Interaction between casein micelles and whey protein/κ-casein complexes during renneting of heat-treated reconstituted skim milk powder and casein micelle/serum mixtures

Casein micelles were separated from unheated reconstituted skim milk powder (RSMP) and were resuspended in the serum of RSMP that had been heated, with and without dialysis of this serum against unheated RSMP. Using size-exclusion chromatography, it was found that the soluble complexes of whey protein (WP) with κ-casein in the serum of the heated milk bind progressively to unheated casein micelles during renneting, even prior to the onset of clotting. Similar trends were noted when casein micelles from RSMP heated at pH values of 6.7, 7.1, or 6.3, each with different amounts of WP coating the micelles, were renneted in the presence of soluble WP/κ-casein complexes. No matter what was the initial load of micelle-bound WP complexes, all micelle types were capable of binding additional serum protein complexes during renneting. However, it is not clear that this binding of WP/κ-casein complexes to the micellar surface is a direct cause of the impaired rennet clotting of the RSMP.     

Genetic diversity of bacterial β-glucosidase-encoding genes as a function of soil management

This study is the first approach to evaluate the diversity of bacterial β-glucosidase-encoding gene sequences, aiming to identify the main environmental factors structuring bacterial β-glucosidase genetic diversity in semiarid soils. Two agricultural management systems, soils under spontaneous cover vegetation vs. noncovered herbicide-treated soils, were tested. The weed biomass generated in the former was estimated around 2,600 kg?ha^?1?year^?1, whereas leaves and root exudates from olive trees were the only input of C biomass in the latter. Dendrograms generated from polymerase chain reaction–denaturing gradient gel electrophoresis profiles of bacterial β-glucosidase-encoding genes revealed two clusters determined by soil treatment and sharing <20 % similarity. The sequences of a total of 59 DNA fragments, representing 39 operational taxonomic units, were successfully determined. The Proteobacteria phylum clearly dominated all the soil samples, but representatives of Chloroflexi, Deinococci, Actinobacteria, Thermotogae, and Firmicutes class were also detected. Management strategies favoring the presence of spontaneous vegetation determined a higher genetic diversity of β-glucosidase-encoding genes of soil bacteria. However, since there is little information of β-glucosidase gene sequences available in databases, it is difficult to establish particular relationships between bacterial networks for C degradation and land use. Results from canonical correspondence analysis indicated that bacterial metabolic networks for oligomeric C substrates utilization were affected by the physicochemical properties of the soil; the uppermost 10 cm of covered soil clustered together and were positively correlated with some chemical properties related to soil fertility, whereas less influence of soil texture was observed for the deeper layers of bare soils.     

Effects of adding low levels of a disulfide reducing agent on the disulfide interactions of β-lactoglobulin and κ-casein in skim milk

Low concentrations of a disulfide reducing agent were added to unheated and heated (80 °C for 30 min) skim milk, with and without added whey protein. The reduction of the β-lactoglobulin and κ-casein disulfide bonds was monitored over time using electrophoresis. The distribution of the proteins between the colloidal and serum phases was also investigated. κ-Casein disulfide bonds were reduced in preference to those of β-lactoglobulin in both unheated and heated skim milk (with or without added whey protein). In addition, in heated skim milk, while the serum κ-casein was reduced more readily than the colloidal κ-casein, the distribution of κ-casein between the two phases was not affected.     

Relationships between sulfur concentration in mulberry Leaves and the quality of silkworm cocoon

A 40-day gnotobiotic microcosm experiment was carried out to quantify the effect of bacterial-feeding nematode on plat growth and nutrient absorption.The results showed that inoculation of bacterial-feeding nematode Protorhabditis sp.stimulated the growth of wheat (Triticum aestivum) and the uptake of N.By the end of the 40-day incubation wheat biomass and N uptake in the treatment with nematode and bacteria (Pseudomonas sp.)increased by 6.5% and 5.9%,respectively,compared with bacteria alone treatment.The presence of nematode mainly accelerated the growth of aboveground of wheat,while it slightly inhibited the root development.There was little difference in plant tissue N concentration between treatments.P concentration and uptake of wheat,however,were generally reduced by nematode, It appears that the enhancement of plant growth and nitrogen uptake is attributed to the enhancement of nitrogen mineraliztion induced by nematode feeding on bacteria,and the reduction of phosphorous uptake is the result of ewak root status and comptetition by bacteria immobilzation.     

