Heat treatment of beta-lactoglobulin: structural changes studied by partitioning and fluorescence

Functional properties of whey protein concentrates (WPC) are primarily dependent on the degree of denaturation of beta-lactoglobulin (beta-LG), the major globular whey protein. Irreversible modifications in the tertiary structure and association state of beta-LG after heat treatment were studied by partition in aqueous two-phase systems and fluorescence quenching. Partitioning of preheated beta-LG in two-phase systems containing 5% (w/w) poly(ethylene glycol) and 7% (w/w) dextran, between pH 6.0 and7.0, are appropriately related with the intensity of heat treatment. An increase in the partition coefficient of beta-LG was observed with increasing temperature of heat treatment. On the other hand, fluorescence quenching of beta-LG by acrylamide was used to study the conformational flexibility of the protein at pH values between 4. 0 and 9.0. The values of bimolecular quenching rate constant (k(q)) obtained showed that beta-LG appears to be more flexible at high pH values, while at low pH the protein assumes a more compact form. The efficiency of acrylamide quenching on preheated beta-LG was substantially more pronounced than for the untreated protein. This difference can be ascribed to the presence of unfolded monomers and aggregates of denatured molecules formed after heat treatment, whose tryptophanyl residues are more exposed to the solvent. In conclusion, the results suggest that partition studies in aqueous two-phase systems and fluorescence quenching are very useful tools to detect changes in conformation and aggregation of beta-LG induced by heat treatment.     

Effect of the addition of sewage sludge as a fertilizer on a sandy vineyard soil

Purpose

The application of sludge from wastewater in agriculture has increased in recent years, and it is therefore important to assess the effect that such treatment has on both the soil and the plant. The aim of the study described here was to ascertain whether there is a variation in the properties of the soil and to determine if this addition has an impact on the plant.

Materials and methods

The area of investigation was close to the municipality of Villarrubia de los Ojos (Ciudad Real). In this work, six samples were taken from the surface horizon in the studied plot at a depth of 35 cm. A further three samples were taken: (i) a surface horizon of a soil close to the area under investigation but without treatment (control sample), (ii) a sample of sludge from the wastewater treatment plant and (iii) a sample of the mixture used by farmers as fertilizer. Laboratory tests were conducted in accordance with the SCS-USDA (1972) guidelines. Trace element samples were analysed by X-ray fluorescence spectrophotometry (Philips PW 2404).

Results and discussion

The parcel of land studied is dominated by a sandy texture (88.3 % sand), and a decrease in pH was observed in areas in which the mixture (manure + sludge) was added (pH?=?8.0) compared to areas in which fertilizer was not applied (pH?=?8.5). It was observed that the addition of the compound led to an increase in the electrical conductivity of the soil. The trace elements can be organized into two groups based on the results obtained in this study. One group contains the trace elements that were only present in the rows that were treated with the fertilizer. The other group of trace elements was mobilized throughout the whole plot.

Conclusions

The application of sewage sludge on agricultural soils can be very useful as an organic amendment because it produces an increase in soil organic matter. However, sewage sludge must be applied with caution due to the changes in soil chemical properties (for example, pH and E.C.). The use of this type of waste for prolonged periods of time can cause problems of contamination in the soil.

     

Arsenic,lead, and uranium concentrations on sediments deposited in reservoirs in the Rio Grande Basin,USA–Mexico border

Purpose

The El Granero reservoir is the last reservoir of the Rio Conchos before it joins the Rio Grande at the Mexico–USA border. This reservoir, together with the San Marcos reservoir, is located in the arid region of Chihuahua, Mexico. High, naturally occurring radioactivity levels, as well as high arsenic (As) concentrations, have been found in both reservoirs. The main goal of this research was to establish the spatial and temporal distribution of trace and radioactive elements in surface sediments and cores collected from these reservoirs.

Materials and methods

Sediment cores were dated using ²¹⁰Pb and ¹³⁷Cs measurements and applying the constant rate of supply (CRS) model. Major, trace, and radioactive elements were determined in surface samples and three sediment cores. Radioactive elements were determined by both alpha and gamma spectrometry. Major and trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using the EPA 3051a method. Enrichment factors (EF), contamination factors (CF), and pollution load indexes (PLI) were calculated in order to identify the human impact in both reservoirs, whereas the chemical index weathering (CIW) was used to assess differences in the degree of weathering.

Results and discussion

High uranium (U) enrichment (EFs?=?24.9–54.7) was observed in core layers at the San Marcos reservoir, while in surface sediments, this enrichment was lower. The high variability of lead (Pb) and As in sediment cores from the Granero reservoir was attributed to human influence. Arsenic and Pb enrichment differences between entry and exit sediment cores were explained by the filtering capabilities of the elongated shape, the topography, and the presence of plants on the reservoir’s bed. The highest PLI was found at the entrance core of the Granero reservoir.

Conclusions

The natural element concentration levels of As, Pb, and U were established at the Granero reservoir. High EFs for As and Pb suggest an anthropogenic origin of these pollutants at specific time intervals. High U concentrations in the San Marcos area are explained as naturally occurring. The concentrations of As in most of the studied sediments could pose a risk to human health by As ingestion, since they are above the probable effect level (PEL).

