Gaetano Lanzarini

Kinetic and immobilization studies on fungal glycosidases for aroma enhancement in wine

Abstract The biochemical properties of a commercial glycosidase from Aspergillus niger (Cytolase PCL5, Genencor) were investigated. The product contains β-glucosidase, α-arabinosidase, and α-rhamnosidase activities in a ratio considered suitable for aroma enhancement in wine-making. A kinetic study of these three activities was carried out, which included determination of kinetic constants; dependence of enzyme activity and stability on pH and temperature; and enzyme inhibition by glucose, fructose, glycerol, and sulfurous anhydride. These glycosidase activities were immobilized to a solid carrier with the aim of developing a continuous process for wine aroma enhancement. Immobilization was best achieved with silanized bentonite as the solid, activated carrier, with bound glutaraldehyde as the reactive arm at a protein:carrier ratio of 0.11. Immobilization reaction was carried out for 48 h at pH 4 and 30°C. Under these conditions, 16 units of β-glucosidase, 2 units of α-arabinosidase, and 4.5 units of α-rhamnosidase per gram of bentonite were immobilized.

Further research into the aerobic degradation of n-alkanes in a heavy oil by a pure culture of a Pseudomonas sp

Abstract The microbial degradation of the saturated fraction of a heavy oil was examined in aerobic conditions employing a pure culture of a Pseudomonas sp. isolated from soil. A new model of n -alkane degradation is proposed. The n -alkanes were divided into three degradation groups: i) liquid n -alkanes, C12C16; ii) low solid n -alkanes, C17C28; iii) high solid n -alkanes, above C28. Our results show that n -alkane degradation depends on chemical and physical factors such as solubility and surface tension.

Dibenzothiophene biodegradation by a Pseudomonas sp. in model solutions

Abstract The presence of fatty acid and an n -alkane may affect the biodegradation rate of aromatic sulphur compounds such as dibenzothiophene (DBT). A fatty acid (hexadecanoic acid) may form micellar structures favouring DBT bioavailability. n -Alkanes, such as n -dodecane or n -hexadecane, form a film around the aromatic sulphur molecule as a consequence of solvation, thus increasing DBT bioavailability. The mass-transfer rate from the solid to the aqueous phase controls the DBT biodegradation rate when DBT is the only carbon source. Diffusional coassimilation and microbial hydrophobic effects are rate-limiting steps in DBT biodegradation in the presence of aliphatic compounds. Diffusion depends on the DBT concentration in n -alkane, while cometabolism is associated with different n -alkane biodegradation rates. Through the definition of biodesulphurization selectivity and biodersulphurization efficiency, our investigations have shown that a selective aerobic biodesulphurization process is possible by using an unselective biocatalyst, such as a Pseudomonas sp.

Whole cell biocatalysis for an oil desulfurization process

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. Various attempts have been made to develop biotechnological processes based on microbiological desulfurization employing aerobic and anaerobic bacteria. In order to obtain a biodesulfurization process competitive with the chemical-physical one of hydrodesulfurization (HDS), a biotechnological process has to follow the three main refinery steps: 1) separation, entailing some pretreatment of crude oil; 2) conversion, i.e. biocatalytic transformation where the biocatalyst favours a selective desulfurization process without destroying useful products; 3) finishing, in which the crude oil is separated from the biocatalyst and the byproducts. Biocatalysis may be carried out using whole cells or isolated enzymes in the free or immobilized form. The use of isolated enzymes is advantageous since it avoids the formation of undesirable byproduct mediated by contaminating enzymes as in the case of the aerobic biodesulfurization, which is not a selective process. In fact, the aerobic microorganisms may degrade almost all the compounds which make up the heavy oil. However, despite this advantage, extraction and purification of the enzyme is costly and, frequently, enzymes catalyzing oxidation-reduction reactions require enzyme cofactors which must be regenerated after the reaction. For these reasons, metabolic conditions can often be designed by using whole cell biotransformations to promote cofactor regeneration, thus avoiding the problems associated with cofactor recycling and regeneration. Today, the main limitations for the industrial application of a biodesulfurization process are associated with the high cost of the biocatalyst and with the volumetric ratio between the organic phase and the aqueous one. In order to overcome these problems, cell immobilization is one of the most promising approaches in terms of treatment costs and in finishing step times when compared to a continuous stirred tank bioreactor for the biodesulfurization process.

