Analysis of beta-casein-monopalmitin mixed films at the air-water interface

The surface pressure (pi)-area (A) isotherms and Brewster angle microscopy (BAM) images of monopalmitin and beta-casein mixed films spread on buffered water at pHs 5 and 7 and at 20 degrees C were determined as a function of the mass fraction of monopalmitin in the mixture (X). The structural characteristics and morphology of monopalmitin-beta-casein mixed films are dependent on surface pressure, pH, and monolayer composition. The prevalence of monopalmitin in the interface increases with the amount of monopalmitin in the mixture and at higher pi. At the monopalmitin monolayer collapse the mixed film is practically dominated by the presence of monopalmitin. However, some degree of interactions exist between monopalmitin and beta-casein in the mixed film, and these interactions are more pronounced as the monolayer is compressed at the highest surface pressures.     

Nitrosation of phenolic compounds: inhibition and enhancement

The nitrosation of phenol, m-, o-, and p-cresol, 2,3-, 3,5-, and 2, 6-dimethylphenol, 3,5-di-tert-butylphenol, 2,4,6-trimethylphenol, o-chlorophenol, and o-bromophenol was studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the products at 345 nm. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of an attack on the nitrosatable substrate by NO(+)/NO(2)H(2)(+), followed by a slow proton transfer. The finding of an isokinetic relationship supports the idea that the same mechanism operates throughout the series. The observed sequence of nitrosatable substrate reactivities is explained by (i) the preferred para-orientation of the hydroxyl group for the electrophilic attack of nitrosating agents, (ii) steric hindrance of alkyl substituents, which reduces or prevents attack by nitrosating agents, and (iii) the hyperconjugative effect of the methyl substituent, which causes electronic charge to flow into the aromatic nucleus, as well as the opposite electronic withdrawing effect induced by halogen substituents. The results show that potential nitrosation of widespread environmental species such as chlorophenols is negligible, but more attention should be paid to polyphenols with strongly nucleophilic carbon atoms.     

Adsorption of whey protein isolate at the oil-water interface as a function of processing conditions: a rheokinetic study

In this paper we present surface dynamic properties (interfacial tension and surface dilational properties) of a whey protein isolate with a high content of beta-lactoglobulin (WPI) adsorbed on the oil-water interface as a function of adsorption time. The experiments were performed at constant temperature (20 degrees C), pH (5), and ionic strength (0.05 M). The surface rheological parameters and the interfacial tension were measured as a function of WPI concentration (ranging from 1 x 10(-)(1) to 1 x 10(-)(5)% w/w) and different processing factors (effect of convection and heat treatment). We found that the interfacial pressure, pi, and surface dilational modulus, E, increase and the phase angle, phi, decreases with time, theta, which should be associated with WPI adsorption. These phenomena have been related to diffusion of the protein toward the interface (at short adsorption time) and to the protein unfolding and/or protein-protein interactions (at long-term adsorption) as a function of protein concentration in solution and processing conditions.     

When structure means conservation: Effect of aggregate structure in controlling microbial responses to rewetting events

Rewetting events after a drought produce a pulse of soil respiration (the “Birch Effect”) that leads to a loss of carbon from soil, especially in Mediterranean ecosystems. Two main hypotheses have developed to explain the Birch effect: the “metabolic explanation”, based on the rapid consumption of intracellular osmolytes previously accumulated to survive to dry conditions, and the “physical explanation”, based on the consumption of carbon made accessible by physical destruction of internal structures of the soil.Here, we compared the respiration response of intact and crushed 9–4 mm aggregates from a California grassland soil under two different rewetting schemes: (1) successive short dry/wet events and (2) increased drought periods followed by a single rewetting. In intact aggregates, both microbial biomass and respiration rates were relatively stable through both experimental treatments. In crushed aggregates, through multiple short dry/wet cycles, both respiration rate and microbial biomass increased, while as drought length increased, biomass was unaffected but the magnitude of the following rewetting pulse increased. A mechanism that explains both these results is that crushing aggregates exposes occluded particular material that must be degraded into an immediately bioavailable form for microbes to take it up and metabolize it. Nitrification was generally higher in intact than crushed aggregates, suggesting the importance of physical association between nitrifiers and resources in regulating overall soil nitrification.This work suggests that physical processes are most important in driving respiration pulses through multiple rewetting cycles and that the physical association of organisms, substrates, and mineral particles are critical in controlling the functioning of the “microbial landscape”.     

Effect of calcium on the oxidation of linoleic acid by potato (Solanum tuberosum var. Desiree) tuber 5-lipoxygenase

When the effect of calcium on the oxidation of linoleic acid by potato tuber 5-lipoxygenase (LOX) was investigated, it was seen to promote the enzyme's activity at pH values higher than the optimum pH of 6.3, resulting in an enzyme activation at alkaline pH. Kinetic analysis of calcium activation at different pH values revealed that the cation abolished the inhibition by high substrate concentration, which occurs in the absence of Ca(2+), thus leading to activation at high substrate concentration. Studies were conducted to investigate the influence of Ca(2+) on the physicochemical nature of the substrate and its effect on the LOX activity expression. It was concluded that the aggregation mode rather than the aggregation state of linoleic acid is responsible for potato 5-LOX changes.     

