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ABSTRACT: The aim of this work was to evaluate the effect of operating conditions on the quality of dried foods, monitoring shrinkage,
rehydration capacity, and color changes. Carrot samples of different shapes and dimensions were dried in a convective oven
by air whose temperature and velocity were chosen in a range of physical significance. Two values of air velocity, i.e., 2.8
and 2.2m/s, were considered; air temperature was chosen equal to 50°C, 70°C, and 85°C. It was observed that more drastic
drying conditions indeed improved the drying rate, but were also responsible for a decrease of food rehydration capacity.
Food behavior was observed comparing some characteristic parameters as obtained upon fitting the experimental data by simple
modeling equations. In particular, the drying curves were fitted by the Newton’s model, whereas, shrinkage was modeled by
a linear relationship between volume variation and moisture content. Rehydration capacity was estimated by water regain percentage,
which was evaluated after 5h.
KeywordsDrying–Carrots–Shrinkage–Color–Rehydration
Food and Bioprocess Technology 04/2012; 5(1):118-129. · 3.70 Impact Factor
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ABSTRACT: The aim of this work was to estimate shrinkage, apparent density changes, and the effective diffusion coefficient of water, Deff , during eggplant drying. Drying experiments were performed using a halogen moisture analyzer. This technology has several advantages over the traditional methods reported in the literature, as it is quite inexpensive, requires less energy, and, in principle, can be used for many different types of foods. The experimental data were interpreted using a classical mathematical model that describes the transient mono-dimensional transport of water in food to estimate Deff . Under the experimental conditions examined, the Deff, was found to range from 1.13.10−10 to 5.65.10−10 m2/s. Shrinkage modelling revealed a non-linear dependence of food sample volume on the food's moisture content. In addition, while the apparent density of the food did not change appreciably during the first period of drying, a marked decrease was observed during the final drying period.
International Journal of Food Properties 05/2011; 14(3):523-537. · 0.67 Impact Factor
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ABSTRACT: A central composite design (CCD) was performed to evaluate the effects of four factors, i.e. temperature (T), pH, agitation rate (K) and initial lactose concentration (L), on ricotta cheese whey batch fermentation and to optimize the process leading to the formation of bio-ethanol. Anaerobic batch fermentation experiments were carried out by using the yeast Kluyveromyces marxianus. After a preliminary experimental analysis, the values of the chosen factors were 32 and 40 degrees C for T, 4 and 6 for pH, 100 and 300 rpm for K, 40 and 80 g L(-1) for L. Response surface methodology (RSM) was used to optimize the fermentation process and an empirical polynomial model was used to fit the experimental data. The best operating conditions resulted to be T=32.35 degrees C, pH 5.41, K=195.56 rpm and L=40 g L(-1) and the model ensured a good fitting of the observed data.
Bioresource technology 12/2010; 101(23):9156-62. · 4.25 Impact Factor
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ABSTRACT: The present work is an experimental study of the performance of a recently designed immobilized enzyme: inulinase from Aspergillus sp. covalently immobilized on Sepabeads. The aim of the work is to test the new biocatalyst in conditions of industrial interest and to assess the feasibility of the process in a fluidized bed bioreactor (FBBR). The catalyst was first tested in a batch reactor at standard conditions and in various sets of conditions of interest for the process. Once the response of the catalyst to different operating conditions was tested and the operational stability assessed, one of the sets of conditions tested in batch was chosen for tests in FBBR. Prior to reaction tests, preliminary fluidization tests were realized in order to define an operating range of admissible flow rates. As a result, the FBR was run at different feed flow rates in a closed cycle configuration and its performance was compared to that of the batch system. The FBBR proved to be performing and suitable for scale up to large fructose production.
International Journal of Molecular Sciences 01/2010; 11(3):1180-9. · 2.60 Impact Factor
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ABSTRACT: In this paper, the reaction of enzymatic trans-esterification of glycerides with ethanol in a reaction medium containing hexane at a temperature of 37 degrees C has been studied. The enzyme was Lipase from Mucor miehei, immobilized on ionic exchange resin, aimed at achieving high catalytic specific surface and recovering, regenerating and reusing the biocatalyst. A kinetic analysis has been carried out to identify the reaction path; the rate equation and kinetic parameters have been also calculated. The kinetic model has been validated by comparison between predicted and experimental results. Mass transport resistances estimation was undertaken in order to verify that the kinetics found was intrinsic. Model potentialities in terms of reactors design and optimization are also shown.