     

Determination of Plant-Available Nutrients in Two Wood Ashes: The Influence of Combustion Conditions

Wood ashes were traditionally used as a fertilizing agent from the very beginning of working land but the fertilizing quality varies according to the combusted biomass and also the industrial burning equipment. The differences between wood ash originated from fluid and classic boiler were investigated by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), and Mehlich 3 and deionized water extraction procedures in relation to extraction time. The results, especially of the SEM and chemical extractions, have demonstrated that the type of burning boiler determines the portions of the leachable nutrient elements. The silica and alumina ash content conducted by the elevated temperature transforms the main proportion of calcium and potassium into the insoluble feldspars. Due to this effect only a small amount of nutrients could be released and served as a fertilizing matter.     

1,2,4-Trichlorobenzene Flow Characteristics in Saturated Homogeneous and Stratified Porous Media

Aerosol samples were continuously collected at Rishiri Island, Japan and concentrations of trace metals and water-soluble ionic constituents in the aerosol samples were measured in this study. Trace metal concentrations were analyzed by using inductively coupled plasma mass spectrometry equipped with a laser ablation sample introduction (LA/ICP-MS), which is a rapid and simultaneous method for multi-element analysis. The average concentrations of trace metals and water-soluble ionic constituents in TSP at Rishiri Island from March 2001 to October 2003 were: Al: 251 ± 371 (n= 359), Ti: 27 ± 38 (n= 342), V: 1.3 ± 1.6 (n= 327), Cr: 2.0 ± 2.2 (n= 202), Mn: 8.6 ± 12.0 (n= 353), Fe: 356 ± 645 (n= 349), Co: 0.18 ± 0.25 (n= 250), Ni: 1.9 ± 3.4 (n= 232), Cu: 7.4 ± 10.2 (n= 123), Zn: 16 ± 20 (n= 242), As: 1.2 ± 2.1 (n= 312), Se: 0.49 ± 0.65 (n= 133), Cd: 0.19 ± 0.33 (n= 285), Sb: 0.46 ± 0.62 (n= 265), Pb: 16 ± 30 (n= 314), Na⁺: 1153 ± 1384 (n= 306), NH₄ ⁺: 247 ± 257 (n= 254), K⁺: 74 ± 63 (n= 284), Ca²⁺: 144 ± 174 (n= 294), Mg²⁺: 150 ± 161 (n= 293), Cl^?: 2703 ± 3151 (n= 180), NO₃ ^?: 339 ± 415 (n= 332), SO₄ ^2?: 1648 ± 1398 (n= 362) (unit: ng m^?3). The obtained trace metal concentration levels in the aerosol were 1/10–1/70 of those obtained at Beijing, China and 1/2–1/40 of those obtained at Tokyo, Japan. The correlation between Al, Ti, Mn, and Fe, which were derived mainly from soil dust, was high at Rishiri Island. High-concentration events (when the measured value exceeds the average +3σ for the entire observation period) for each chemical constituent were observed several times per year, although the chemical concentration levels in TSP at Rishiri Island were almost constant throughout the year. The high-concentration phenomenon, which occurred in only 2% of the measurement days, raised the average concentration of the atmospheric chemical constituents at Rishiri Island by about 10%. The average value of the Pb/Zn ratio at Rishiri Island during the entire period was 1.8 ± 2.9, which is higher than 1. This suggests that the atmosphere at Rishiri Island has constantly been receiving contaminants from the Asian Continent. We conclude that the chemical constituents in the aerosol at Rishiri Island have been regularly transported from a wide area across the Asian Continent.     

Remediation of As-Contaminated Soils in the Guadiamar River Basin (SW, Spain)

In 1998, the pond containing the ore wastes from a pyrite mine in Aznalcóllar (SW, Spain) broke open, spilling some 36×10⁵ m³ of acidic waters and 9?×?10⁵ m³ of tailings containing high concentrations of As and heavy metals. The affected area was around 55 km² of predominantly agricultural soils. After the clean-up of the tailings, many remediation actions were undertaken and the use of blocking agents to immobilize the As was one of the most extended measure. The first experiment performed was to determine the most important soil components in As adsorption under acidic conditions. A second experiment was conducted to neutralize the acidity caused by the solution coming from the tailings undergoing oxidation; an adequate liming material (sugar-refinery scum) was selected and the application rates were established. After the remediation measures, the zone was monitored for three years. A detailed study in four experimental plots located in the most polluted sector was carried out to test the influence of iron oxides in the As immobilization. The use of red soils of the area (rich in free-iron oxides Fe_d) was established as an appropriate material in the remediation of the area.     

