Revisiting the maximum conversion of substrate in an enzymatic cstr with micromixing considerations

The balance equations pertaining to an enzyme undergoing first order thermal deactivation and a substrate undergoing enzyme-catalyzed transformation following Michaelis-Menten kinetics in a CSTR are solved for the two limits of micromixing. The maximum conversions of substrate are obtained under the assumption that the space time of the reactor is infinite. The range of the maximum conversion of substrate is wider at intermediate values for the dimensionless Michaelis-Menten constant and becomes narrower as the ratio of the time scales of the enzyme-catalyzed reaction and the enzyme deactivation increases. On a résolu pour les deux limites du micromélange les équations d'équilibre d'une enzyme subissant une désactivation thermique de premier ordre et d'un substrat subissant une transformation catalysée par l'enzyme suivant la cinétique de Michaelis-Menten dans un réacteur agité continu (CSTR). Les conditions maximales de conversion du substrat sont obtenues en partant de l'hypothèse que l'espace-temps du réacteur est infini. La gamme de conversion maximale du substrat est plus large aux valeurs intermédiaires pour la constante adimensionnelle de Michaelis-Menten et se rétrécit lorsque les échelles de temps de la réaction catalysée par l'enzyme et la déactivation de l'enzyme augmentent

On the optimum distribution of enzyme feed in a cascade of CSTR's performing an enzyme-catalyzed reaction with deactivation

A search for the optimum fractional distribution of an enzyme-rich stream to the various reactors of a cascade of CSTR's was implemented. A theoretical analysis, laid out in dimensionless form and based on the assumptions that the system is operated under steady state conditions, the enzyme undergoes first order deactivation, and the reaction catalyzed by the enzyme follows Michaelis-Menten kinetics, is reported. The objective function utilised is the minimisation of the overall volume of the cascade, and analytical expressions are obtained for the concentration of active enzyme and substrate in the outlet stream from each reactor. It is found that the best option is to add the whole enzyme-rich stream to the first reactor in the cascade irrespective of the operating and kinetic parameters of the system

How performance of integrated systems of reaction and separation relates to that of parallel and sequential configurations

Given the thermodynamic and kinetic limitations which often constrain the extent of chemical reactions and post-reactional separation processes, and therefore constrain the yield and the degree of purity of the resulting products, integration of reaction and separation in a single unit has been under the scope of several bioengineering researchers in recent years. It is the aim of this work to compare the performance of a cascade of N reactor/separator sets, either in series or in parallel, with that of an integrated reaction/separation unit. In order to do so, a Michaelis-Menten reaction in dilute substrate solutions (i.e. a pseudo ®rst order reaction) was considered to take place in either con®guration and, under the same reaction and separation conditions, comparison of the performance and ef®ciency of these con®gurations was made in terms of fractional recovery of pure product, total time required to achieve such recovery and rate of recovery. It was concluded that: (i) the series combination of reactor/separator sets yields better results, both in terms of fractional amount of product recovered and time required to do so, than the parallel combination; and (ii) the integrated approach is much more time- and cost-effective than plain cascading, thus making it very attractive from an economic point of view

Partial identification of water-soluble peptides released at early stages of proteolysis in sterilized ovine cheese-like systems: Influence of type of coagulant and starter

Cheese-like systems were manufactured from sterilized ovine milk, using crude aqueous extracts of Cynara cardunculus or cardosin A isolated therefrom as clotting agent. The effect of adding a commercial starter culture was also assessed. The impact of the type of coagulant used during the initial 24 h of proteolysis was evaluated via separation of peptides in the watersoluble extracts by reverse-phase HPLC, followed by partial sequencing via Edman degradation. Cardosin A accounted for most events of primary proteolysis. The major cleavage sites were Phe105-Met106 in κ-casein, and Leu127-Thr128, Ser142-Trp143, Leu165-Ser166, and Leu190-Tyr191 in β-casein. The starter culture did not play an active role during the initial stages of ripening

Optimal temperature and concentration profiles in a cascade of CSTR's performing Michaelis-Menten reactions with first order enzyme deactivation

A necessary condition is found for the intermediate temperatures and substrate concentrations in a series of CSTR's performing an enzyme-catalyzed reaction which leads to the minimum overall volume of the cascade for given initial and final temperatures and substrate concentrations. The reaction is assumed to occur in a single phase under steady state conditions. The common case of Michaelis-Menten kinetics coupled with first order deactivation of the enzyme is considered. This analysis shows that intermediate stream temperatures play as important a'role as intermediate substrate concentrations when optimizing in the presence of nonisothermal conditions. The general procedure is applied to a practical example involving a series of two reactors with reasonable values for the relevant five operating parameters. These parameters are defined as dimensionless ratios involving activation energies (or enthalpy changes of reaction), preexponential factors, and initial temperature and substrate concentration. For negligible rate of deactivation, the Qptimality condition corresponds to having the ratio of any two consecutive concentrations as a single-parameter increasing function of the previous ratio of consecutive concentrations