Reactions between β-lactoglobulin and genipin: kinetics and characterization of the products

In this paper, we present the first detailed study of the reaction kinetics and the characterization of the products from the endothermic reactions between β-lactoglobulin and genipin. The effects of the concentration, temperature, and pH were investigated. In the temperature range studied, the reaction was approximately a pseudo-first-order with respect to genipin and 0.22-order and -0.24-order with respect to β-lactoglobulin for pH 6.75 and 10.5 with corresponding activation energy (E(a)) estimated to be 66.2 ± 3.8 and 9.40 ± 0.36 kJ/mol, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis studies, validated by matrix-assisted laser desorption ionization-time of flight mass spectrometry, showed the presence of oligomeric, i.e., di-, tri-, quadri-, and pentameric, forms of cross-linked β-lactoglobulin by genipin at neutral but not alkaline pH; however, an extensive cross-linked network was not observed, consistent with the atomic force microscopy images. It was demonstrated that the reaction temperature and the concentration of genipin but not that of β-lactoglobulin positively affected the extent of the cross-linking reactions.     

Comparison of the hydrolysis of bovine κ-casein by camel and bovine chymosin: a kinetic and specificity study

Bovine chymosin constitutes a traditional ingredient for enzymatic milk coagulation in cheese making, providing a strong clotting capacity and low general proteolytic activity. Recently, these properties were surpassed by camel chymosin, but the mechanistic difference behind their action is not yet clear. We used capillary electrophoresis and reversed-phase liquid chromatography-mass spectrometry to compare the first site of hydrolysis of camel and bovine chymosin on bovine κ-casein (CN) and to determine the kinetic parameters of this reaction (pH 6.5; 32 °C). The enzymes showed identical specificities, cleaving the Phe105-Met106 bond of κ-CN to produce para-κ-CN and caseinomacropeptide. Initial formation rates of both products validated Michaelis-Menten modeling of the kinetic properties of both enzymes. Camel chymosin bound κ-CN with ～30% lower affinity (K(M)) and exhibited a 60% higher turnover rate (k(cat)), resulting in ～15% higher catalytic efficiency (k(cat)/K(M)) as compared to bovine chymosin. A local, less dense negatively charged cluster on the surface of camel chymosin may weaken electrostatic binding to the His-Pro cluster of κ-CN to simultaneously impart reduced substrate affinity and accelerated enzyme-substrate dissociation as compared to bovine chymosin.     

Responses of a salt‐tolerant and a salt‐sensitive line of sunflower to varying sodium/calcium ratios in saline sand culture

The effects on two‐week‐old plants of a salt‐tolerant line (Euroflor) and a salt‐sensitive (SMH‐24) line of sunflower, of varying sodium/calcium (Na/ Ca) ratios in a saline growth medium were assessed after three weeks growth in sand culture under greenhouse conditions. The different Na/Ca ratios of the salt treatment were 36.5, 74.0, and 149, at a constant concentration of 150 mol m^‐3 NaCl. Euroflor was superior to SMH‐24 in fresh and dry matters of shoots and roots at varying external Na/Ca ratios. The leaf Na⁺ concentration in SMH‐24 increased consistently with increase in external Na/Ca ratio, whereas that in Euroflor remained almost unaffected. Although leaf chlorine (Cl^‐) was significantly greater in SMH‐24 than Euroflor, there was no effect of decreasing Ca²⁺ concentration of the saline growth medium on the leaf Cl^‐ concentrations of both lines. The lines did not differ in K⁺, Ca²⁺ or Mg²⁺ concentrations of both shoots and roots. The leaf K/Na and Ca/ Na ratios, K versus Na selectivity were considerably higher in Euroflor than in SMH‐24. The lines also did not differ in leaf water potential and gas exchange and these variables were not affected due to decreasing Ca²⁺ concentration of the saline growth medium. Stomatal conductance and transpiration remained unchanged in Euroflor, whereas those in SMH‐24 decreased significantly at the highest external Na/Ca ratio. Euroflor had significantly greater stomatal conductance and transpiration than those of SMH‐24 at almost all external Na/Ca ratios, whereas the reverse was true for water use efficiency. It was established that Euroflor was tolerant to low Ca²⁺ concentrations of the saline growth medium as compared with SMH‐24. This was mainly attributable to accumulation of relatively low Na⁺ and Cl^‐ in the leaves, and maintenance of high leaf K/Na and Ca/Na ratios and K versus Na selectivity in Euroflor.     

