Carmen Rosselló

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.

DRYING OF CARROTS. I. DRYING MODELS.

ABSTRACT Three models of different complexity are proposed to describe the falling rate period of the carrot drying process with shrinkage. A moving or fixed boundary problem as well as a constant or local moisture and temperature dependent effective diffusivity are considered. The moving boundary problem is solved by an explicit finite difference method. Heat transfer coefficient and effective diffusivity identification were carried out. The results of the heat transfer coefficient show a good agreement with other sources. Using experimental data and the models. describing the heat and mass transfer three different expressions for the effective diffusivity are established. Two of them are only temperature dependent considering or not particle shrinkage. The third one takes into account temperature and local moisture as well as shrinkage. Drying of foods is a complicated process involving simultaneous coupled heat and mass transfer phenomena which occur inside the material being dried (Chiang and Petersen...

Drying models for green peas

Abstract A fixed or moving boundary problem was considered for the drying of green peas. The first model was solved by separation of variables, assuming that sample size and geometry remain constant during the process. For the second model, a finite difference method was used. Using experimental data from experiments carried out at different air-drying temperatures (40, 60 and 80 °C), two different expressions, of Arrhenius type, for the effective diffusivity dependence on the air temperature were obtained. Throughout these expressions, it was possible to simulate the drying kinetics of green peas at temperatures (50, 70 and 90 °C) different from those used to obtain the models. The second model was found to be more precise (percentage of explained variance > 99.8%) than the first one (>98.4%).

Effects of addition of carrot dietary fibre on the ripening process of a dry fermented sausage (sobrassada).

Four formulations of a dry fermented sausage, known as sobrassada, containing different percentages of carrot dietary fibre (DF) [3% (S3), 6% (S6), 9% (S9) and 12% (S12) (w/w)] were analyzed for various physico-chemical and microbiological parameters and sensory attributes. The ripening process was monitored throughout storage. The pH of DF-supplemented sobrassadas was critically affected during ripening by the amount of DF incorporated, the values for sobrassada samples containing over 3% of DF suggested that the fermentation process in these samples was not successful. In addition, textural parameters, such as hardness and compression work, were significantly affected by the addition of over 3% of DF. The lipolytic process, one of the major biochemical events, was only affected when relatively large percentages of DF concentrate were incorporated. Thus, S3 and S6 samples exhibited similar free fatty acid profiles to the control throughout ripening.

Simple modelling of air drying curves of fresh and osmotically pre-dehydrated apple cubes

Abstract Air drying curves simulation of fresh and pre-osmosed apple cubes was carried out through a diffusional mass transfer model solved by the separation of variables method. The influence of an osmotic pre-treatment of apple samples on air drying curves was evaluated. Drying curves of fresh apple cubes showed case-hardening when the air drying temperature was higher than 60 °C, and the drying curves simulation was rendered inaccurate (%var = 92.9%). The effective diffusivity coefficient in the air drying process was considerably affected by the previous application of osmotic drying (70 °Brix sucrose at 50 °C) between 30 and 180 min( D eff decreased 38–64%). However, the duration of this treatment did not show an important influence on this diffusivity. Simulation of the air drying curves of osmotically pre-dried samples was carried out satisfactorily when neglecting sample shrinkage in the proposed model (%var = 98.4%).

Drying of shrinking cylinder-shaped bodies

Abstract A mathematical model has been developed for the prediction of sample temperature, average moisture and moisture distribution in a cylinder-shaped solid during the drying process. The effect of shrinkage was taken into account. The macroscopic heat balance and the microscopic mass balance combined with Ficks law were simultaneously solved using the Runge-Kutta-Merson method and a numerical finite difference method. The effective diffusion coefficient was expressed as a function of sample temperature and local moisture content. Using an experimental drying curve determined at 90 °C, the diffusional equation was identified for broccoli stems, and was used to predict the average and local moisture content variations during the process. Good agreement with experimental results was found (average percentage of explained variance was 99.8%).

Composition assessment of raw meat mixtures using ultrasonics.

The use of ultrasonic velocity measurements to determine the composition of dry fermented sausages was assessed. Mixtures of ground lean and fatty tissues were prepared to cover a wide range of fat (2-90 wt.%), moisture (7-76 wt.%), and protein (2-21 wt.%) contents. The ultrasonic velocity in fat decreased on average 5.6 ms(-1) per °C increase in temperature, due to the negative temperature coefficient for fat and the fat melting, which is observed in (DSC) differential scanning calorimetry analysis. The ultrasonic velocity temperature dependence allowed the determining of the fat, moisture and protein+others content, by measuring the ultrasonic velocity in the mixtures at 4 and 25°C and using a semi-empirical equation. The explained variance was 99.6% for fat, 98.7% for moisture and 85.4% for protein+others. The results obtained show the feasibility of using ultrasonic velocity measurement to assess the composition of meat products such as dry fermented sausages, rapidly and non-destructively.

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.

Effect of power ultrasound application on aqueous extraction of phenolic compounds and antioxidant capacity from grape pomace (Vitis vinifera L.): Experimental kinetics and modeling

The kinetics of both conventional (mechanical stirring, 200rpm) and acoustic (55±5kHz, 435±5W/L) aqueous extraction of total phenolic content and antioxidant capacity from grape pomace by-products (Vitis vinifera L.) have been experimentally evaluated and modeled at different extraction temperatures (20, 35 and 50°C). A gradual and significant increase of total phenolic content and antioxidant capacity of the extracts was observed as the temperature increased, the highest values being obtained in the case of the extraction assisted acoustically. According to the results, the acoustic assistance of the extraction process led to aqueous extracts with phenolic and antioxidant characteristics similar to those obtained with mechanical stirring, working under lower temperature conditions and during less operating time. Specifically, the conventional extraction of total phenolics at 35 and 50°C did not differ significantly from extractions assisted with power ultrasound at 20 and 35°C, respectively; and the acoustic process required approximately 3, 4 and 8 times less time, at 20, 35 and 50°C, than the conventional extraction to obtain extracts with similar characteristics. The extraction curves obtained for total phenolic content and antioxidant capacity, measured by the ABTS and FRAP methods, were properly represented by a modified Weibull model for both conventional and acoustic extractions within the temperature range 20-50°C, presenting an average percentage of explained variance⩾97.9%, and an average mean relative error⩽7.0%. A high correlation (r(2)⩾0.992) was observed between the experimental and simulated values for all the quality attributes in study.