Secondary proteolysis in Serra cheese during ripening and throughout the cheese-making season

Experimental Serra cheeses were manufactured from raw ewe’s milk and thistle flowers following a two-way factorial design. The content of nitrogen soluble in water (WSN), in 2% trichloroacetic acid (2% TCA-N), in 12% TCA (TCA-N) and in 5% phosphotungstic acid (5% PTA-N), and the pH and salt-in-moisture concentration were measured throughout the ripening period (sampling at 0, 7, 21 and 35 days) and the cheese-making season (sampling in November, February and May). Proteolysis in 35-day-old Serra cheese was quantitatively high [average values of 34.6% and 11.9% for WSN/TN (total nitrogen) and 2% TCA-N/TN, respectively], but qualitatively low (average values of 5.8% and 1.2% for 12% TCA-N/TN and 5% PTA-N/TN, respectively). The ratios WSN/TN and 2% TCA-N/TN were lowest for cheeses ripened in February, whereas the ratio 12% TCA-N/TN was highest for cheeses ripened in November. By 35 days of ripening, the average pH and salt-in-moisture concentration values were 5.2 and 4.8%, respectively. No correlation was found to occur between the measured pH or salt-in-moisture concentration and the values of soluble nitrogen fractions throughout the cheese-making season

Comparative biochemical evolution during ripening of bovine, ovine and caprine cheeses manufactured with extracts of flowers of Cynara cardunculus

Changes in the main physicochemical and biochemical characteristics of bovine, ovine and caprine milk cheeses manufactured with aqueous extracts of flowers of Cynara cardunculus were studied throughout ripening (0 – 68 days). At the end of ripening the pH in the centre was (mean ± ISD) 5.05±0.07, 5.15±0.21 and 4.91±0.07 for bovine, ovine and caprine milk cheeses, respectively; whereas the pH at the top of the cheese was 5.21±0.09, 5.44±0.12 and 5.12±0.07, respectively; the moisture content values of bovine, ovine and caprine milk cheeses were 37.68±2.32, 40.23±4.34 and 45.73±1.44%, respectively; the NaCl content values were 4.00±0.43, 4.00±0.56 and 4.08±0.58 (%TS); the fat content values were 41.01±5.32, 63.60±7.80 and 45.14±9.14 (%TS); the protein content values were 28.96±1.84, 22.89±2.37 and 30.02±1.22 (%TS); the water-soluble nitrogen values were 32.91±1.76, 46.44±1.86 and 48.72±1.08 (%TN); the values of nitrogen soluble in trichloroacetic acid were 10.25±1.93, 10.41±2.91 and 7.25±0.84 (%TN); the values of nitrogen soluble in phosphotungstic acid were 1.50±0.18, 1.87±0.65 and 1.38±0.32 (%TN); finally, the free amino acid content values were 21.33±5.34, 17.51±5.08 and 23.93±4.80 μM equivalents of leucine. Urea-polyacrylamide gel electrophoresis of water-insoluble fractions from cheeses indicated high degrees of proteolysis of αs1-casein in bovine cheeses and more extensive proteolysis of the αs-casein region in caprine than in ovine cheeses, but a moderate degree of proteolysis of β-casein in all types of cheese; electrophoregrams of the water-soluble fraction displayed increasing numbers of bands throughout ripening, an observation that is consistent with the increase in the ratio of water-soluble nitrogen to total nitrogen

Interesterification and acidolysis of butterfat with oleic acid by Mucor javanicus lipase: changes in the pool of fatty acid residues

Lipases have become powerful tools in the manufacture of structured fats either via randomization of their glyceride composition or incorporation of externally supplied fatty acid residues in such glycerides. The present communication reports on changes that occurred in the fatty acid pool of anhydrous butterfat subject to interesterification and to acidolysis with oleic acid catalyzed by a commercial lipase immobilized by plain physical adsorption onto hydrophobic hollow fibers at 40°C under controlled water activity. The main goal of this research effort was to engineer butterfat so as to increase its level of unsaturated fatty acid residues and concomitantly decrease its level of medium- and long-chain saturated fatty acid residues (viz. lauric and myristic acids). Although a certain degree of net hydrolysis of butterfat was observed, the triacylglycerols of butterfat subject to acidolysis were found to possess more (approximately 30% w/w) oleic acid and significantly less (8% w/w) lauric acid and less (2% w/w) myristic acid than those of the original butterfat