were differences in lignin biogenesis between the bases and tops, and between normal and bm3 maizes. The newly formed lignins were slightly different from the native lignins but had similar types of heterogeneity, with variations in the internode and between genotypes similar to those in native lignins. Provided due allowance is made for the distinguishing characteristics of newly formed lignins, the [¹⁴C-lignin] cell walls, which are strongly labelled on complementary structures, seem suitable model substrates for fermentation studies.     

Fruit load or fruit position alters response to temperature and subsequently cherry tomato quality

Changes in fruit–source ratio during the growth and maturation of cherry tomato fruits were studied in combination with increased fruit temperature. Six treatments were compared: the presence or absence of local heating combined with different fruit origins (7P, fruit from trusses pruned to seven flowers; 14P, proximal fruits; 14D, distal fruits from trusses pruned to 14 flowers). 7P were less sensitive to heating whereas 14P and 14D showed greater reduction in water and dry matter (DM) content. Distal fruits had the lowest structural DM (sDM), which could be due to a lower fruit cell number. Heating further decreased the sDM, so that fruit sink size was the lowest for distal fruits subjected to heating. Under low competition (7P), heating had a beneficial effect on sugar and lycopene content, whereas acids, β‐carotene and vitamin C content were reduced. Under high competition (14P, 14D), heating increased the ratio sDM–DM. This was mainly due to the reduced content of sugars and acids, but also to the reduced accumulation of secondary metabolites such as vitamin C, β‐carotene and lycopene. This study underlines the interactions between fruit temperature and the fruit–source ratio and the consequences for fruit composition and nutritional quality. Copyright © 2005 Society of Chemical Industry     

Nutritive value of rapeseed meal: Effects of individual glucosinolates

In the first of a series of studies on the nutritional value of rapeseed meal, rats were fed diets containing six individual glucosinolates over a period of 29 days. The diets included progoitrin and gluconapin both of which are major components of high glucosinolate rapeseed cultivars. No reduction of feed intake or growth rate was noted and thyroid weights were significantly affected only by the progoitrin diet, which also produced small increases in the weights of the livers and kidneys. There was no depression of plasma thyroid hormone levels.     

Delta13C values of grasses as a novel indicator of pollution by fossil-fuel-derived greenhouse gas CO2 in urban areas

A novel fossil fuel pollution indicator based on the 13C/12C isotopic composition of plants has been designed. This bioindicator is a promising tool for future mapping of the sequestration of fossil fuel CO2 into urban vegetation. Theoretically, plants growing in fossil-fuel-CO2-contaminated areas, such as major cities, industrial centers, and highway borders, should assimilate a mixture of global atmospheric CO2 of delta13C value of -8.02 per thousand and of fossil fuel CO2 of average delta13C value of -27.28 per thousand. This isotopic difference should, thus, be recorded in plant carbon. Indeed, this study reveals that grasses growing near a major highway in Paris, France, have strikingly depleted delta13C values, averaging at -35.08 per thousand, versus rural grasses that show an average delta13C value of -30.59 per thousand. A simple mixing model was used to calculate the contributions of fossil-fuel-derived CO2 to the plant tissue. Calculation based on contaminated and noncontaminated isotopic end members shows that urban grasses assimilate up to 29.1% of fossil-fuel-CO2-derived carbon in their tissues. The 13C isotopic composition of grasses thus represents a promising new tool for the study of the impact of fossil fuel CO2 in major cities.