Solution calorimetry: A novel perspective into the dissolution process of food powders

The enthalpy of dissolution of two food powders, maltodextrin and skim milk, was studied by means of isothermal solution calorimetry. The effects of the moisture content and the physical state of the samples were investigated. A reduced exothermic response was found as the moisture content of the samples increased. It was shown that this effect is reversible upon re-drying of the solid, unless crystallization occurs. In the skim milk powder, crystallization of lactose occurred, leading to a less exothermic response. In addition, the dissolution kinetics of single particles was followed in situ with real time video acquisition and a novel image analysis technique. The data showed a significant effect of the physical state of the powder on the dissolution kinetics. Fully amorphous skim milk powder dissolved significantly faster than the recrystallized counterpart. A clear relation was observed between the physical state of the powders, their thermodynamic response and the dissolution kinetics.     

Polyelectrolyte screening effects on the dissolution of whey protein gels at high pH conditions

The literature reports an optimum NaOH concentration for the alkaline cleaning of whey deposits or gels; at NaOH concentrations higher than this optimum, cleaning proceeds much more slowly. Although this phenomenon is of great importance in the cleaning of dairy equipment, no conclusive physical explanation has yet been presented. In this study, we present strong evidence that the dissolution rate is affected by the equilibrium-swelling ratio in β-lactoglobulin (βLg) gels. The swelling ratio is greatly reduced in the presence of salts due to the polyelectrolyte screening effect of the cations. This has been observed in free-swelling βLg gels using gravimetrical analysis and in the uniaxial swelling of WPC gel deposits using fluid dynamic gauging. At high dissolution pH (>13.3), the high Na⁺ concentration reduces swelling in spite of the high surface charge of the protein. It is proposed that the reduction of the free volume inside the gel impedes the transport of the protein aggregates out of the NaOH penetration zone. We have also observed that the final dissolution rate of gels pre-soaked in 1 M NaOH or NaCl is similar, despite the difference in pH, and much lower than for untreated gels: the high Na⁺ concentration in the soaked gels hinders swelling, inhibiting the disentanglement of the protein clusters regardless of the high pH.     

Determination of killer activity in yeasts isolated from the elaboration of seasoned green table olives

In this work 51 yeasts strains isolated from seasoned green table olives and belonging to the Candida, Debaryomyces, Kluyveromyces, Pichia, and Saccharomyces genera were characterized by their killer activity in different conditions. Killer activity of isolates was analyzed in a medium with different pH's (3.5 to 8.5) and NaCl concentrations (5, 8, and 10%). At every pH tested, all the genera studied had killer strains, although the smallest percentages of killer yeasts were found at the highest pH (8.5). The presence of 5 and 8% NaCl increased the detected killer percentage, but the highest salt concentration (10%) decreased it. The interaction between the reference killer yeasts and yeasts isolated from olives was analyzed. Most isolates were killer-sensitive to one or more killer reference strains. Only 2 of the 51 strains tested were considered killer-neutral. Cross-reaction trials between isolates and spoilage yeasts showed that, of the isolates, nine killer strains, belonging to Debaryomyces hansenii, Kluyveromyces marxianus, Pichia anomala, Pichia guilliermondii, and Saccharomyces cerevisiae, had the broadest spectra of action against yeasts that cause spoilage. These killer yeasts and the toxins that they produce are candidates for further investigation as suppressors of indigenous olive table yeast growth. The results confirmed the highly polymorphic expression of the killing activity, with each strain showing different killer activities. This method may thus be very useful for simple and rapid characterization of yeast strains of industrial interest.     

Characterizing the migration of antioxidants from polypropylene into fatty food simulants

The migration (diffusion and equilibrium) processes of antioxidants (AOs) from polypropylene (PP) films of different thicknesses into n-heptane and 95% ethanol as fatty food simulants were analysed at 20, 37 and 60°C. Heptane fully extracted the AOs from the polymer while a partition equilibrium described the migration to ethanol. The kinetics of migration were also studied via the diffusion coefficients. As expected, diffusion was found to be faster when the polymer was in contact with heptane, due to polymer swelling by the solvent. The kinetics of the process in ethanol was described by different theoretical expressions which are discussed. Equations disregarding partition equilibrium failed to describe the process and the diffusion coefficient values obtained through them were much smaller than the actual ones and dependent on film thickness. The results also showed the significance of food simulant selection in the analysis of food-packaging interactions and migration variability with thickness.     

