Dynamical behavior of one-dimensional water molecule chains in zeolites: nanosecond time-scale molecular dynamics simulations of bikitaite

Nanosecond scale molecular dynamics simulations of the behavior of the one-dimensional water molecule chains adsorbed in the parallel nanochannels of bikitaite, a rare lithium containing zeolite, were performed at different temperatures and for the fully and partially hydrated material. New empirical potential functions have been developed for representing lithium–water interactions. The structure and the vibrational spectrum of bikitaite were in agreement both with experimental data and Car–Parrinello molecular dynamics results. Classical molecular dynamics simulations were extended to the nanosecond time scale in order to study the flip motion of water molecules around the hydrogen bonds connecting adjacent molecules in the chains, which has been observed by NMR experiments, and the dehydration mechanism at high temperature. Computed relaxation times of the flip motion follow the Arrhenius behavior found experimentally, but the activation energy of the simulated system is slightly underestimated. Based on the results of the simulations, it may be suggested that the dehydration proceeds by a defect-driven stepwise diffusion. The diffusive mechanism appears as a single-file motion: the molecules never pass one another, even at temperatures as high as about 1000 K, nor can they switch between different channels. However, the mean square displacement (MSD) of the molecules, computed with respect to the center of mass of the simulated system, shows an irregular trend from which the single-file diffusion cannot be clearly evidenced. If the MSDs are evaluated with respect to the center of mass of the molecules hosted in each channel, the expected dependence on the square root of time finally appears

Effects of additives and ingredient sizing on the shelf-life of "Amaretti" cookies

Cookies are characterised by moisture and water activity (aw) higher than 7% and 0.5, respectively. Cookies have the capacity of bending after baking, when they are fresh, unlike biscuits that break when bent. Hardening is the main cause of quality deterioration of cookies, which change from soft and pliable to firm and crumbly within a few days or even hours after baking. Little research has been done on cookies. "Amaretti" are typical Italian cookies, found in several regions of Italy. Freshly baked "Amaretti" are soft and delicious but undergo severe hardening after seven to ten days, thus limiting the shelf-life, so Amaretti can be marketed only locally. In the present work several attempts have been made in order to extend the shelf-life of Sardinian "Amaretti". In particular, changes to the formulation and to the almond particle size were made. The traditional formulation was, in fact, modified by adding rice starch (thickening agent) or mono-diglyceride of fatty acids (emulsifier). Almonds were grinded to a particle size lower or higher than 1 mm. Amaretti baked with the traditional recipe were used as control. After baking and cooling cookies were wrapped with an aluminium foil and stored at controlled temperature and humidity. Evolution of texture (as hardness) and aw during storage were followed instrumentally by a texture analyser and a hygrometer, respectively

Effectiveness of active and modified atmosphere packaging on the shelf-life extension of a cheese tart

The shelflife extension by MAP and AP of a typical cheese tart was studied. Baked tarts were packaged inside barrier to gas trays and wrapped with a barrier to gas and water film. Four batches were prepared: 1) Control; 2) MAP with different N2/CO2 ratios (70/30 and 20/80); 3) Trays with an iron oxide-based oxygen absorber. Tarts were stored at 20°C and sampled for analysis at 0,7, 14,27,35 and 48 days. Determinations inc1uded microbioIogical analyses (total bacterial count, moulds, yeast and staphylococci), chemical-physical parameters (pH, water activity and dry matter), gas changes (CO2, O2 and N2) inside MAP and AP trays, texture evolution and sensory analysis at our laboratories. AP allowed a shelf life of 48 days, MAP shelf lives were of 14 and 34 days for 70/30 and (20/80), respectiveIy, while controI tarts spoiled after only 7 days

Conservazione e sostenibilità: tecniche bioclimatiche tradizionali in ambito mediterraneo