Bioprocess and Biosystems Engineering 11/2009; 33(6):701-10. · 1.81 Impact Factor
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ABSTRACT: Three-dimensional models of exoinulinase from Bacillus stearothermophilus and endoinulinase from Aspergillus niger were built up by means of homology modeling. The crystal structure of exoinulinase from Aspergillus awamori was used as a template, which is the sole structure of inulinase resolved so far. Docking and molecular dynamics simulations were performed to investigate the differences between the two inulinases in terms of substrate selectivity. The analysis of the structural differences between the two inulinases provided the basis for the explanation of their different regio-selectivity and for the understanding of enzyme-substrate interactions. Surface analysis was performed to point out structural features that can affect the efficiency of enzymes also after immobilization. The computational analysis of the three-dimensional models proved to be an effective tool for acquiring information and allowed to formulate an optimal immobilized biocatalyst even more active that the native one, thus enabling the full exploitation of the catalytic potential of these enzymes.
Biotechnology Progress 11/2009; 26(2):397-405. · 2.34 Impact Factor
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ABSTRACT: In the present work, olive husk oil was continuously transesterified by immobilized lipases in a fluidized bed reactor (FBR). Preliminary fluidization tests were run to find the fluidization flow rate for the system under study. Subsequently, the reactor was operated continuously performing high productivity, as compared to literature data on packed bed reactors (PBR) for biodiesel production and to batch data reported in this work. The system was also run in a recycle configuration aiming at studying the effect of repeated passages of the substrates within the reactor, without changing fluidization conditions (i.e. decreasing the fresh feed flow rate to the system by increasing the recycle flow rate, without changing the flow rate entering the reactor). Tests at different recycle ratios were performed to investigate the effect on the process performance of different dilution degrees within the reactor and fresh flow rates fed to the system and to find optimal operating conditions. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering 03/2009; 4(3):365 - 368. · 0.76 Impact Factor
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ABSTRACT: The aim of the present work is to analyze the complex phenomena involved in the concentrated milk clotting process in order
to define general criteria applicable to the design of a continuous coagulator. A full characterization of the rheological
properties of completely hydrolyzed milk as a function of two different parameters, i.e., the coagulator temperature and the
concentration degree of the milk, is presented. The dynamic evolution of loss, G′′, and storage, G′, moduli has been obtained
at different frequency values and for different concentration degrees during the clotting process. Time cure tests have been
performed on completely hydrolyzed milk samples showing that the rate of curing is very high and that the time for rheological
experiments is much too short for testing Winter's theory of gelation. To overcome this problem, the intersect of loss and
storage moduli was used for estimating the coagulation. Coagulation is faster when higher temperatures are used and the consistency
of the final curd is greater if a more concentrated milk is used. A tentative physical explanation based on the network theories
is presented. If an observation time far enough from the crossover point is chosen it can be seen that the curd strength estimated
at 40 °C is about 50 times higher than that one evaluated at 25 °C. Among the considered temperatures, a good processing value
was evaluated at 40 °C.