Influence of mycorrhiza vs. soluble phosphate on growth,nodulation, and N2 fixation (15N) in alfalfa under different levels of water potential

Summary The legume Medicago sativa (+Rhizobium melilott) was grown under controlled conditions to study the interactions between soluble P in soil (four levels), or a mycorrhizal inoculum, and the degree of water potential (four levels) in relation to plant development and N₂ fixation. ¹⁵N-labelled ammonium sulphate was added to each pot for a qualitative estimate of N₂ fixation, in order to rank the effects of the different treatments.Dry-matter yield, nutrient content and nodulation increased with the amount of plant-available P in the soil, and decreased as the water stress increased, for each P-level. The mycorrhizal effect on dry matter, N yield, and on nodulation was little affected by the water potential. Since P uptake was affected by the water content in mycorrhizal plants, additional mechanisms, other than those mediated by P, must be involved in the mycorrhizal activity.There was a positive correlation between N yield and nodulation for the different P levels and the mycorrhizal treatment at all water levels. A high correlation between plant unlabelled N content and atom% ¹⁵N excess was also found for all levels of P. In mycorrhizal plants, however, the correlation between unlabelled N yield and ¹⁵N was lower. This suggests that mycorrhiza supply plants with other N sources in addition to those derived from the improvement on N₂ fixation.     

Gypsum Precipitation – A Medium to Control Sulphate Pollution of Freshwater Sediment Leachates

To treat sulphate pollution resulting from freshwater sediments,an experimental study was done. This experimental study was carried out to determine the effects of pH values and calcium supplements (as CaCl₂) on the formation of gypsum in a representative wetland sediment that was aerated. It was foundthat the differences between dissolved sulphate in untreatedcontrol and the other treatments with CaCl₂ amendments canbe attributed to the precipitation of gypsum. At the same time, the system was highly affected by Ca adsorption/desorption thatwas controlled by pH values. ECOSAT equilibrium simulations showed that CaCl₂ additions (0.2–0.3 mol L^-1) to aerated freshwater sediment resulted in removal of 78–98% ofsulphate (from its total content) from the solution. It wascaused by favourable conditions for gypsum formation i.e. acidicpH values were not increased due to the neutral character of CaCl₂. On the contrary to CaCl₂ amendments, CaCO₃supplements (in the same Ca doses as applied in CaCl₂) caused the removal of only 5–25% of sulphate. The significantincrease of pH values after the application of CaCO₃ limitedgypsum formation due to high saturation of the system with CO₃ ^-2 and HCO₃ ^-. It resulted in the prevalence of CaCO₃ formation in this system. However, theaddition of Cl^- can facilitate the mobilisation of cationicmetals like Cd and Pb in the form of Cl^--complexes. Therefore, CaCl₂ treatment should be used in the sites thatdo not contain elevated amounts of these metals.     

Browning evaluation of ready-to-eat apples as affected by modified atmosphere packaging

The color and polyphenol oxidase (PPO) activity of fresh-cut Golden delicious apples were evaluated throughout cold storage under modified atmospheres. The shelf life of cut apples was extended to several weeks, especially when an initial atmosphere of 90.5% N(2) + 7% CO(2) + 2.5% O(2) and plastic pouches of 30 cm(3)/cm(2) x bar x 24 h were used. Under these conditions, a maximum 62% PPO activity depletion was observed. In all cases, the faster the initial PPO activity decays, the less the color changes. A fractional conversion first-order model was proposed for predicting color changes in minimally processed apples. Browning was better described through lightness (L) (k(L) = 0.017 - 0.07 day(-1)) and color difference (Delta E*) values (k(Delta E) = 0.015 - 0.073 day(-1)), which fitted the model with enough accuracy.     

Physiological and nutritional responses by Lactuca Sativa L. to nitrogen sources and mycorrhizal fungi under drought conditions

We measured the growth, nutrition, and N assimilation of arbuscular-mycorrhizal and non-mycorrhizal lettuce (Lactuca sativa L.) as affected by forms of N and drought. Moisture was maintained at 80% water-holding capacity, and N was applied as NO _inf3 ^sup- , NH _inf4 ^sup+ , or NO _inf3 ^sup- /NH _inf4 ^sup+ (3:1, 1:1, or 1:3). The growth of Glomus fasciculatum-colonized plants was comparable to that of uncolonized P-supplemented plants when N was provided as NH _inf4 ^sup+ or combined NO _inf3 ^sup- /NH _inf4 ^sup+ . When N was supplied solely as NO _inf3 ^sup- , G. fasciculatum-colonized plants produced a higher yield than P-fertilized plants, suggesting that the uptake and/or assimilation of NO _inf3 ^sup- was particularly affected by mycorrhizal status in this water-limited situation. Nutrient availability, except Ca, was less limited for mycorrhizal plants than for P-fertilized plants. P fertilization increased the growth, glutamine synthetase activity, and protein content of lettuce to the same extent that G. fasciculatum colonization did when N was applied as NH _inf4 ^sup+ . With NO _inf3 ^sup- -fertilization, G. fasciculatum-colonized plants showed increased growth, nitrate reductase activity, and protein content compared to P-fertilizer treatment. Plants colonized by G. mosseae showed increased photosynthetic activity and proline acumulation, and these mechanisms may be important in adaptation by the plant to drought conditions. The present results confirmed that under drought conditions, the uptake or metabolism of N forms is particularly affected in mycorrhizal fungi-colonized plants, depending on the mycorrhizal endophyte and the N source added. Thus the significance of arbuscular-mycorrhizal fungus selection for plant growth in drought conditions is a consideration for management strategy.