Ruy Sousa

Kinetic model for whey protein hydrolysis by alcalase multipoint-immobilized on agarose gel particles

Partial hydrolysis of whey proteins by enzymes immobilized on an inert support can either change or evidence functional properties of the produced peptides, thereby increasing their applications. The hydrolysis of sweet cheese whey proteins by alcalase, which is multipoint-immobilized on agarose gel, is studied here. A Michaelis-Menten model that takes into account competitive inhibition by the product was fitted to experimental data. The influence of pH on the kinetic parameters in the range 6.0 to 11.0 was assessed, at 50oC. Initial reaction-rate assays in a pHstat at different concentrations of substrate were used to estimate kinetic and Michaelis-Menten parameters, k and KM. Experimental data from long-term batch assays were used to quantify the inhibition parameter, KI. The fitting of the model to the experimental data was accurate in the entire pH range.

Recent trends in the modeling of cellulose hydrolysis

This work reviews recent trends in the modeling of cellulose hydrolysis, within the perspective of application of kinetic models in a bioreactor engineering framework, including scale-up, design and process optimization. From this point of view, despite the phenomenological insight that mechanistic models can provide, the expectation that more detailed approaches could be a basis for extrapolations to different substrates and/or enzymatic pools is still not fulfilled. The complexity of the lignocellulosic matrix, the different mechanisms of catalytic action, the role of mass transfer limitations and the deviations from ideal mixing are important difficulties for the modeler, which will continue to impose more conservative approaches for scale-up. Nevertheless, the search for more robust models is a very important task, provided that the engineer is aware of their limitations. Data-driven, non-mechanistic models such as artificial neural networks, perhaps in combination with other approaches in the so-called hybrid models, is also a promising alternative.

Kinetic study of the enzymatic hydrolysis of sugarcane bagasse

This work presents a kinetic study of the enzymatic hydrolysis of three cellulosic substrates: filter paper (FP), used as a low recalcitrance substrate model; steam exploded sugarcane bagasse (SB); and weak acid pretreated SB (1:20 dry bagasse:H2SO4 solution 1% w/w), the last two delignified with 4% NaOH (w/w). The influence of substrate concentration was assessed in hydrolysis experiments in a shaker, using Accellerase® 1500, at pH 4.8, in 50 mM sodium citrate buffer. Cellulose loads (weightsubstrate/weighttotal) were changed between 0.5%-13% (for FP) and 0.99%-9.09% (for SB). For FP and low loads of steam exploded SB, it was possible to fit pseudo-homogeneous Michaelis-Menten models (with inhibition). For FP and higher loads of steam exploded SB, modified Michaelis-Menten models were fitted. Besides, it was observed that, after retuning of the model parameters, it is possible to apply a model fitted for one situation to a different case. Chrastil models were also fitted and they were the only feasible approach for the highly recalcitrant acid-treated SB.

Design of a fuzzy system for the control of a biochemical reactor in fed-batch culture

Abstract The present work seeks a set of reasoning rules that permit the automatic selection of the start point for inverted sucrose feeding in the Cephalosporin C batch production process, using fuzzy methodology. By monitoring the percentage of CO 2 in the outflow gases, it is possible to observe a point of maximum evolution when the microorganism growth phase finishes. Therefore, the moment when the feeding should begin is characterized by a transition from increasing (positive variations) to decreasing (negative variations) CO 2 evolution rates. A fuzzy controller was then conceptualized to operate on three reasoning levels: attention, action and a protection level to prevent errors produced by the exchange of the drying column used before the analyzer for CO 2 measurement. The algorithm was implemented in C. Two experiments were accomplished to establish, adjust and validate the fuzzy system. The results obtained indicated that the algorithm is robust for the tested conditions, allowing a safe automatic operation.

GMC-fuzzy control of pH during enzymatic hydrolysis of cheese whey proteins

Abstract The pH control of the enzymatic hydrolysis of cheese whey in a continuous-flow, perfectly mixed tank reactor, carried out by alcalase immobilized on agarose gel, was studied here. The partial, tailor-made hydrolysis of whey proteins is a good alternative for adding commercial value to this effluent of the dairy industry. Whey hydrolysis may either change or evidence functional properties of the resulting peptides, increasing their applications. A relevant point in this process is the pH control of the enzymatic reactor. Proteolytic reactions change the pH of the medium, affecting the activity of the enzyme(s). An attractive alternative to the conventional automatic control methods, usually PI or on-off schemes, is the Generic Model Control (GMC) algorithm. However, the control performance of model-based algorithms is known to be vulnerable to biases, inconsistencies, or lack of fitness of the model. This feature is especially evident in systems with non-linear dynamics like pH titration. To circumvent this problem, a hybrid GMC-fuzzy algorithm is proposed. Tuning of the GMC parameters was accomplished successfully according to Ziegler and Nichols’ method. A fuzzy algorithm was coupled to the GMC architecture, taking into account process/model mismatches. Simulations and experimental assays showed that the hybrid system presented a good performance in both regulatory and servo problems.