Rheologica Acta 02/2001; 40(2):154-161. · 2.03 Impact Factor
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ABSTRACT: A novel approach in the treatment of olive mill wastewater is presented. Aim of the proposed process is both the reduction of pollution caused by the wastes and the selective separation of some useful products that are present (fats, sugars, polyphenols, etc.). The treatment consists in a preliminary centrifugation step, in which the suspended solids are removed, and in an actual selective separation phase, carried out by ultrafiltration (UF), of the centrifuge supernatant. The combination of centrifugation and ultrafiltration allows a COD reduction of about 90%. Moreover a complete separation of fats, completely rejected by the membrane, from salts, sugars and polyphenols, contained in the permeate, is attained. The present experimental study is directed to investigate the fluid-dynamic aspects related to the ultrafiltration of real olive mill wastewaters. It is based on a preliminary rheological characterization of the waste and on the evaluation of permeation efficiency that was analyzed as a function of several parameters such as the importance of pre-treating wastewater, the effects of localized turbulence, promoted by UF module geometry, and of the main operating variables (trans-membrane pressure and feed flow rate). UF experimental results, obtained in a lab-scale flat-sheet membrane module, are interpreted using both the cake-filtration and the resistance-in-series models, thus allowing the evaluation of Rf parameter that represents the effect of fouling on separation efficiency. An estimation of specific cake resistance, α, is, therefore, performed on the basis of the feed concentration of total non-water compounds present in the waste showing that pre-treated wastewaters give a lower α with respect to raw wastewaters by a factor of about 1000. Moreover, it is found that at the same TMP, lower values of α correspond to a greater Re and that higher local turbulence implies lower specific cake resistances. The results obtained in the present paper could give useful indications for a preliminary characterization of pilot and industrial modules utilized for olive mill wastewaters treatment aimed at a significant COD reduction and a selective separation of valuable compounds that are present in the waste.
Journal of Membrane Science.
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ABSTRACT: In this work, the fermentation of “ricotta cheese whey” for the production of ethanol was simulated by means of a multiple hybrid neural model (HNM), obtained by coupling neural network approach to mass balance equations for lactose (substrate), ethanol (product) and biomass. A HNM represents an alternative method that may allow predicting the behaviour of complex systems, such as biotechnological processes, in a more efficient way. Some well-assessed phenomena, in fact, are described by a fundamental theoretical approach; some others, being very difficult to interpret, are analysed by means of rather simple “cause–effect” models, based on artificial neural networks. The experimental data, necessary to develop the model, were collected during batch fermentation runs. For all the proposed networks, the inputs were chosen as the operating variables with the highest influence on reaction rate. Simulation results showed the ability of the developed model to represent the process dynamics. The HNM was capable of an accurate representation of the system behaviour by predicting biomass, lactose and ethanol concentration profiles with an average error percentage lower than 10%. Moreover, the hybrid approach showed the ability to limit error propagation into the models that can be caused by the purely black-box nature, typical of neural networks.
Computers & Chemical Engineering.
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ABSTRACT: The aim of this paper is the presentation of a novel system for continuous monitoring of the operating variables involved in ultrafiltration process. The proposed system is based on the utilization of a data acquisition set, consisting of field point units supplied by National Instruments, connected to a Personal Computer, thus allowing UF module performance monitoring. It is, therefore, possible to continuously measure permeate flux decay and to control membrane fouling by means of a device, controlled by the PC, that is able to generate pulses on both trans-membrane pressure and feed flow rate. This device, already patented by the authors [1], is comprised by a system of electric valves that, during a standard cross-flow operation, prime, without any plant stop or any flux inversion, a “cleansing” procedure for the membrane. The main advantages related to the utilization of this device are: the improvement of both performances and efficiency of membrane cross-flow operations, its simplicity and the economy of its installation, the reduction of the dead times due to plant stops and to traditional cleaning procedures. The application of the proposed system to the BSA ultrafiltration showed a significant increase of permeate fluxes with respect to a traditional cross-flow filtration plant.
Desalination.
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ABSTRACT: In the present work a deactivation model for an inulinase from Aspergillus niger is presented; a first order kinetic is found and the deactivation constant kd is related to temperature through the Arrhenius model. The deactivation model was satisfactorily validated and implemented into a kinetic model for inulin hydrolysis predictions; the result is a complete model that is able to predict reaction performances for substrate concentrations ranging between 10 and 40 g/l and reaction temperature up to 60 °C, even on a long time scale. The model is also shown to be a powerful tool to understand reaction paths and to choose the optimal reaction conditions for long time scale processes. A relevant problem for enzymatic process temperature optimization is formulated and solved by means of the predictive model determined.
Biochemical Engineering Journal.
