Analytical strategies for the determination of biogenic amines in dairy products

Biogenic amines (BA) are mainly produced by the decarboxylation of amino acids by enzymes from microorganisms that emerge during food fermentation or due to incorrectly applied preservation processes. The presence of these compounds in food can lead to a series of negative effects on human health. To prevent the ingestion of high amounts of BA, their concentration in certain foods needs to be controlled. Although maximum legal levels have not yet been established for dairy products, potential adverse effects have given rise to a substantial number of analytical and microbiological studies: they report concentrations ranging from a few mg/kg to several g/kg. This article provides an overview of the analytical methods for the determination of biogenic amines in dairy products, with particular focus on the most recent and/or most promising advances in this field. We not only provide a summary of analytical techniques but also list the required sample pretreatments. Since high performance liquid chromatography with derivatization is the most widely used method, we describe it in greater detail, including a comparison of derivatizing agents. Further alternative techniques for the determination of BA are likewise described. The use of biosensors for BA in dairy products is emerging, and current results are promising; this paper thus also features a section on the subject. This review can serve as a helpful guideline for choosing the best option to determine BA in dairy products, especially for beginners in the field.     

Deflections in sawn timber beams with stochastic properties

A stochastic model is proposed to study the behavior of structural sawn beams of Argentinean Eucalyptus grandis with the aim of improving the predictability of the elastic deformations. The enhancement of the mid-span deflection calculation is based on a probabilistic model of the Modulus of Elasticity (MOE) and the representation of its lengthwise variability through a random field. The standard model that uses a MOE variable assumed random from piece to piece but deterministic (constant) within each piece is obtained as a particular case. In order to obtain a statistical representation of the MOE, the Principle of Maximum Entropy (PME) is employed. Experimental data obtained from bending tests are employed to find the parameters of the derived Probability Density Function (PDF). The PDF of the mid-span deformations is numerically obtained through the Stochastic Finite Element Method (SFEM) and Monte Carlo Simulations (MCS). Numerical results are validated with experimental values. Deflections of structural sized beams under usual loads are obtained. Finally, the stochastic model is used to compare with the serviceability requirements established in the Argentinean design code. It is shown that the structural performance of timber beams is found through a more realistic material approach.     

An easy parameter estimation procedure for modeling a HT-PEMFC

Fuel cells are a very complex system in which many phenomena of different nature occur simultaneously and within a small space, so a truthful measurement of some variables is not feasible using state-of-the-art technology. If a deep knowledge of the unit is desired, modeling can be of great help when it is properly used as it is possible to calculate the value of the variables of interest by adjusting experimental data. However, when models are complicated, it is not trivial to identify in which way a certain parameter alters the model results and then it is necessary to resort to sensitivity analysis before approaching an adequate parameter estimation procedure. In this work, a parameter estimation procedure has been proposed with the results obtained from the sensitivity analysis applied to a high temperature proton exchange membrane fuel cell (HT-PEMFC) model. The procedure has been demonstrated to be straightforwardly applicable as well as effective, which makes it suitable to be used as engineering tool to obtain a first consistent value of the parameters that define the main characteristics of a HT-PEMFC.     

Numerical validation of a finite element thin‐walled beam model of a composite wind turbine blade

This paper presents a numerical validation of a thin‐walled beam (TWB) finite element (FE) model of a realistic wind turbine rotor blade. Based on the theory originally developed by Librescu et al. and later extended to suit FE modelling by Phuong, Lee and others, this computationally efficient yet accurate numerical model is capable of capturing most of the features found in large blades including thin‐walled hollow cross section with variable thickness along the section's contour, inner reinforcements, arbitrary material layup and non‐linear anisotropic fibre‐reinforced composites; the present application is, for the time being, restricted to linearity. This one‐dimensional (1D) FE model allows retaining information of different regions of the blade's shell and therefore approximates the behaviour of more complex three‐dimensional (3D) shell or solid FE models more accurately than typical 1D FE beam models. A 9.2 m rotor blade, previously reported in specialized literature, was chosen as a case study to validate the static and dynamic behaviour predicted by a TWB model against an industry‐standard 3D shell model built in a commercial software tool. Given the geometric and material complexities involved, an excellent agreement was found for static deformation curves, as well as a good prediction of the lowest frequency modes in terms of resonance frequencies, mode shapes and frequency response functions; the highest (sixth) frequency mode shows only a fair agreement as expected for an FE model. It is concluded that despite its simplicity, a TWB FE model is sufficiently accurate to serve as a design tool for the recursive analyses required during design and optimization stages of wind turbines using only readily available computational tools. Copyright © 2011 John Wiley & Sons, Ltd.     

