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The aim of this work was to analyse the effect of pectin and glycerol concentration on colour, mechanical properties and water vapour permeability of pectin edible films. Pectin films were obtained from apple pectin film-forming solutions at concentrations of 1.5, 2.5 and 3.5%. Glycerol was added as a plasticizer at 30, 50 and 70% (w/w of pectin). Colour was measured in the L*a*b* system and total colour difference was calculated. Water vapour permeability at relative humidity differentials of 30-100% was measured at 25°C. Mechanical properties were presented as tensile force and elongation at break. Based on the results obtained, increasing content of pectin caused an increase in total colour difference, water vapour permeability and tensile force of ana-lysed films. Glycerol caused increasing elongation at break and water vapour permeability.
Water vapour sorption processes on mixtures of soil and organic fertiliser Rosahumus (RH) were investigated. Mixtures were prepared with Orthic Luvisol soil formed from loamy sand and Haplic Luvisol soil formed from loess. Samples contained different doses of fertiliser in the range from 1 to 50 weight percent. Differences in water vapour sorption on Rosahumus (RH) as well as the soils were observed. The properties of soil mixtures and organic material depended on the properties of both components and on the dose of Rosahumus. However, fertiliser was a dominant factor in sorption processes of investigated mixtures. Adsorption isotherms obtained by gravimetric method belonged to the same type II, in accordance to the BET classification. Significantly higher influence on the water vapour sorption was associated with fertiliser dose and was greater for mixtures with soil formed from loess. The increase of water vapour sorption was visibly higher for mixtures below 4% of Rosahumus content. On the other hand, greater concentration of RH resulted in similar amount of water vapour sorption and for Rosahumus dose of 50% the sorption was practically the same. Similar results were found for the maximum hygroscopicity (Mh) of mixtures. Strong correlation was observed between the Mh and the amount of added organic fertiliser with determination coefficient (R2) from 0.997 to 0.998.
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The study was aimed at investigating caking of sweet whey powder and whey demineralized as a result of water vapor adsorption in respect of their sorption capacity. The analysis of the course of kinetic curves demonstrated that sweet whey was characterised by a higher capacity and rate of water vapour adsorption as compared to the demineralized whey. During storage at relative humidity of RH>0.43 the powders were subject to caking once the material reached water activity (aw) of 0.3-0.4, yet the sticking of powder particles proceeded faster in the case of sweet whey.
Sorption properties of some ingredients of muesli such as flakes and dried and candied fruits were investigated in this work. Kinetics of water vapor sorption at water activity of 1.00, 0,755, 0.239 and 0.00 was continuously measured. Kinetics of water sorption was well described by the solution of the Second Fick’s Law. However, the superficial values of equilibrium water content were obtained by kinetic measurements. The shape factor in the Fick’s equation was dependent on water activity. It was shown that in the analysed products adsorption process goes faster than the desorption one. Hence desorption of water from fruits and adsorption by flakes seems to be a limiting factor for water transfer in mixtures consisting of cereals and fruits.
Rye plants were grown in a nutrient solution prepa- red according to Hoagland for 2 weeks at pH 7, next for 14 days at pH 4.5 (without Cu+2) and in the presence of 20, 50, or 100 mg dm-3 copper ions. The control plants were grown continuously at pH 7. The physicochemical surface properties of the roots were exa- mined using two adsorbates – polar (water vapour) and non-polar (nitrogen). The surface properties of the roots grown at pH 4.5 without Cu+2 were apparently the same as those of controls. The roots of rye which grew in the presence of Cu+2 were characte- rized by lower (relative to controls) specific surface area values. Statistically significant differences in the size of the apparent surface area (determined by water vapour) were reported for roots in- cubated with copper ions at a concentration of 20 and 50 mg dm-3. The average water vapour adsorption energy of the root surface decreased under the stress conditions. There were no statistically significant differences for the free surface area and characteristic energy of nitrogen adsorption.
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