Emma S. Sánchez

Compositional features of polysaccharides from Aloe vera (Aloe barbadensis Miller) plant tissues

A complete chemical characterisation of Aloe vera plant (Aloe barbadensis Miller) was carried out from the dissection of the plant whole leaves in filets and skin. In addition, a mucilaginous gel extracted from the filets was also characterised. Extraction with ethanol of lyophilised Aloe fractions (AIRs) allowed to concentrate the major fraction composed of carbohydrates up to 80%. The composition of the main type of polysaccharides present in the Aloe AIRs was determined. Mannose and cellulosic glucose were the major polysaccharide components in all AIRs, significant amounts of pectic polysaccharides were also detected. Sequential extraction of polysaccharides present in Aloe vera plant portions, revealed that two main types of mannose-containing polymers were present in the Aloe vera plant. The polysaccharide detected in the filet and in the gel fractions corresponded to a storage polysaccharide located within the protoplast of the parenchymatous cells. Its structural and compositional features corresponded to the active polysaccharide known as acemannan. On the contrary, in the skin tissue, the mannosyl residues arose from a structural polysaccharide located within the cell wall matrix. Structural and compositional differences between both polymers were confirmed by methylation analysis. The fact that acemannan is a reserve polysaccharide might help to explain most of the compositional variations reported in the literature for Aloe vera carbohydrates. Further, sequential extraction allowed us to identify several pectic polysaccharides, rich in uronic acids, with a composition similar to that of several antitumoral polymers found in different plant tissues.

Use of ultrasound to increase mass transport rates during osmotic dehydration

Experiments on osmotic dehydration of 1 cm apple cubes in 70 °Brix sucrose solution using ultrasound treatment were carried out at 40, 50, 60 and 70 °C. Acoustic pressure and frequency was measured to characterize the ultrasonic bath. Mass transfer was described by Ficks unsteady state diffusion equation. An important influence of the solution temperature on water transport was obtained. Measured water diffusivity coefficients (Dw) ranged from 2.6 × 1010−10 m2 s−1 at 40 °C to 6.8 × 10−10 m2 s−1 at 70 °C. Similar sucrose gain was measured at different temperatures, with an average effective sucrose diffusivity coefficient (Ds) (7.9 ± 0.2) × 10−11 m2 s−1. Similar experiments were performed under dynamic agitation conditions. A significant decrease in water and solute transport rates was detected when agitation was applied instead of sonication.

Water and salt diffusion during cheese ripening: effect of the external and internal resistances to mass transfer

Abstract High humidities of drying medium lead to lower drying rates, and both external or internal conditions determine the drying rate. Thus, a diffusional model has been developed assuming that the external resistance to mass transfer could not be neglected in these cases and solved by a finite difference method. The external mass transfer coefficient was estimated from the literature. This mathematical model was used to identify water and salt effective diffusivity coefficients by using experimental data of ripening experiments carried out on parallelepipedal Mahon cheeses of 0.14 m ×0.14 m ×0.09 m edges kept at 12°C and 85% RH. Using these identified values, 7.8×10 −12 m 2 / s for moisture diffusion and 5.3×10 −10 m 2 / s for salt diffusion, average moisture content and water and salt profiles during the ripening of 0.20 m ×0.20 m ×0.10 m cheeses ripened at 12°C and two different relative humidities, 70% and 80% RH, were accurately simulated.

Calorimetric Techniques Applied to the Determination of Isosteric Heat of Desorption for Potato

Temperature had an influence on desorption isotherms of potato measured at six different temperatures (4, 14, 21, 28, 35 and 50°C). The parameters of the Oswin, Henderson, Halsey and GAB models, for isotherm representation, were identified. Water activity at any temperature could be calculated by means of only one equation using the GAB model, which gave the best fit to experimental data in all the range of water activity studied (0·4–0·9). Isosteric heats of water desorption of potato, were determined from the desorption isotherms following the Clausius–Clapeyron equation and from two thermal analysis techniques (DSC and TG). Similar results were obtained through the two methods, indicating that calorimetric techniques are adequate to obtain the isosteric heat of desorption of products with a high starch content.

Developmental and ripening-related effects on the cell wall of apricot (Prunus armeniaca) fruit

Alcohol-insoluble residues (AIRs) were prepared from apricots at six stages during development/ripening on the tree. To investigate the changes in cell wall polymers, and in particular those affecting pectic polysaccharides, the AIR preparations were sequentially extracted with water, cyclohexane-trans-1,2-diamine-N,N,N′,N′-tetraacetate (CDTA) and Na2CO3. A significant proportion of initially Na2CO3-soluble pectic polysaccharides became water- and CDTA-soluble during the ripening process. In terms of composition, a significant decrease in galactose and uronic acid content was detected in all the extractions, whereas the percentage of arabinose increased in both water and CDTA-soluble polymers but decreased in the Na2CO3-extracted polysaccharides. The ability of pectic polysaccharides to cross-link was diminished during ripening due to an overall increase in the concentration of Na+ or K+ associated with the AIRs. This was accompanied by a decrease in the amounts of Ca2+ and Mg2+. The decrease in pectic galactans and the inhibition of pectin cross-linking detected within the pectic backbone are probably linked to the softening process observed during apricot ripening.

Effect of temperature and gas composition on the shelf-life of dehydrated apricots / Efecto de la temperatura y composición de la atmósfera sobre la vida útil de albaricoques deshidratados

Dehydrated apricots were stored under different conditions of temperature (14, 21, 28 and 35 °C), gas composition (100% CO2, 80% N2-20%CO2 and air) and packaging material (glass and film with an oxygen transmission rate of 14.39 ± 0.88 mL/m2/day). The most representative physical and chemi cal characteristics (L*, a*, b*, texture, water activity, sugars, moisture and SO, contents) regarding the shelf-life of dehydrated apricots were evaluated during storage. Storage temperature showed a sig nificant influence on L*, sucrose content ( p > 99%), b* (p > 95%) and SO, content (p > 99.9%). The rate of decrease of SO, content and L* was well described by a first order kinetic. The influence of gas composition was important to both L* and a* (p > 95%) and SO, content (p > 99.9%). Principal compo nent analysis showed that the first two components accounted for 100% of the total variance. The first principal component which included L*, a*, b* and SO, content accounted for 75.3% of the vari ance. Sucrose, fructose and glucose contents were chiefly involved in the second principal compo nent.