The relationship between applied nitrogen and the concentration of nitrate‐N in cotton petioles

Abstract

Cotton petioles from irrigated plants grown under varying nitrogen regimes were analyzed for nitrate‐N (NO₃‐N). The most recent, fully matured petioles were selected. The concentration of NO₃‐N in the petioles was related to applied N rates and the yields of lint obtained. The concentration of NO₃‐N for any given N application declined as the season progressed. The concentration of petiole nitrate increased at all sampling dates as the rate of applied N increased. The relationship between applied N and NO₃‐N concentrations was most predictable when samples were collected two weeks after the initiation of squaring. The influence of applied N on the concentration of petiole nitrate was also greatest at this stage. The diagnosis of either N deficiency or excess N would be feasible by petiole analysis when the effects of stage of growth could be separated from the effects of soil N.     

Occurrence of blossom‐end rot in tomato as a function of calcium dose in the nutrient solution and air relative humidity

The effects of different calcium (Ca) concentrations in the nutrient solution and of air relative humidity (RH) on the Ca levels and on the incidence of blossom‐end rot in tomato fruit cv. Jumbo were studied. The experiment was conducted in a greenhouse under hydroponic conditions using a modified Hoagland solution containing different Ca concentrations (0.2, 2.5, 5.0, 10.0, 15.0, and 20.0 mm L^‐1) which represented the different treatments. The trial was conducted in a fully randomized design with three replications, with Ca doses representing the plots and environments with high and low RH the subplots. The fruits of the second and third clusters were used, with two fruits per cluster, one maintained at high (90±5%) and the other at low (40±5%) RH. The fruits were picked after full ripening. A greater Ca accumulation was observed in fruits submitted to low RH with this accumulation occurring at all Ca levels in the solution. In the treatment with 100 mg Ca L^‐1, the plants died and did not reach fructification. The fruits of plants treated with 100 mg Ca L^‐1 and submitted to low RH had blossom‐end rot although their Ca levels were higher than those detected in the fruits of this treatment submitted to high RH. At this Ca dose, the seeds were small, malformed, and black. Our results show that fruit kept at low RH had higher Ca accumulation although the excessive water loss from tissues may lead to blossom‐end rot when low Ca doses are supplied to the plants.     

Potential nitrification, nitrate reductase, and β-galactosidase activities as indicators of restoration of ecological functions in a Zn-contaminated soil

The present study was conducted to assess the possible restoration of different ecological functions in a Zn-contaminated soil. Experiments were conducted in a soil microcosm contaminated with 350?mg?kg^?1 of Zn and in an uncontaminated control microcosm, both incubated for 4?months. At regular intervals, potential nitrification, nitrate reductase, and β-galactosidase activity were determined. All these activities were significantly reduced just after Zn contamination in contaminated microcosms compared to the activities of the control, but then increased. In order to confirm that the restoration of ecological functions was not due to an aging phenomenon, a reinoculation protocol was also applied. A significant restoration was found for β-galactosidase activity, while for nitrate reductase activity and potential nitrification, there was a clear shift of dose–response curves but with partial overlap of the EC₅₀ ranges estimation, thus indicating that different ecological functions are restored over time in Zn-contaminated soils.     

Tolerance of spring wheat to a salt‐fluxing residue containing potassium and magnesium

Abstract

Field and greenhouse studies were conducted in Idaho in 1985 to document the maximum levels of a salt fluxing residue (slag) material that can be safely applied to agricultural soils without reducing spring wheat (Triticum aestivum) growth. The slag material, which contains significant quantities of Mg and K, was applied to Mission (coarse‐silty, mixed, frigid Andic Fragiochrepts) and Palouse (fine‐silty, mixed, mesic Pachic Ultic Haploxerolls) silt loam soils at rates ranging from 0 to 40,000 kg/ha. Parameters evaluated included: (1) germination, (2) plant vigor, (3) yield, and (4) soil and plant tissue K, Ca and Mg.

Under field conditions slag application rates of 4,000 and 8,000 kg/ha reduced wheat stands and vigor; however, yields were not adversely affected when compared with the control. Application rates in excess of 8,000 kg/ha resulted in reduced germination, plant vigor, and yield and are consequently not recommended. Greenhouse studies provided further evidence to substantiate the field results.     