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ABSTRACT: The present work reviews the main advancements achieved in the last decades in the study of the fructose production process by inulin enzymatic hydrolysis. With the aim of collecting and clarifying the majority of the knowledge in this area, the research on this subject has been divided in three main parts: a) the characteristics of inulin (the process reactant); b) the properties of the enzyme inulinase and its hydrolytic action; c) the advances in the study of the applications of inulinases in bioreactors for fructose production. Many vegetable sources of inulin are reported, including information about their yields in terms of inulin. The properties of inulin that appear relevant for the process are also summarized, with reference to their vegetable origin. The characteristics of the inulinase enzyme that catalyzes inulin hydrolysis, together with the most relevant information for a correct process design and implementation, are described in the paper. An extended collection of data on microorganisms capable of producing inulinase is reported. The following characteristics and properties of inulinase are highlighted: molecular weight, mode of action, activity and stability with respect to changes in temperature and pH, kinetic behavior and effect of inhibitors. The paper describes in detail the main aspects of the enzyme hydrolysis reaction; in particular, how enzyme and reactant properties can affect process performance. The properties of inulinase immobilized on various supports are shown and compared to those of the enzyme in its native state. Finally, a number of applications of free and immobilized inulinases and whole cells in bioreactors are reported, showing the different operating procedures and reactor types adopted for fructose production from inulin on a laboratory scale.
Critical Reviews in Biotechnology 27(3):129-45. · 6.47 Impact Factor
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ABSTRACT: The aim of the present work is the formulation of a theoretical model describing the simultaneous transfer of momentum, heat and mass occurring in a convective drier where hot dry air flows under turbulent conditions around a food sample. The proposed model does not rely on the specification of interfacial heat and mass transfer coefficients and, therefore, represents a general tool capable of describing the behavior of real driers over a wide range of process and fluid-dynamic conditions. The system of non-linear unsteady-state partial differential equations modeling the behavior of a cylindrical-shaped vegetable sample in a drier, has been solved by using finite elements method. It has been observed that air characteristics influence drying performance only when external resistance to mass transfer is the rate controlling step. An experimental study was undertaken which shows very good agreement between model predictions and experimental results.
Journal of Food Engineering. 87(4):541-553.
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ABSTRACT: The behavior of membrane bioreactors operating in recycle configuration is characterized from both a theoretical and an experimental point of view. The theoretical model is based on the unsteady-state balance equations governing momentum and mass transfer within the regions that can be identified in a membrane reactor with immobilized enzyme, coupled to the unsteady-state mass balance on the components in feed tank. The resulting system of non-linear partial differential equations has been numerically solved by Finite Elements Method (FEM), implemented by a commercial package called FEMLAB. The available CFD code allowed determining the time evolution of both velocity and concentration profiles without resorting to considerable simplification hypotheses. As far as the reaction term in the mass balance equations is concerned, reference has been made to lactose hydrolysis catalyzed by immobilized β-galactosidase, also carried out in the experimental part of this work. The chemical reaction is supposed to take place solely in the membrane dense and spongy layers where biocatalyst is actually confined and distributed according to its concentration ratio E3/E2. A set of intrinsic kinetic constants, obtained from the literature, has been used to evaluate the actual reaction rate thus evaluating the effects of immobilization on enzyme activity. The contribution of the most significant transport mechanisms affecting reactor performance has been determined analyzing the dynamic evolution of three representative parameters, i.e. the effectiveness factor, the degree of conversion within the membrane and the bioreactor performance index, as functions of the operating conditions. The proposed transport model is very general as it may describe the behavior of different types of heterogeneous reacting systems by just adapting either the reaction rate expression or the set of intrinsic kinetic constants. An experimental analysis of system behavior has validated the theoretical predictions, showing a good agreement between experimental and theoretical results.
Journal of Membrane Science.
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ABSTRACT: In this paper, a reaction scheme for fructose production by inulin enzymatic hydrolysis is proposed, taking into account the possibility of dealing with a mixture of enzymes acting on a mixture of polymers as substrate. The scheme is subsequently simplified to obtain a stoichiometric relationship between the fructose product and the reacted substrate. The former may be measured by HPLC, while the latter is the subject of kinetic investigations. Our proposed kinetic model is defined within temperature and substrate concentration ranges of industrial interest (40–60 °C and 3–60 g/L, respectively). Some assumptions were made in order to simplify the model, which is based on a minimum number of parameters. These hypotheses were always specified and assumed only on the basis of convenience and rational consideration. Eventually, the kinetic model was successfully validated by comparison with a vast set of experimental results.