The use of floral characters in <Emphasis Type="Italic">Capparis</Emphasis> sect. <Emphasis Type="Italic">Capparis</Emphasis> to determine the botanical and geographical origin of capers

Capers of commerce are flower buds of Capparis species, most of them presumably of the species C. spinosa and they are considered as such in international food legislation. However, in the Mediterranean countries of Europe, Asia, and North Africa, that are the main producers of capers, four different species have been detected in the commercial product: C. spinosa, C. sicula, C. orientalis and C. aegyptia. In this paper the study of morphological characters, easily detectable under optical microscope (number of stamens, anther shape, and morphology of nectary) has proven to be a simple and cheap technique to recognize the presence of the above-mentioned species in commercial capers and the relative percentages of each, this being a good indicator of the most likely geographical origin.     

Statistical analysis of weather conditions based on the Clearness Index and correlation with meteorological variables

The Clearness Index and the ratio between diffuse and global irradiance for different time scales are used to define a taxonomy for sky conditions and to study patterns to provide information for production-oriented probabilistic risk analysis studies for utility-level PV arrays. The study is focused on the definition of probabilities and distribution functions for the defined taxonomy of sky conditions. Correlations of the Clearness Index are investigated with different meteorological variables, to finally highlight that the only important correlation besides the irradiance is given by the relative humidity, though with a negative pattern. In conclusion, the analysis has shown that the three constraints of the standard test conditions (1000 W/m², 25 °C, air mass of 1.5 global) normally applied for laboratory characterisation of PV modules are actually never simultaneously met outdoor.     

Improving the phytochemical composition of broccoli sprouts by elicitation

In order to increase the concentrations of bioactive compounds in broccoli sprouts, exogenous elicitors: methionine, tryptophan, chitosan, salicylic acid (SA) and methyl jasmonate (MeJA) were sprayed at different concentrations during germination. The effects of the elicitors on vitamin C, phenolic compounds and glucosinolate levels were assessed in 3, 5 and 7-days old seedlings. The application of 200, 300 μM SA and 0.01% chitosan induced increases, by 26%, 18% and 54%, respectively in the content of vitamin C in 5 days old broccoli sprouts. Flavonoid concentration was also increased by 31% and 33% after 10 μM MeJA and 100 μM SA treatments, respectively in 7 days old broccoli sprouts. In contrast, methionine or tryptophan solutions did not positively affect the vitamin C or the phenolic compounds in the sprouts. The individual classes of glucosinolates respond differently to the elicitor treatment. Methionine, a sulphur-containing amino acid, applied at 5 mM, significantly increased, by 32%, the levels of aliphatic glucosinolates. However, indole glucosinolates presented a significant response to the induction with tryptophan, SA or MeJA treatments. Tryptophan at 10 mM concentration augmented by 1.8-fold the indole glucosinolate concentration in 7 days old broccoli sprouts, and the treatments of 100 μM SA and 25 μM MeJA also induced significantly higher amounts of indole glucosinolates (by 33% and 51%, respectively) in 7 days old treated broccoli sprouts. Therefore, the application of elicitors could be a useful tool for improving the bioactive metabolites in broccoli sprouts for fresh consumption or functional ingredients for nutraceuticals foods.     

GATA-like protein-1 (GLP-1) is required for normal germ cell development during embryonic oogenesis

Oogenesis and primordial follicle formation are tightly linked processes, requiring organized and precisely timed communication between somatic and germ cells. Deviations in ovarian cell cross talk, or aberrant gene expression within one of the cell populations, can lead to follicle loss or dysfunction, resulting in infertility. Expression of GATA-like protein-1 (GLP-1) in ovarian somatic cells is required for normal fertility in female mice, as GLP-1 deficiency leads to the absence of oocytes at birth. However, the timing and nature of this germ cell loss is not well understood. In this study, we characterize the embryonic germ cell loss in GLP-1 null mice. Quantitative PCR demonstrates that ovarian Glp-1 mRNA is expressed in a bimodal pattern during embryogenesis, peaking at E13.5-14.5 and again at birth. In contrast, adult ovaries express low but detectable levels of Glp-1 mRNA. Analysis of developing GLP-1 null mouse ovaries shows that germ cells are appropriately specified and migrate normally to nascent gonads. Upon arrival at the gonad, precocious loss of germ cells begins at around E13.5. This loss is completed by birth and is accompanied by defects in the expression of genes associated with meiotic entry. Interestingly, somatic pregranulosa cells still form basement membranes surrounding germ line cysts and express mRNA encoding paracrine signaling molecules that communicate with oocytes, albeit at lower levels than normal. Together, these data imply that the somatic cell protein GLP-1 is not necessary for many pregranulosa cell functions but is required for germ cell survival.