Effect of the substrate concentration and water activity on the yield and rate of the transfer reaction of β-galactosidase from Bacillus circulans

Prebiotic galactosyl oligosaccharides (GOS) are produced from lactose by the enzyme β-galactosidase. It is widely reported that the highest GOS levels are achieved when the initial lactose concentration is as high as possible; however, little evidence has been presented to explain this phenomenon. Using a system composed of the commercial β-galactosidase derived from Bacillus circulans known as Biolacta FN5, lactose and sucrose, the relative contribution of water activity, and substrate availability were assessed. Oligosaccharide levels did not appear to be affected by changes in water activity between 1.0 and 0.77 at a constant lactose concentration. The maximum oligosaccharide concentration increased at higher initial concentrations of lactose and sucrose, while initial reaction rates for transfer increased but remained constant for hydrolysis. This suggests that the high oligosaccharide levels achieved at the raised initial saccharide concentration are due to increases in reactions that form oligosaccharides rather than decreases in concurrent reactions, which degrade oligosaccharides. There were different effects from changing the initial concentration of lactose compared to sucrose, suggesting that the ability of lactose to act as a donor saccharide may be more important for increasing maximum oligosaccharide concentrations than the combined ability of both saccharides to act as galactosyl acceptors.     

Which species? What kind of diversity? Which ecosystem function? Some problems in studies of relations between biodiversity and ecosystem function

I examine a number of problems that need to be identified and accounted for when examining the relationships between diversity and ecosystem function. Among these are measures of diversity and complexity in ecosystems: species richness, diversity indices, functional groups, keystone species, connectance, etc, all of which may be difficult to relate to ecosystem function. Several important distinctions, when testing diversity–function relationships empirically, are discussed: Diversity of functional groups, diversity within functional groups vs. total diversity; manipulating variables such as body-size distributions vs. manipulating diversity per se; effects of diversity vs. effects of biomass; and diversity–function relations under stable vs. changing conditions or perturbations. It is argued that for the management and development of sustainable ecosystems, it is probably more important to understand the linkages between key species or functional groups and ecosystem function, rather than focusing on species diversity. This is because there are possible mechanistic relations between what species do in ecosystems and ecosystem function. Diversity, being an abstract and aggregated property of the species in the context of communities and ecosystems, lacks such direct relations to ecosystem functions.     

Interaction of curcumin and bixin with β-cyclodextrin: complexation methods, stability, and applications in food

This work aimed to compare methods for the formation of complexes of bixin and curcumin with β-cyclodextrin (β-CD) and to evaluate the stability of the complexes formed by these methods and their food applications. The stoichiometric relationship between curcumin and β-CD was 1:2 and that between bixin and β-CD was 1:1. Curcumin-β-CD and bixin-β-CD complexes formed by kneading, coprecipitation, and simple mixing were evaluated by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), or nuclear magnetic resonance (NMR-H). For both curcumin and bixin, the best method of complexation was coprecipitation. Complexation of colorants with β-CD promoted an intensification of color and increased water solubility; however, stabilization in the presence of light occurred only for bixin. Application of curcumin-β-CD in cheese and yogurt and bixin-β-CD in the curd did not alter the initial characteristics of the products, which were sensorialy well accepted. Therefore, the complexation of these natural colorants with β-CD favors their use in low-fat foods, broadening the field of industrial application.     

Fractionation of whey protein isolate with supercritical carbon dioxide to produce enriched α-lactalbumin and β-lactoglobulin food ingredients

An environmentally friendly protein fractionation process using supercritical carbon dioxide (SCO(2)) as an acid was developed to produce enriched α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) fractions from whey protein isolate solutions containing from 2 to 10% WPI. This study investigated the effects of pH, temperature, WPI concentration, and residence time on the precipitation kinetics and recovery yields of individual whey proteins and the relative enrichment and composition of both protein fractions. At 5.5-34 MPa and 60-65 °C, solubilized SCO(2) decreased solution pH and induced the formation and precipitation of α-LA aggregates. Gel electrophoresis and HPLC of the enriched fractions demonstrated the production of ≥ 60% pure α-LA, and ≥ 70% pure β-LG, under various operating conditions, from WPI containing ～57% β-LG and 21% α-LA. The enriched fractions are ready-to-use food ingredients with neutral pH, untainted by acids and contaminants.     

