Search results for "Water content"
showing 10 items of 380 documents
Is the formation of a zeolite from a dry powder via a gas phase transport process possible?
1994
Abstract ZSM-5 was synthesized by four methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in the form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO2·A2O3 gels at 650°C were transformed into zeolites in the presence of dried NH4F and TPABr. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure under the given reaction conditions. To explain the formation of a zeolite, we suggest a vapor phase mass transfer process with SiF4 as the mobile species between the solid phase, which contains the amorphous Si/Al pre…
A combined optical-microwave method to retrieve soil moisture over vegetated areas
2011
A simple approach for correcting for the effect of vegetation in the estimation of the surface soil moisture (wS) from L-band passive microwave observations is presented in this study. The approach is based on semi-empirical relationships between soil moisture and the polarized reflectivity including the effect of the vegetation optical depth which is parameterized as a function of the normalized vegetation difference index (NDVI). The method was tested against in situ measurements collected over a grass site from 2004 to 2007 (SMOSREX experiment). Two polarizations (horizontal/vertical) and five incidence angles (20◦, 30◦, 40◦, 50◦, and 60◦) were considered in the analysis. The best wS est…
A novel alpha-amylase-lipase formulation as anti-staling agent in durum wheat bread
2016
The aim of this work has been to evaluate the anti-staling effect exerted by a novel α-amylase-lipase enzyme formulation on durum wheat bread, in comparison with four different commercial amylase preparations and with control without added enzymes. Bread-making trials were carried out at industrial level. Sliced bread, packed under modified atmosphere, was analyzed for texture profile, moisture content, and water activity during 90 days. Crumb sections were submitted to environmental scanning electron microscopy at the end of the storage period. The α-amylase-lipase enzyme preparation showed synergistic interactions in preventing staling. In particular, bread added of these two enzymes in m…
The role of water in the impact of high pressure on the myrosinase activity and glucosinolate content in seedlings from Brussels sprouts
2019
Abstract In this study, it was shown that the amount of available water was found to influence the high pressure processing (HPP) effect on both myrosinase activity and total glucosinolate concentration in Brussels sprouts seedlings. Brussels sprouts seedlings with different water content (wc = 4.8–89.4%) and water activity (aw = 0.17–0.97) were pressurized at selected pressures between 200 and 800 MPa (5 °C and 3 min), thereby affecting pressure-induced enzyme denaturation, molecular diffusion, and cell permeability differently. The myrosinase activity and intact glucosinolate content in the dry seedlings (wc Industrial relevance High pressure processing (HPP) is increasingly applied in t…
Moisture loss, gain and migration in foods and its impact on food quality
2010
Abstract: Moisture loss, gain and transfer, whether originating from exchanges with the atmosphere or with another component of the food, always cause deterioration in the overall quality of the food through softening, toughening, breakdown, and swelling or shrinkage caused by phase transitions or dissolution (Petersen et al., 1999). In most cases, water migrations lead to a deterioration of the overall quality (organoleptic or hygienic) of the food. With a view to better understanding physical deterioration of food and to provide a tool to better control food quality (and give a longer shelf life) this chapter reviews the water relationships in foods with a particular focus on glass-transi…
Water in Dairy Products | Analysis and Measurement of Water Activity
2011
Water activity of a system (aw) is a thermodynamic concept used to characterize the contained water. It has been considered, in spite of some limitations, as the most important parameter in food technology for the past 50 years. It can be measured by the ratio (p/p0) of the water vapor pressure in the atmosphere at equilibrium with the material to the saturated vapor pressure of pure water at the same temperature, or by the physical properties related to it (freezing point depression, mechanical/electrical properties). Although the physical/chemical mechanisms responsible for the depression of aw as compared to that of pure water are more or less identified, the expressions describing the r…
How and why does willow biochar increase a clay soil water retention capacity?
2018
Addition of biochar into a soil changes its water retention properties by modifying soil textural and structural properties. In addition, internal micrometer-scale porosity that is able to directly store readily plant available water affects soil water retention properties. This study shows how precise knowledge of the internal micrometer-scale pore size distribution of biochar can deepen the understanding of the biochar-water interactions in soils. The micrometer-scale porosity of willow biochar was quantitatively and qualitatively characterized using X-ray tomography, 3D image analysis and Helium ion microscopy. The effect of biochar application on clay soil water retention was studied by…
Critical analysis of thermal inertia approaches for surface soil water content retrieval
2013
The “thermal inertia” method to retrieve surface soil water content maps on bare or sparsely-vegetated soils is analysed. The study area is a small experimental watershed, where optical and thermal images (in day and night time) and in situ data were simultaneously acquired. The sensitivity of thermal inertia to the phase difference between incoming radiation and soil temperature is demonstrated. Thus, to obtain an accurate value of the phase difference, the temporal distance between thermographs using a three-temperature approach is evaluated. We highlight when a cosine correction of the temperature needs to be applied, depending on whether the thermal inertia formulation includes two gene…
Seasonal changes of the infiltration rates in a Mediterranean scrubland on limestone
1997
To investigate the seasonal changes of infiltration rates, measurements by means of simulated rainfall experiments and cylinder infiltrometer were done in a small E–W oriented watershed in Southeast Spain. Data were collected during both the wet seasons (autumn, winter and spring) and the dry season (summer). Infiltration rates were very high in summer, when direct surface runoff is very low. During the wet seasons, the infiltration rates were lower due to the increase in soil moisture. Measurements by means of both ponding as well as simulated rainfall are suitable to study the infiltration process. The former needs more replications, due to the small observation area encompassed for each …
Sampling procedure in a willow plantation for estimation of moisture content
2015
Abstract Heating value and fuel quality of wood is closely connected to moisture content. In this work the variation of moisture content (MC) of short rotation coppice (SRC) willow shoots is described for five clones during one harvesting season. Subsequently an appropriate sampling procedure minimising labour costs and sampling uncertainty is proposed, where the MC of a single stem section with the length of 10–50 cm corresponds to the mean shoot moisture content (MSMC) with a bias of maximum 11 g kg −1 . This bias can be reduced by selecting the stem section according to the particular clone. The average difference in MSMC between the largest and smallest shoot in a stump was 31 g kg −1 .…