A. Femenia

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.

Ultrasound-assisted extraction of pectins from grape pomace using citric acid: A response surface methodology approach

An ultrasound-assisted procedure for the extraction of pectins from grape pomace with citric acid as the extracting agent was established. A Box-Behnken design (BBD) was employed to optimize the extraction temperature (X1: 35-75°C), extraction time (X2: 20-60 min) and pH (X3: 1.0-2.0) to obtain a high yield of pectins with high average molecular weight (MW) and degree of esterification (DE) from grape pomace. Analysis of variance showed that the contribution of a quadratic model was significant for the pectin extraction yield and for pectin MW whereas the DE of pectins was more influenced by a linear model. An optimization study using response surface methodology was performed and 3D response surfaces were plotted from the mathematical model. According to the RSM model, the highest pectin yield (∼32.3%) can be achieved when the UAE process is carried out at 75°C for 60 min using a citric acid solution of pH 2.0. These pectic polysaccharides, composed mainly by galacturonic acid units (<97% of total sugars), have an average MW of 163.9 kDa and a DE of 55.2%. Close agreement between experimental and predicted values was found. These results suggest that ultrasound-assisted extraction could be a good option for the extraction of functional pectins with citric acid from grape pomace at industrial level.

Ultrasonic determination of the composition of a meat-based product

Abstract The use of ultrasonics as an analytical technique to estimate the composition of a fermented meat-based product (sobrassada) was assessed. Moisture, fat and protein contents and ultrasonic velocity at 4, 8, 12 and 25 °C were measured in samples using different formulae. In this study, it was considered that a meat-based product is formed of three different constituents: fat, water and protein+others. Ultrasonic velocity was related, by a semiempirical equation, to the composition and the ultrasonic velocity of the above three components. The ultrasonic velocity temperature dependence allowed the determination of fat, moisture and protein+others contents. The explained variance was 98.0% for protein+others, 97.6% for fat and 95.6% for moisture. The results obtained show the feasibility of using ultrasonic velocity measurement to assess, in a rapid and non-destructively way, the composition of a meat-based product.

A Diffusional Model with a Moisture-Dependent Diffusion Coefficient

Many investigators point out that a more realistic diffusion model is obtained when the effective diffusivity is considered with both temperature and moisture content dependent. Two mathematical models to predict the drying curves of pineapple at different temperatures have been compared. The simulation provided by model I, where the effective diffusion coefficient was considered as a function of the temperature, was unsatisfactory as indicated by the mean relative error (%E) of 19.8 ± 2.4%. The diffusion equation was modified by including both the effect of the temperature and the local moisture content on the effective diffusion coefficient in model II, being the %E of the simulation of 4.5 ± 2.0%.

Ultrasound-assisted extraction of hemicelluloses from grape pomace using response surface methodology

An ultrasound-assisted procedure was applied to the extraction of hemicelluloses from grape pomace at a mild temperature (20°C). A Central composite design (CCD) was employed to optimize the ultrasound-assisted extraction (UAE) of hemicelluloses from grape pomace with the aim to maximize their extraction yield, and, also, the obtention of the main polymers forming this fraction: Xyloglucans (XLG), Mannans (MAN) and Xylans (XN). Extraction time (X1), solid:liquid ratio (X2) and KOH concentration (X3) were the variables used to optimize the process. The conditions that maximize (1) the extraction yield of hemicelluloses and the contents of (2) XLG, (3) MAN and (4) XN, were: (1) X1=2.6h; X2=1:48 (w/v); X3=0.4M, (2) X1=2.9h; X2=1:57 (w/v); X3=2.25M, (3) X1=2.7h; X2=1:58(w/v);X3=2.2M, and (4) X1=3h; X2=1:60 (w/v); X3=2.3M, respectively. Under these conditions, the maximum extraction yield of hemicelluloses, XLG, MAN and XN contents were: ∼7.9±0.2%, ∼3.6±0.02%, ∼1.1±0.04% and ∼1.2±0.02%, respectively. Close agreement between experimental and predicted values was found. The results suggest that the ultrasound-assisted extraction could be a good option for the extraction of hemicellulosic polysaccharides from grape pomace at industrial level.