Process Biochemistry.
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ABSTRACT: The behavior of a hollow fiber (HF) membrane bioreactor with entrapped biocatalyst is analyzed and characterized from a theoretical point of view. The model is based on the numerical solution of the dimensionless balance equations governing mass transfer within the regions that can be defined for this reacting system, namely the fiber lumen, the membrane dense and spongy layers. The chemical reaction is supposed to take place solely in the last two regions (skin and sponge) where the biocatalyst is confined by entrapment and distributed according to the ratio E3/E2. The evaluation of the significant transport mechanisms of the substrate consumption rates, and more generally of the reactor performance have been carried out by analyzing two representative parameters, i.e. the effectiveness factor and the performance index, as functions of the operating conditions, expressed in terms of a set of characteristic dimensionless groups. The enzyme distribution ratio, E3/E2, its overall loading, the applied trans-membrane pressure (TMP) difference, the substrate feed concentration were investigated as the system key parameters. The reaction kinetics have been modeled with reference to Michaelis–Menten rate equation, modified to account for possible substrate and product inhibition. The results of the theoretical analysis enable to predict an optimal value of TMP and, therefore, of the permeate flux, as a trade-off between the necessity of reducing the transfer resistances in the substrate access to enzyme and that of allowing suitable residence time. The bioreactor performances are no longer affected by the distribution ratio E3/E2, once that this parameter has reached almost unity value : this means that the enzyme can be effectively immobilized just in the membrane spongy region, with the advantage of a significant system simplification from both a technological and an economic standpoint. The model, however, is quite general and can be applied also to different reacting systems, in order to evaluate how the catalyst position within a specific support can affect their performances. A comparison between the theoretical model predictions and some literature experimental data has been also attempted, showing a good agreement for some typical operating conditions.
Journal of Membrane Science.
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ABSTRACT: In this work, the fermentation of "Ricotta cheese whey" for the production of ethanol was simulated by means of a Hybrid Neural Model (HNM), obtained by coupling neural network approach to mass balance equations describing the time evolution of lactose (substrate), ethanol (product) and biomass concentrations. The realized HNM was compared with a pure neural network model (NM) and the advantages gained from the hybrid approach were emphasized. The experimental data, necessary to develop the model, were collected during batch fermentation runs. For all the proposed networks, the inputs were chosen as the operating variables exhibiting the highest influence on the reaction rate. The simulation results showed that the HNM was capable of an accurate representation of system behavior by predicting biomass, lactose and ethanol concentration profiles with an average error percentage lower than 10%. Moreover, especially if compared with the NM, the HNM showed good forecasting capability even with fermentation run never seen during the training phase.
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ABSTRACT: The aim of this paper is to present an innovative methodology for the control of permeate flux decay in membrane separation processes. An artificial neural network (ANN) has been built on the basis of the experimental results collected during ultrafiltration of BSA solutions under pulsating conditions. ANN can predict very accurately real system behavior with relative errors at most reaching 5% in post-simulation analysis. The observed reliability of neural network prediction, suggested an optimal control application of ANN aimed at searching a pulsation frequency profile that could maximize the permeate flux. The control system has been developed by the integration of two different computational environments, that allow actuating a specific control action so that UF experiments are performed in the exact conditions suggested by neural network. This control action is accomplished by a procedure that is invoked whenever the “best” operating time value, function of the current value of feed flow rate, is to be calculated. The generation of suitable pulses obtained on the basis of neural network prediction is, therefore, attained. Several experimental tests aimed at the validation of the present methodology have been performed on a lab-scale UF module. It was found that the utilization of an operating time profile allows obtaining a significant improvement of UF performance as compared to the cases in which either no pulse or constant pulse frequency were used.
Journal of Membrane Science.