Negli ultimi anni l’intero comparto edilizio è stato chiamato in causa in merito alla questione ambientale, poiché giudicato responsabile del 36% delle emissioni di gas serra e del 40% circa del consumo energetico totale in Europa. Il consumo inarrestabile dei suoli, la crescita indiscriminata dei centri urbani e l’utilizzo di materiali e tecniche energivori hanno condotto, come naturale conseguenza, a considerare il recupero del costruito come valida alternativa all’ulteriore utilizzo di suolo ed energia. Non sempre, però, le nuove tecnologie impiantistiche o di risanamento risultano compatibili con le peculiarità costruttive e distributive delle fabbriche storiche, nonché con i materiali da costruzione tradizionali. Sovente, poi, il conflitto esistente fra l’adeguamento alla normativa comunitaria relativa al contenimento dei consumi energetici e l’applicazione dei principi propri del restauro spinge il progettista a ricorrere alla deroga prospettata dalla normativa o a ricercare soluzioni “di comodo”, agendo quasi esclusivamente sugli impianti. Sappiamo bene, tuttavia, come nel corso degli ultimi decenni il ricorso alle tecnologie impiantistiche per il raggiungimento di standard di comfort sempre più elevati, abbia reso i consumi dovuti alla conduzione degli immobili (derivanti perlopiù da riscaldamento, raffrescamento e climatizzazione) particolarmente incidenti sull’intero bilancio energetico degli edifici. Questa particolare situazione risulta ancor più evidente nel caso di riuso di edifici tradizionali, generalmente sottoposti ad interventi di adeguamento alle necessità della vita contemporanea che portano a snaturare gli elementi costruttivi tipici e l’impianto distributivo della fabbrica originaria. Alcune peculiarità tecnologiche dell’architettura storica potrebbero, al contrario, rappresentare un modello a cui fare nuovamente riferimento, con l’apporto delle dovute integrazioni e correzioni indispensabili alla loro “attualizzazione”. È il caso, ad esempio, delle tecniche bioclimatiche preindustriali di riscaldamento, raffrescamento e ventilazione che, nel corso dei secoli, come testimoniato già ai tempi di Vitruvio, hanno consentito all'uomo di trarre giovamento, in termini di miglioramento del comfort abitativo, dall'adattamento (e sfruttamento) delle condizioni climatiche del luogo scelto per erigervi la propria dimora e che oggi, spesso, non vengono riconosciute o comprese, e per questo accantonate a favore delle nuove tecnologie. Sulla base di tali riflessioni, il presente lavoro intende mettere in evidenza le potenzialità di tali tecniche, con particolare riferimento a quelle diffuse nel bacino mediterraneo, nell’ottica di una vantaggiosa riscoperta e riproposizione delle stesse nell’ambito della riqualificazione energetica del costruito sottoposto a tutela, in affiancamento a dispositivi impiantistici con potenza e consumi conseguentemente ridotti

Behavior of water in the hydrophobic zeolite silicalite at different temperatures. A molecular dynamics study

Classical molecular dynamics simulations of water adsorbed in silicalite, a hydrophobic all-silica zeolite, were performed at different temperatures in the range 100-580 K, to explore possible phase transitions and to compare the behavior of adsorbed water with that of bulk water or water confined in nanopores of different geometry. We used a potential model including full flexibility both of water molecules and of the silicate framework. The results show an unexpected complexity. At very low temperatures (below 225 K), water appears to be mostly in form of amorphous solidlike clusters among which a slow molecule interchange occurs, giving rise to a single-file like diffusion on the time scale of our simulations. At intermediate temperatures, in the approximate range of 225-350 K, the behavior of water is almost liquidlike, whereas at higher temperatures, there are evidences of a vaporlike features, in agreement with the suggestions of previous theoretical and experimental works. This behavior is discussed by considering, among others, the average distribution of water in the channels, the size and lifetime of the hydrogen bonded clusters, and the water-water interaction energy. The results are compared with the available experimental data, previous simulations, and statistical mechanical studies

Molecular dynamics simulation of water confined in zeolites

Extended nanosecond scale MD simulations of water in bikitaite, silicalite and natrolite are illustrated. These systems are representative of different kinds of absorption of water in zeolites: hydrogen-bonded linear chains of water moleculars (bikitaite), water in hydrophobic materials (silicalite) and water molecules held in fixed ordered positions (natrolite). Results are in line with experimental results and with Car-Parrinello simulations, when available. The different microscopic behaviour of water in each considered zeolite is discussed

Rheological properties and baking quality of commercial durum wheat meals used to make flat crispy bread

Four commercial semolinas and four low-grade semolinas (LGS) samples were used in this study to make flat crispy bread (Carasau). The meals, doughs, and bread were compared with respect to a set of physical, chemical, and textural characteristics, and the bread evaluated by a trained sensory panel. LGSs had a higher extraction rate (higher ash content), finer granularity, and a higher damaged starch content than semolinas. The study revealed the key role of dry gluten content in determining hydration capacity of the dough, whereas damaged starch affected water absorption only in semolina samples. Gluten index and the ratio of gluten tenacity to extensibility (alveograph P/L) were significantly correlated with the weight of the dough discs following sheeting and molding. The panelists gave the highest quality score to the bread with the highest values of crackling and hardness. Textural and sensory attributes were both correlated with one another, and with gluten strength and tenacity, but not with the gluten content of the meal, which only affected final moisture content of the bread. Meal samples with a more tenacious and elastic gluten were more suited to produce flat crispy breads. The yellowness of durum wheat bread could not be predicted by measuring the color of the meal with a reflectance method