Sviluppo di un biosensore enzimatico ad enzimi immobilizzati per la misura di acido l-Lattico in sistemi FIA (Flow Injection Analysis).

La misura in tempo reale della concentrazione di acido L-Lattico pu\uf2 essere di rilevante importanza nell\u2019industria alimentare e nella medicina. L\u2019impiego di biosensori enzimatici combinato con i vantaggi dei sistemi per analisi di tipo Flow Injection (FIA) pu\uf2 soddisfare il bisogno di analisi rapide ed accurate. La stabilit\ue0 dei biosensori aumenta significativamente se gli enzimi sono immobilizzati su supporti inerti. In questo studio \ue8 stato quindi sviluppato un biosensore enzimatico per la misura di acido L-Lattico immobilizzando su vetro a porosit\ue0 controllata gli enzimi lattato ossidasi e horseradish perossidasi, che a partire da acido lattico ed in presenza di un determinato sistema reagente catalizzano due reazioni consecutive che portano alla formazione di un prodotto colorato rilevabile in spettrofotometria. Il biosensore sviluppato ha permesso analisi in FIA estremamente riproducibili ma si \ue8 dimostrato instabile per lunghi periodi di esercizio

Continuous production and in situ extraction of isovaleraldehyde in a membrane bioreactor

Bioconversions are generally low productivity processes when compared to chemical synthetic reactions. The productivity of a bioconversion can be maximized if it is carried out in the presence of substrate/product concentrations at which the biocatalyst shows optimal activity and stability. One way to achieve this is to develop a process with continuous addition of the substrate and selective removal of the product. The microbial oxidation of isoamyl alcohol to isovaleraldehyde by a newly isolated Gluconobacter oxydans strain has been reported recently. High conversion yields (>90%) and good rates (maximum yield after 90 min) were obtained in a batch mode. With this strain, although aldehyde dehydrogenase(s) leading to acid formation are present, further oxidation of the aldehyde to acid is significantly slower so that transient accumulation of the aldehyde is possible. The productivity of this bioconversion can be improved by setting up a continuous process with addition of substrate at an adequate flow rate. In situ removal of the aldehyde is imperative to avoid acid production and to reduce evaporation of the product. This chapter describes a membrane-based extractive procedure to achieve an in situ, nondispersive recovery of the aldehyde

Continuous production of isovaleraldehyde through extractive bioconversion in a hollow-fiber membrane bioreactor

A membrane bioreactor was developed to perform an extractive bioconversion aimed at the production of isovaleraldehyde by isoamyl alcohol oxidation with whole cells of Gluconobacter oxydans. A liquid/liquid extractive system using isooctane as extractant and assisted by a hollow-fiber hydrophobic membrane was chosen to recover the product. The aqueous bioconversion phase and the organic phase were maintained apart with the aid of the membrane. The extraction of alcohol and aldehyde was evaluated by performing equilibrium and mass transfer kinetic studies. The bioprocess was then performed in a continuous mode with addition of the substrate to the aqueous phase. Fresh solvent was added to the organic phase and exhausted solvent was removed at the same flow rate. The extractive system enabled a fast and selective in situ removal of the aldehyde from the water to the organic phase. High conversions (72\u201390%) and overall productivity (2.0\u20133.0 g l 121 h 121) were obtained in continuous experiments performed with different rates of alcohol addition (1.5\u20133.5 g l 121 h 121). Cell deactivation was observed after 10\u201312 h of operation

A Multiphasic Hollow Fiber Reactor for the Whole-Cell Bioconversion of 2-Methyl-1,3-propanediol to (R)-\u3b2-Hydroxyisobutyric Acid

This paper describes the bioconversion of 2-methyl-1,3-propanediol to (R)-\u3b2-hydoxyisobutyric acid (HIBA) by Acetobacter ALEI in a hollow fiber membrane bioreaction system arrangement that allows the integration of three liquid phases: the aqueous bioconversion phase, the organic phase consisting of a solution of trioctyl phosphine oxide (TOPO) in isooctane, and the third phase consisting of a basic stripping solution that allows reextraction of HIBA from the organic phase. A comparison of HIBA mass transfer experiments was carried out in the membrane reactor with two and three phases for different pH and TOPO concentrations. The use of the three-phase arrangement allows the extraction of high quantities of HIBA from the aqueous medium (higher than 85%) independently of the pH, whereas in the two-phase system the percentage of HIBA extracted from the aqueous medium was lower, 42% in the best case, and strongly influenced by the pH. The percentage of the extractive agent TOPO in the organic phase influenced on the mass transfer rate in both bi- and triphasic arrangements. By simply integrating the re-extraction phase in the system it was possible to increase the extraction yield by 2-fold, reduce the amount of TOPO by 4-fold, and operate at the more favorable pH 4. A bioconversion experiment was done in these conditions (pH = 4, TOPO = 5%) to confirm the advantages of including the third stripping solution. Fed-batch operation of the triphasic membrane reactor was maintained for more than 20 h, reaching an HIBA concentration in the stripping solution of 29 g L 121