Ability of various water‐insoluble fertilizers to supply available phosphorus in hydroponics to plant species with diverse phosphorus‐acquisition efficiency: Involvement of organic acid accumulation in plant tissues and root exudates

Previous studies describe the suitability of a new type of phosphorus (P) fertilizer, called “rhizosphere‐controlled fertilizer” (RCF), to supply available P to plants while reducing soil phosphorus fixation. In order to explore the involvement of organic acid root exudation in P uptake from RCF, we investigated the relationship between shoot and root P concentrations, and the concentration of the main polycarboxylic organic acids in roots, shoots, and plant exudates. Plant species with different P‐acquisition efficiency (low: maize; medium: chickpea; high: lupin) were grown in hydroponics with three different P fertilizers: The water‐insoluble P fraction of RCF (RCF); Phospal, a slow‐release source of phosphate composed of calcium and aluminum phosphates (PH); monopotassiumphosphate (KP), and a control treatment without P (P–). RCF was as efficient as KP in supplying P to plants in the case of chickpea and lupin, and slightly less efficient than KP in maize. However, P from PH was not available for maize and less available compared to KP and RCF in chickpea and lupin. This variation reflects the different efficiencies in P acquisition for the three plant species. Except in the case of maize, plants receiving KP presented the lowest concentration of organic acids in roots and exudates, while those plants suffering severe P deficiency (P– and PH) showed the highest organic acid concentration. However, RCF had a high concentration of organic acids in roots and exudates, as well as a high P concentration in the shoot indicating that P uptake from RCF is enhanced due to root release and action of specific organic acids.     

Uncertainties associated with trophic discrimination factor and body size complicate calculation of δ15N-derived trophic positions in Arapaima sp.

Stable isotope ratios of nitrogen (δ¹⁵N) have been used to estimate trophic position (TP) of organisms due to the predictable enrichment of nitrogen-15 in consumer tissues relative to their diet. We explored estimates of trophic position using liver and muscle δ¹⁵N and stomach content analysis in a broad size range of Arapaima sp. from Amazonian floodplain lakes. Estimates of TP based on liver δ¹⁵N were more closely related to the stomach content data than estimates based on muscle δ¹⁵N, possibly because of the higher turnover of nitrogen in liver. Total length and season explained most of the variation in TP values estimated from δ¹⁵N, showing that they have more effect than prey trophic position on δ¹⁵N values. The TP estimated by identification of stomach content was 3.6 and was unrelated to the size of the arapaima. This highlights the need for a better understanding of the factors that affect values of δ¹⁵N and stomach content analysis is still needed to unravel the trophic ecology of predatory fishes.     

Environmental and spatial processes: what controls the functional structure of fish assemblages in tropical rivers and headwater streams?

In this study, we investigated functional structure patterns of tropical headwater and river fish assemblages. We hypothesised that environmental conditions are primarily structuring headwater streams leading to functionally clustered assemblages, whereas processes that favour functional overdispersion would guide river assemblages. For 27 headwater streams and 22 rivers, we used eight functional traits for calculating two functional indexes: mean pairwise distance (MPD) and net relatedness index (NRI). We performed linear regressions between indexes and species richness, a multiple regression between NRI and eight environmental variables and a variation partitioning to disentangle the role of environment and space on NRI. Our findings indicate that fish assemblages of headwaters are structured by environmental conditions as most assemblages in this habitat displayed a tendency to clustering and MPD/NRI were not correlated with species diversity, whereas the opposite pattern was observed for river habitat. Four environmental variables (channel depth, water velocity, dissolved oxygen and turbidity) explain 56% of functional structure variation. These variables seem to function as selective filters in headwaters, whereas channel depth may be determinant for functional overdispersion of river fish assemblages. Components associated with space are also influencing the functional structure. Limitations of species dispersal through space (between both habitat types) appear as a possible cause to this. In this sense, both environmental conditions and processes linked with space are capable of influencing the functional structure of tropical headwater streams and river fish assemblages.     

Metabolism of oak leaf ellagitannins and urolithin production in beef cattle

Oak leaves have a high concentration of ellagitannins. These phytochemicals can be beneficial or poisonous to animals. Beef cattle are often intoxicated by oak leaf consumption, particularly after suffering feed restriction. The severity of the poisoning has recently been associated with the ruminal microbiota, as different bacterial populations were found in animals that tolerated oak leaves and in those that showed clinical and pathological signs of toxicity. Intoxication has previously been linked to the production of phenolic metabolites, particularly catechol, phloroglucinol, and resorcinol. This suggested that the microbial metabolism of ellagitannins could also be associated with its tolerance or intoxication in different animals. Therefore, it is essential to understand the metabolism of ellagitannins in cattle. Here we show that ellagitannins are metabolized in the cattle rumen to urolithins. Different urolithins were detected in ruminal fluid, feces, urine, and plasma. Oak leaf ellagitannins declined as they were converted to urolithins, mainly isourolithin A and urolithin B, by the ruminal and fecal microbiota. Urolithin aglycons were observed in rumen and feces, and glucuronide and sulfate derivatives were detected in plasma and urine. Sulfate derivatives were the main metabolites detected in plasma, while glucuronide derivatives were the main ones in urine. The main urolithins produced in cattle were isourolithin A and urolithin B. This is a relevant difference from the monogastric mammals studied previously in which urolithin A was the main metabolite produced. Low molecular weight phenolics of the benzoic, phenylacetic, and phenylpropionic groups and metabolites such as catechol, resorcinol, and related compounds were also detected. There was a large variability in the kinetics of production of these metabolites in individual animals, although they produced similar metabolites in all cases. This large variability could be associated with the large variability in the rumen and intestine microbiota that has previously been observed. Further studies are needed to demonstrate if the efficiency in the metabolism of ellagitannins by the microbiota could explain the differences observed in susceptibility to intoxication by the different animals.     

