Neural and hybrid modeling: an alternative route to efficiently predict the behavior of biotechnological processes aimed at biofuels obtainment.

The present paper was aimed at showing that advanced modeling techniques, based either on artificial neural networks or on hybrid systems, might efficiently predict the behavior of two biotechnological processes designed for the obtainment of second-generation biofuels from waste biomasses. In particular, the enzymatic transesterification of waste-oil glycerides, the key step for the obtainment of biodiesel, and the anaerobic digestion of agroindustry wastes to produce biogas were modeled. It was proved that the proposed modeling approaches provided very accurate predictions of systems behavior. Both neural network and hybrid modeling definitely represented a valid alternative to traditional theoretical models, especially when comprehensive knowledge of the metabolic pathways, of the true kinetic mechanisms, and of the transport phenomena involved in biotechnological processes was difficult to be achieved.

Optimization of ricotta cheese whey (RCW) fermentation by response surface methodology.

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.

Fructose production by inulinase covalently immobilized on sepabeads in batch and fluidized bed bioreactor.

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.

Kinetics of enzymatic trans-esterification of glycerides for biodiesel production.

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.

The state of the art in the production of fructose from inulin enzymatic hydrolysis.

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.