Separation of olive proteins combining a simple extraction method and a selective capillary electrophoresis (CE) approach: application to raw and table olive samples

A simple extraction method was developed to extract proteins from olive samples based on chloroform/methanol extraction followed by a protein precipitation with cold acetone. Then, a capillary electrophoresis (CE) method was carried out using an acid buffer (1 M formic acid at pH 2) to ensure a positive net charge for proteins and a neutral charge for potential interferents as polyphenols. The method developed was applied to raw and table olive samples. Interestingly, raw olive samples showed differences in protein profiles depending upon the botanical variety of olives and their geographical region. Protein profiles obtained for table olives also showed differences according to the sample treatment. Thus, a signal reduction in the electropherograms obtained for black olives was observed in comparison to those achieved for treated green olives. In this work, the use of protein profiles was demonstrated to be a powerful tool for studying variations among olive samples.     

The genetic diversity associated with seed proteins in a collection of Spanish underground vetches (<Emphasis Type="Italic">Vicia sativa</Emphasis> L. subsp. <Emphasis Type="Italic">amphicarpa</Emphasis> (Dorthes) Asch. et Graebn.)

The characterization of plant genetic resources is the first step towards improving their use. The Spanish Plant Genetic Resources Centre, which belongs to the National Institute for Agricultural and Food Technology Research (CRF-INIA), conserves accessions of wild underground vetches collected in Spain. In the present work, 26 underground vetch accessions were characterized in terms of their seed storage proteins (separated by SDS-PAGE) as a means of assessing the genetic variation of these plants and their agronomic value. Vicia sativa cv. Vereda was used as control. A total of 54 bands were detected, of which 49 were polymorphic. Fifty eight different electrophoretic patterns were observed in total. Protein bands were scored in terms of their presence (1) or absence (0) for all the seeds studied, and two matrices constructed, one with all the bands present in each accession, the other with the different patterns for each accession. Dendrograms based on the Jaccard similarity index and the UPGMA clustering method were produced from these matrices, and the degree of genetic variation between and within accessions was calculated. The groups obtained were compared with the chromosome number for each accession. The results reflect the great diversity of underground vetch seed storage proteins. The aerial and underground seeds of 16 accessions were then analysed separately. In some cases, the aerial and underground flowers of the same plant produced different proteins.     

First indications for the involvement of strigolactones on nodule formation in alfalfa (Medicago sativa)

Strigolactones have recently been suggested to be phytohormones that are present in all plants. Strigolactones are released by roots into the rhizosphere, stimulating the seed germination of parasitic plants such as Striga spp. and Orobanche spp. and play a crucial role in the interaction between plants and symbiotic arbuscular mycorrhizal fungi.By applying different concentrations of the synthetic strigolactone analogue GR24 to alfalfa (Medicago sativa) inoculated with Sinorhizobium meliloti we could show that in alfalfa nodulation is positively affected by the presence of the strigolactone analogue GR24. Moreover, we could show that this increased nodulation cannot be linked with a stimulatory effect of GR24 on the growth or the expression of nod genes of S. meliloti.Putative mechanisms operating in the plant in response to the addition of GR24 and leading to increased nodule formation by rhizobia are discussed.     

Emissions of CO2, CH4 and N2O from Southern European peatlands

Peatlands play an important role in emissions of the greenhouse gases CO₂, CH₄ and N₂O, which are produced during mineralization of the peat organic matter. To examine the influence of soil type (fen, bog soil) and environmental factors (temperature, groundwater level), emission of CO₂, CH₄ and N₂O and soil temperature and groundwater level were measured weekly or biweekly in loco over a one-year period at four sites located in Ljubljana Marsh, Slovenia using the static chamber technique. The study involved two fen and two bog soils differing in organic carbon and nitrogen content, pH, bulk density, water holding capacity and groundwater level. The lowest CO₂ fluxes occurred during the winter, fluxes of N₂O were highest during summer and early spring (February, March) and fluxes of CH₄ were highest during autumn. The temporal variation in CO₂ fluxes could be explained by seasonal temperature variations, whereas CH₄ and N₂O fluxes could be correlated to groundwater level and soil carbon content. The experimental sites were net sources of measured greenhouse gases except for the drained bog site, which was a net sink of CH₄. The mean fluxes of CO₂ ranged between 139 mg m⁻² h⁻¹ in the undrained bog and 206 mg m⁻² h⁻¹ in the drained fen; mean fluxes of CH₄ were between −0.04 mg m⁻² h⁻¹ in the drained bog and 0.05 mg m⁻² h⁻¹ in the drained fen; and mean fluxes of N₂O were between 0.43 mg m⁻² h⁻¹ in the drained fen and 1.03 mg m⁻² h⁻¹ in the drained bog. These results indicate that the examined peatlands emit similar amounts of CO₂ and CH₄ to peatlands in Central and Northern Europe and significantly higher amounts of N₂O.