Effect of pH, NaCl, CaCl2 and temperature on self-assembly of β-lactoglobulin into nanofibrils: a central composite design study

The ability of certain globular proteins to self-assemble into amyloid-like fibrils in vitro opens opportunities for the development of new biomaterials with unique functional properties, like highly efficient gelation and viscosity enhancement. This work explored the individual and interacting effects of pH (1 to 3), NaCl (0-100 mM), CaCl(2) (0-80 mM) and heating temperature (80 to 120 °C) on the kinetics of β-lactoglobulin self-assembly and the morphology of resulting nanofibrils. Statistically significant (p < 0.05) interactions included CaCl(2)*temperature, NaCl*pH, CaCl(2)*pH, temperature*pH and NaCl*CaCl(2). Particularly notable was the very rapid self-assembly at pH 3 and the highly nonlinear effect of pH on self-assembly kinetics. Nanofibril morphologies ranged from long and semiflexible or curled and twisted to short and irregular. There did not seem to be a link between the kinetics of fibril formation and the morphology of fibrils, except at pH 3, where self-assembly was very rapid and fibrils were short and irregular, suggesting haphazard, uncontrolled self-assembly.     

Relationship between signaling and metabolic pathways of grapevines under temperature and light stresses—a review

Depending on plant genotype–environment interactions, cell signal transduction, and thereby gene expression, disruptive or promotive effects on grapevine physiology, metabolism, and, consequently, fruit quality and yield may occur. This review article aims to evaluate the effects of temperature and light stress on grapevine signaling and metabolic pathways to provide insights into breeding/engineering strategies for designing grapevines with improved quality, yield and tolerance. The modifications of signaling and metabolic pathways are discussed to assist geneticists with designing tolerant grape cultivars with high capacity of producing bioactive compounds and, thereby health-promoting effects in grapevines and humans.     

Relationship between the Agricultural Management of a Semi‐arid Soil and Microbiological Quality

Abstract

The establishment of the incidence of different agricultural management practices on soil microbiological quality has become an issue of wide concern. This study was aimed to (i) determine the effect of different agricultural management practices (ecological, integrated, conventional, and conventional with the addition of pig slurry) on the microbial activity of a semi‐arid soil at two different stages (cropped and fallow) and (ii) adapt an existing quantitative method to assess the microbiological soil quality in the different management systems. Several microbial and biochemical parameters, as well as two water‐soluble carbon (C) fractions, were measured in the soil samples. Significant differences (P<0.05) were found between the different agricultural management systems for most of the microbiological parameters during the cropped period. Factorial analysis indicated that adenosine triphosphate (ATP), microbial biomass C, diphenol oxidase activity, urease activity, and water‐soluble carbohydrates had a high weight in factor 1. These parameters were selected to form part of the equation for calculating a microbiological quality index. During the cropped period, the ecological management yielded the highest score of the microbial quality index, whereas, during the fallow period, no differences were found among the index scores of the different agricultural management systems.     

Initial stage of cheese production: a molecular modeling study of bovine and camel chymosin complexed with peptides from the chymosin-sensitive region of κ-casein

Bovine chymosin has long been the preferred enzyme used to coagulate cow's milk, in the initial stage of cheese production, during which it cleaves a specific bond in the milk protein κ-casein. Recently, camel chymosin has been shown to have a 70% higher clotting activity toward cow's milk and, moreover, to cleave κ-casein more selectively. Bovine chymosin, on the other hand, is a poor clotting agent toward camel's milk. This paper reports a molecular modeling study aimed at understanding this disparity, based on homology modeling and molecular dynamics simulations using peptide fragments of κ-casein from cow and camel in both bovine and camel chymosin. The results show that the complex between bovine chymosin and the fragment of camel κ-casein is indeed less stable in the binding pocket. The results also indicate that this in part may be due to charge repulsion between a lysine residue in bovine chymosin and an arginine residue in the P4 position of camel κ-casein.     

Matrix effects in analysis of β-agonists with LC-MS/MS: influence of analyte concentration, sample source, and SPE type

The synergistic influences of analyte concentration, sample source, and solid-phase extraction (SPE) type on matrix effects in the multiresidue analyses of eight β-agonists with LC-ESI-MS/MS were evaluated. Porcine muscle and liver extracts and urine from diverse sources were purified by strong or mixed-mode cation exchange and molecularly imprinted polymer SPE cartridges, respectively. Three spiked concentrations (2, 10, and 20 ng/mL) of eight β-agonists in the purified matrices and the different sample sources were analyzed. The results show that for most β-agonists there are significant differences in matrix effects between analyte concentrations or sample sources (P < 0.05), whereas there is no significant difference in matrix effects between different SPE cartridges (P > 0.05). Results from main effects testing indicated that analyte concentration was the main effector.