New tools to assess toxicity, bioaccessibility and uptake of chemical contaminants in meat and seafood

Meat and seafood chemical contaminants can be very dangerous for human health. The way in which food chemical contaminants are currently controlled is not optimal as the food cooking, processing and eating habits are generally not considered by authorities. The current review discusses the available information related to the toxicity of the most relevant meat and seafood chemical contaminants, their bioaccessibility after cooking or processing, and the implications for human health. In addition, the current in vivo toxicity and alternative tests carried out for testing the effects of food chemical contaminants are illustrated, as well as new detection tools. The use of non-carcinogenic functional cell models, of alternative animal models like zebrafish embryos, and a toxicogenomic approach seem to be the most promising strategy for the toxicity assessment of food chemical contaminants.     

Swiss pumped hydro storage potential for Germany’s electricity system under high penetration of intermittent renewable energy

In order to cut greenhouse-gas emissions and increase energy security,the European Commission stimulates the deployment of intermittent renewable energy sources（IRES） towards 2050.In an electricity system with high shares of IRES implemented in the network,energy balancing like storage is needed to secure grid stability and smooth demand satisfaction.Pumped hydro storage（PHS） is at this moment the best option for large scale storage.Switzerland has strong ambitions to further develop their PHS sector and become the battery of Europe.In this research,the potential of the Swiss PSH plants is explored,whilst taking inflow into the upper reservoirs of the PHS plants into consideration.To simulate electricity imbalance,Germany is used as a case study.Germany already has a high penetration of IRES and has plans to increase installed IRES capacity.By using an energy planning model（Power Plan）,three future scenarios of the German electricity system were designed,each with a different set of IRES installed（solar,mixed and wind）.Results show that the Swiss battery ambition offers most benefits to a wind-oriented scenario,reducing both shortages as well as surpluses.Water inflow in Swiss PHS-reservoirs is of minor importance when looking at security of supply,although it was shown that the solarscenario profits more from inflow in terms of system stability.However,a potential conflict was observed in the solar-scenario between the need for electricity storage and the storage of natural inflow,resulting in more surpluses in the system when inflow was taken into account.     

Optimal Design of Hybrid Microgrid in Isolated Communities of Ecuador

In rural territories, the communities use energy sources based on fossil fuels to supply themselves with electricity, which may address two main problems: greenhouse gas emissions and high fuel prices. Hence, there is an opportunity to include renewable resources in the energy mix. This paper develops an optimization model to determine the optimal sizing, the total annual investment cost in renewable generation, and other operating costs of the components of a hybrid microgrid. By running a k-means clustering algorithm on a meteorological dataset of the community under study, the hourly representative values become input parameters in the proposed optimization model. The method for the optimal design of hybrid microgrid is analyzed in six operating scenarios considering:（1） 24-hour continuous power supply;（2） load shedding percentage;（3） diesel power generator（genset） curtailment;（4） the worst meteorological conditions;（5） the use of renewable energy sources including battery energy storage systems（BESSs）; and（6） the use of genset. A mathematical programming language（AMPL） tool is used to find solutions of the proposed optimization model. Results show that the total costs of microgrid in the scenarios that cover 100% of the load demand（without considering the scenario with 100% renewables） increase by over 16% compared with the scenario with genset operation limitation. For the designs with power supply restrictions, the total cost of microgrid in the scenario with load shedding is reduced by over 27% compared with that without load shedding.     

Supramolecular spin valves

Magnetic molecules are potential building blocks for the design of spintronic devices. Moreover, molecular materials enable the combination of bottom-up processing techniques, for example with conventional top-down nanofabrication. The development of solid-state spintronic devices based on the giant magnetoresistance, tunnel magnetoresistance and spin-valve effects has revolutionized magnetic memory applications. Recently, a significant improvement of the spin-relaxation time has been observed in organic semiconductor tunnel junctions, single non-magnetic molecules coupled to magnetic electrodes have shown giant magnetoresistance and hybrid devices exploiting the quantum tunnelling properties of single-molecule magnets have been proposed. Herein, we present an original spin-valve device in which a non-magnetic molecular quantum dot, made of a single-walled carbon nanotube contacted with non-magnetic electrodes, is laterally coupled through supramolecular interactions to TbPc(2) single-molecule magnets (Pc=phthalocyanine). Their localized magnetic moments lead to a magnetic field dependence of the electrical transport through the single-walled carbon nanotube, resulting in magnetoresistance ratios up to 300% at temperatures less than 1 K. We thus demonstrate the functionality of a supramolecular spin valve without magnetic leads. Our results open up prospects of new spintronic devices with quantum properties.