A kinetic model for hydrothermal pretreatment of sugarcane straw

This work presents kinetic models of cellulose and hemicellulose extraction during hydrothermal pretreatment of sugarcane straw. Biomass was treated under conditions of 180, 195, and 210°C, using a solid/liquid ratio of 1:10 (w/v). In this study, cellobiose, glucose, formic acid and hydroxymethylfurfural (from cellulosic fraction) and xylose, arabinose, acetic acid, glucuronic acid and furfural (from hemicellulosic fraction) were taken into account in the kinetic parameters determination. The global search algorithm Simulated Annealing was used to fit the models. At 195°C/15min, 85% of hemicellulose and 21% of cellulose removal was reached. For the confidence regions, it was observed that it can be broad, which is coherent with the fact that the parameters are highly correlated. Kinetic models proposed for both cellulosic and hemicellulosic fractions degradation fitted well to the experimental data.

ESTIMATION OF MASS TRANSFER PARAMETERS IN A TAYLOR-COUETTE- POISEUILLE HETEROGENEOUS REACTOR

A bench-scale, continuous vortex flow reactor (VFR), with a radius ratio, h, equal to 0.48 and an aspect ratio, G, equal to 11.19 was studied. This reactor may be used in the enzymatic hydrolysis of polypeptides obtained from sweet cheese whey with enzymes immobilized on agarose gel. Operational conditions were 2410 < Req < 11793 and 30-min residence time for glycerol-water, 14% w/w, 27oC (Reax = 1.1) and for water, 38oC (Reax = 1.5). Residence time distributions (RTDs) were obtained after pulse injections of different tracers (including dyed solid particles). Mass transfer coefficients of a lumped-parameter model of the reactor were estimated from these data. Model fitting to experimental data was accurate. Working conditions were selected so that transport properties of the fluids would be similar to the ones in the actual process at the final stages of whey hydrolysis.

Hybrid Model for an Enzymatic Reactor Hydrolysis of Cheese Whey Proteins by Alcalase Immobilized in Agarose Gel Particles

Cheese whey proteolysis, carried out by immobilized enzymes, can either change or evidence functional properties of the produced peptides, increasing the potential applications of this byproduct of the dairy industry. Optimization and scale-up of the enzymatic reactor relies on its mathematical model—a set of mass balance equations, with reaction rates usually given by Michaelis-Menten-like kinetics; no information about the distribution of peptides’ molecular sizes is supplied. In this article, a hybrid model of a batch enzymatic reactor is presented, consisting of differential mass balances coupled to a “neural-kinetic model,” which provides the molecular weight distributions of the resulting peptides.

Modeling the Kinetics of Complex Systems: Enzymatic Hydrolysis of Lignocellulosic Substrates

Lignocellulosic biomass is mainly composed of cellulose, hemicellulose, and lignin. Fuzzy logic, in turn, is a branch of many-valued logic based on the paradigm of inference under vagueness. This paper presents a methodology, based on computational intelligence, for modeling the kinetics of a complex reactional system. The design of a fuzzy interpolator to model cellulose hydrolysis is reported, within the perspective of applying kinetic models in bioreactor engineering. Experimental data for various types of lignocellulosic materials were used to develop the interpolator. New experimental data from the enzymatic hydrolysis of a synthetic substrate, on the other hand, were used to validate the methodology. The accuracy of the results indicates that this is a promising approach to extend the application of models fitted for specific situations to different cases, thus enhancing their generality.

Optimization of chemical engineering problems with EMSO software

EMSO software, a free tool for teaching and academic research, presents a favorable environment for simulation and optimization of chemical engineering problems. Although its use in research activities have been demonstrated in the literature, its application as a supporting tool for educational purposes in process systems engineering courses has not been evaluated. The objective of this paper is to demonstrate that this software is suitable as a tool for educational purposes in process systems engineering courses at undergraduate (complementary elective subject) and graduate levels. To accomplish this task, different cases studies, encompassing different sort of programming formulations, are proposed and solved with different solvers in EMSO.