Improved heat stability by whey protein–surfactant interaction

One of the main changes that occur during heat treatment of milk is whey protein denaturation, which in its turn may lead to protein aggregation and gelation. In this contribution, the effect of lysophospholipids, the main components of lysolecithins, as well as alternative surfactants, on heat-induced whey protein aggregation has been studied. Hereby, attention was paid to the relation between polar lipid molecular structure (e.g. effect of alkyl chain length, effect of polar head group) and heat-stabilising properties. Residual protein determination in the supernatant obtained after centrifugation of heated whey protein solutions learned that whey protein aggregation was at least partly prevented in the presence of surfactants. As the short alkyl chain lysophospholipids were particularly effective heat stabilisers, hydrophilic surfactants seemed to be most effective, which may be ascribed to their higher critical aggregation concentration. Upon more severe heat treatment, protein aggregation was probed either in-situ by oscillatory rheology, or ex-situ by yield rheometry. As some surfactants significantly reduced the gel strength, or even prevented heat-induced gel formation, these experiments corroborated the heat-stabilising effect of hydrophilic surfactants. Nuclear Magnetic Resonance (NMR) enabled a more direct evaluation of the protein–surfactant interaction. A strong hydrophobic interaction between small molecular weight surfactants and whey proteins became obvious from the chemical shift of the surfactant hydrophobic groups in the NMR spectrum and could be quantified by pulsed field gradient NMR (pfg-NMR) diffusiometry. The results indicated that protein–surfactant interaction did not occur upon thermal denaturation, but already took place at room temperature. However, the effect of this interaction became mainly obvious during thermal treatment.     

Life cycle utility-informed maintenance planning based on lifetime functions: optimum balancing of cost,failure consequences and performance benefit

Decision-making regarding the optimum maintenance of civil infrastructure systems under uncertainty is a topic of paramount importance. This topic is experiencing growing interest within the field of life cycle structural engineering. Embedded within the decision-making process and optimum management of engineering systems is the structural performance evaluation, which is facilitated through a comprehensive life cycle risk assessment. Lifetime functions including survivor, availability, and hazard at component and system levels are utilised herein to model, using closed-form analytical expressions, the time-variant effect of intervention actions on the performance of civil infrastructure systems. The presented decision support framework based on lifetime functions has the ability to quantify maintenance cost, failure consequences and performance benefit in terms of utility by considering correlation effects. This framework effectively employs tri-objective optimisation procedures in order to determine optimum maintenance strategies under uncertainty. It provides optimum lifetime intervention plans allowing for utility-informed decision-making regarding maintenance of civil infrastructure systems. The effects of the risk attitude, correlation among components and the number of maintenance interventions on the optimum maintenance strategies are investigated. The capabilities of the proposed decision support framework are illustrated on five configurations of a four-component system and an existing highway bridge.     

HPLC–PDA/ESI–MS/MS detection of polymethoxylated flavones in highly degraded citrus juice: a quality control case study

Highly degraded citrus fruit juices collected during a quality control investigation of the Italian Ministry of Agricultural Alimentary and Forestry Policies (MIPAAF) were analyzed for verifying their technological history. The analyzed samples were fermented black fluids stated as degraded first strength juices, in order to justify communitarian aids. Polymethoxylated flavones (PMFs) detection of solid phase extracted (SPE) purified samples provided clean chromatograms and good separation of compounds of interest using high performance liquid chromatography coupled with diode array and mass spectrometry HPLC–PDA/ESI–MS/MS. Since the PMFs concentration is elevate in peel flavedo, it is directly correlated with juice extraction strength. Results showed that all analyzed samples presented a PMFs concentration ranging from two to eight times first strength juices, not respecting the minimum quality requirements of the European regulatory framework.     

LC/MS/MS detection of fungicide guazatine residues for quality assessment of commercial citrus fruit

An analytical protocol was developed for investigating guazatine occurrence in citrus fruit with the aim of controlling the import of treated fruits in countries where the use of this fungicide is forbidden. The main constituents of guazatine mixture (GN, GG, GNG, GGN, GGG, GGGN and GGGG) and the internal standard (dodine) were separated by high performance liquid chromatography using a hydrophilic end-capped Aquasil C₁₈ column and detected by ESI/MS/MS of parent ions, operating in positive mode. Extraction from citrus peels was performed with 1% HCOOH in water/acetone (1:2 v/v). The analytical method was statistically validated on three of the main constituents (GG, GGN and GGG) representing more than 65% of the total content. The regression lines, ranging from 0.100 to 3.750 mg/L of total guazatine, showed r ² > 0.990. Recoveries of about 81, 90 and 104% were obtained on average for the fortification level of 0.010, 0.035 and 0.060 mg/kg, respectively; the relative standard deviations ranged from 2 to 8% (n = 6). The limit of detection was below 0.0050 mg/kg, while the limit of quantification did not exceed 0.0065 mg/kg. The method was successfully applied to 77 samples of extra-European citrus fruit collected in the Italian market during the summer 2007. The results demonstrated that 64% of the investigated citrus samples contained guazatine over the residue limit value of 0.010 mg/kg for not allowed pesticides, evidencing the alarming illicit employ of this fungicide in citrus post-harvest treatments.     

Geothermal development in Nicaragua

In order to meet national energy requirements, Nicaragua has had to direct its attention towards sources of “alternative energy”, such as geothermal. Excellent geothermal prospects exist in this country, for which reason the Revolutionary Government has deemed it convenient to direct its energy policy towards this alternative source. Studies carried out during past years have led to the selection of nine areas in western Nicaragua, four of which were earmarked Very High Priority because they contain high enthalpy geothermal fields, three areas were earmarked High Priority and only two Low Priority. The positive results obtained in the Momotombo geothermal project have become an incentive to continue research and development nation-wide.At present, a power plant is operating with 35 MW at the Momotombo geothermal field; another 35 MW power plant is under construction in the same field; the El Hoyo-Monte Galan project is in the pre-feasibility phase and surveys are under way throughout national territory.     

PSpice modelling of ultrasound transducers: comparison of software models to experiment

This paper presents a complete PSpice model of an ultrasound single-element transducer, including electrical and mechanical matching as well as the focusing lens. By using this model, it is possible to obtain a relation between the electrical driving source and the acoustic velocity on the transducer surface. This boundary condition then allows the acoustic field to be calculated by numerical methods. Experimental data obtained with two different transducers are in good agreement with results predicted by the related models.     

Algorithm for identification of multivariable discrete-time linear systems

The method presented is for the z-transfer function matrix G(z) identification for constant-coefficient linear systems from samples of the impulse response matrix. By the proposed approach the roots of the minimal polynomial of G(z) and the corresponding residues are sequentially determined. The computational effort is here greatly reduced.     

Sensitivity analysis in power system dynamic stability studies

The stability limits for power systems can be defined by curves on the capability chart. In this paper the sensitivity of these curves versus system parameter perturbations is considered. The results also look interesting from a practical point of view, since a more realistic and efficient margin for stability can be defined. On this basis, the margin variations due to parameter perturbations are determined. Finally, a useful criterion is introduced to determine globally the influence of the parameter perturbations on the dynamic behaviour of the system.