Optimization of the Drying Process of Carrot (Daucus carota v. Nantes) on the Basis of Quality Criteria

The drying curves and the degradation kinetics of three different quality attributes (total carotenoids (TC) and total polyphenols (TP) contents and antioxidant activity (AA)) of carrots during drying at different temperatures (from 40 to 90°C) have been experimentally evaluated and modeled. A diffusional model taking into account the solid shrinkage and both the external and internal water transfer resistances was used to accurately represent the water transfer in carrot during drying (average mean relative error (MRE) of 3.3 ± 0.6%). The effective moisture diffusivity was found to follow the Arrhenius relationship (Ea = 76.0 kJ/mol) and the mass transfer coefficient a linear dependence with air temperature. The Weibull model was used to satisfactorily simulate the degradation kinetics of the three quality attributes considered (average MRE of 2.8 ± 1.2% for TC content, 5.7 ± 1.0% for TP content, and 3.6 ± 1.8% for AA); these were the Ea of 52.7 kJ/mol for TC; 22.1 kJ/mol for TP; and 27.5 kJ/mol for AA kinetics. By using the proposed models, the estimated optimum drying temperature to best retain the total carotenoids content ranged between ca. 42–46°C; meanwhile, in order to maintain the TP content and the antioxidant activity at the highest levels, the drying needed to be carried out at temperatures of ca. 60–75°C. These results indicate that the TC retention is more influenced by the drying temperature, while the TP and AA retentions are more sensitive to drying time exposure. However, it was possible to establish a global optimum air temperature which ranged between 52.6 and 57.7°C, decreasing the TC, TP, and AA retentions by less than 2.2% from their respective optimal values.

Mathematical Modeling of Moisture Distribution and Kinetics in Cheese Drying

In the cheese industry, the longest phase in the manufacture of cheese is ripening, during which a considerable loss of water occurs. An understanding of the mass transfer mechanisms of drying would thus contribute to improving engineering design and the quality of the final product. In this work, a mathematical model for a cubic shape was proposed to predict the drying kinetics and moisture distribution during cheese drying. The model was developed taking into consideration both the external and internal resistances to mass transfer and an effective diffusion dependent on local moisture and temperature. Furthermore, a specific model for sorption isotherms was established from experimental results and used to complete the overall model formulation. The drying experiments were carried out at 6.3, 12.2, and 18.2°C and 1.0 m s−1 until a moisture content of approximately 0.30 kg kg−1 (db) was reached. Moisture distribution was experimentally measured from the center of the cheese cube to the center of the surfaces and to the vertexes using a time-domain nuclear magnetic resonance (TD-NMR) method. The proposed model was solved using a finite element method and validated by comparing the experimental moisture profiles with those simulated by the model. A satisfactory simulation was obtained for both the drying curves and the moisture profiles. For both groups of data, a mean relative error lower than 6% and a percentage of explained variation higher than 97% was achieved.

Effect of different drying procedures on the bioactive polysaccharide acemannan from Aloe vera ( Aloe barbadensis Miller)

The main effects of different drying procedures: spray-, industrial freeze-, refractance window- and radiant zone-drying, on acemannan, the main bioactive polysaccharide from Aloe vera gel, were investigated. All the drying procedures caused a considerable decrease in the acemannan yield (∼40%). Degradation affected not only the backbone, as indicated by the important losses of (1→4)-linked mannose units, but also the side-chains formed by galactose. In addition, methylation analysis suggested the deacetylation of mannose units (>60%), which was confirmed by 1H NMR analysis. Interestingly, all these changes were reflected in the functional properties which were severely affected. Thus, water retention capacity values from processed samples decreased ∼50%, and a reduction greater than 80% was determined in swelling and fat adsorption capacity values. Therefore, these important modifications should be taken into consideration, since not only the functionality but also the physiological effects attributed to many Aloe vera-based products could also be affected.

Optimisation of the addition of carrot dietary fibre to a dry fermented sausage (sobrassada) using artificial neural networks

An optimisation problem was formulated to maximise the amount of carrot dietary fibre (CDF) in a dry fermented sausage, while maintaining product quality, by using 0-12% CDF as the decision variable, and limiting values of several physico-chemical and textural parameters (moisture content, water activity, pH, colour, non-protein nitrogen, free fatty acid, compression work and hardness) as constraints. The evolution of each quality parameter during the ripening process was estimated by developing a multi-layer feed forward artificial neural network (ANN), taking into consideration the CDF concentration and the ripening time as independent variables. Results indicate an optimum CDF concentration of 4.9% with a good correlation between experimental and estimated values (mean relative error≤3.35%).