Impact of high-pressure processing on vitamin E (α-, γ-, and δ-tocopherol), vitamin D (cholecalciferol and ergocalciferol), and fatty acid profiles in liquid foods

In the present study, four high-pressure (HP) treatments (100, 200, 300, and 400 MPa) of 9 min duration were evaluated to assess their effect on the lipid fraction (fat-soluble vitamins and fatty acid profile) of an orange juice-milk and a vegetable beverage. After HP treatment, nonsignificant changes in vitamin D(2) and D(3) contents were observed for both beverages. An increase in vitamin E activity was observed in HP beverages when pressures >100 MPa were applied, mainly due to an increase in α-tocopherol content. Only a small reduction in fat content was found for the orange juice-milk beverage, but no changes were observed for the vegetable beverage. A significant decrease in SFA levels was observed in HP-treated (300-400 MPa) orange juice-milk. With regard to MUFA, a significant increase in oleic acid (C(18:1)) was found in both liquid foods. Nonsignificant differences in the PUFA profiles were observed after HP processing.     

Preparation of antibodies and development of an enzyme-linked immunosorbent assay (ELISA) for the determination of doxycycline antibiotic in milk samples

This paper reports the development of an immunoassay for the specific analysis of doxycycline (DC), a congener of the tetracycline antibiotic family (TCs), in milk samples. This is the first time that DC antibody production is reported, based on a rationally designed and well-characterized immunizing hapten. The chemical structure of the immunizing hapten (13-[(2-carboxyethyl)thiol]-5-hydroxy-6-α-deoxytetracycline, TC1) was designed to maximize recognition of the tetracycline characteristic moiety defined as lower periphery of the TCs plus the region of the upper periphery composed by the hydroxyl group at position C(5) (B ring) and the dimethylamino group in ring A. Polyclonal antibodies raised against TC1 coupled to horseshoe crab hemocianyn (HCH) were used to develop a homologous indirect competitive enzyme-linked immunosorbent assay (ELISA). The microplate ELISA can detect DC in buffer down to 0.1 μg L(-1). The ELISA has been proven to tolerate a wide range of ionic strengths and pH values. The assay is very selective for DC with a minor recognition of methacycline (32% of cross-reactivity). Experiments performed with whole milk samples demonstrate that samples can be directly analyzed after a simple treatment method, reaching detectability values below 5 μg L(-1).     

Action of tyrosinase on ortho-substituted phenols: possible influence on browning and melanogenesis

The action of tyrosinase on ortho-substituted monophenols (thymol, carvacrol, guaiacol, butylated hydroxyanisole, eugenol, and isoeugenol) was studied. These monophenols inhibit melanogenesis because they act as alternative substrates to L-tyrosine and L-Dopa in the monophenolase and diphenolase activities, respectively, despite the steric hindrance on the part of the substituent in ortho position with respect to the hydroxyl group. We kinetically characterize the action of tyrosinase on these substrates and assess its possible effect on browning and melanognesis. In general, these compounds are poor substrates of the enzyme, with high Michaelis constant values, K(m), and low catalytic constant values, k(cat), so that the catalytic efficiency k(cat)/K(m) is low: thymol, 161 ± 4 M(-1) s(-1); carvacrol, 95 ± 7 M(-1) s(-1); guaiacol, 1160 ± 101 M(-1) s(-1).     

Development and characterization of silver-based antimicrobial ethylene-vinyl alcohol copolymer (EVOH) films for food-packaging applications

The use of silver as an antimicrobial in the food area has raised wide interest in recent years. In the present work, 0.001-10 wt % silver ions was satisfactorily incorporated into an ethylene-vinyl alcohol (EVOH) copolymer matrix by a solvent casting technique. The antibacterial efficacy of the composite was evaluated under laboratory conditions and in contact with some foods. The ionic compound did not affect the crystallinity or the water-induced plasticization of the materials and was homogeneously distributed across the surface and thickness of the films. When immersed in water, sorption-induced release of 50-100% of the silver ions took place in <30 min. In the bacterial minimal growth medium M9, the minimal inhibitory concentration (MIC) of the film was in the range of 0.01-0.1 ppm. High protein content food samples displayed low susceptibility to the films (<1 log reduction in any case), whereas low protein content food samples exhibited no detectable bacterial counts for films with 1 and 10 wt % silver and about 2 log reduction for films with 0.1 wt % silver. These results represent a step forward in the understanding of silver antimicrobial efficacy and its possible application in the food-packaging industry, most likely as food coatings.     

Effect of the chlorinated washing of minimally processed vegetables on the generation of haloacetic acids

Chlorine solutions are usually used to sanitize fruit and vegetables in the fresh-cut industry due to their efficacy, low cost, and simple use. However, disinfection byproducts such as haloacetic acids (HAAs) can be formed during this process, which can remain on minimally processed vegetables (MPVs). These compounds are toxic and/or carcinogenic and have been associated with human health risks; therefore, the U.S. Environmental Protection Agency has set a maximum contaminant level for five HAAs at 60 μg/L in drinking water. This paper describes the first method to determine the nine HAAs that can be present in MPV samples, with static headspace coupled with gas chromatography-mass spectrometry where the leaching and derivatization of the HAAs are carried out in a single step. The proposed method is sensitive, with limits of detection between 0.1 and 2.4 μg/kg and an average relative standard deviation of ～8%. From the samples analyzed, we can conclude that about 23% of them contain at least two HAAs (<0.4-24 μg/kg), which showed that these compounds are formed during washing and then remain on the final product.