Specificity of an o-diphenol oxidase from Prunus avium fruits

Abstract An o -diphenol oxidase extracted from sweet cherry fruits ( Prunus avium ) was purified 17-fold, and the recovery of enzyme activity was 5·6%. The optimum pH with catechol as substrate was 4·2. The enzyme exhibited only catecholase activity and was inactive with monophenols. The specificity of the enzyme toward 19 substituted catechols was examined. Substituents in position 3 caused a decrease in the affinity for the enzyme, probably due to steric hindrance. Electron-donating substituents in position 4 enhanced enzymic activity, whereas electron-attracting substituents in the same position reduced or eliminated the oxidation.

The effect ofn-alkanes in the degradation of dibenzothiophene and of organic sulfur compounds in heavy oil by aPseudomonas sp.

SummaryThe microbial degradation of organic sulfur compounds was examined in aerobic conditions employing a pure culture of aPseudomonas sp., isolated from the soil. The effect ofn-alkanes on the degradation of dibenzothiophene (DBT) showed that the assimilation of the sulfur compound by the microorganism is favoured byn-dodecane. Moreover, the saturated fraction was seen to enhance the degradation of the sulfur compounds to be found in a deasphaltenated heavy oil.

Preparation and properties of an immobilized soluble-insoluble pectinlyase

Abstract An endo-pectinlyase present in a commercial mixture was immobilized on EUDRAGIT L100-55, a polymer which is reversibly soluble-insoluble depending on the pH of the medium. The enzymic activities of biocatalytic matrices, obtained by pre-activating the polymer either with water-soluble carbodiimide or by simple adsorption, were compared. The biocatalyst obtained by adsorption showed an enzymic activity higher (500 E.U. g −1 ) than that obtained using the activated polymer (50 E.U. g −1 ). Moreover, the activating agent did not seem to be necessary in order to stabilize the interaction between carrier and protein. In fact about 80% of the initial activity was detectable on both matrices after repeated washings with NaCl 0.2 m . The immobilization procedure did not alter the main biochemical parameters of the immobilized enzyme with respect to its native form and appreciably enhanced its stability in the temperature range 25-45°C.

Core-shell functional microspheres by dispersion polymerization: 2. Synthesis and characterization

Abstract Polystyrene microspheres ranging in diameter from 3 to 10 μm were prepared in alcoholic media by dispersion polymerization of styrene in the presence of a methacrylic acid/ethyl acrylate 1:1 statistical copolymer (Eudragit) as the stabilizer precursor. The effects of the initial Eudragit and free radical initiator concentrations on the microsphere dimensions, the microsphere size distribution and surface functionality were investigated. The particle dimensions were found to increase with increasing initiator concentration and decrease with increasing steric stabilizer precursor concentration. The percentage Eudragit in the microspheres was found to increase with the stabilizer precursor concentration and decrease with the initiator concentration. The resulting double-shell microspheres, with specific surface functionalities, are promising as tailor-made supports for biocatalysts.

Barrier and carrier effects of n-dodecane on the anaerobic degradation of benzothiophene by Desulfovibrio desulfuricans

Summaryn-Alkanes affect the degradation of aromatic sulfur compounds both in aerobic and in anaerobic conditions. Some authors have reported anaerobic desulfurization by sutfate-reducing bacteria. These catalytic reactions are biphydrodesulfurizations (BHDS). n-Dodecane has a barrier or carrier effect on benzothiophene degradation in the absence (growing cell condition) or presence (resting cell condition) of hydrogen in the head space of the batch. In addition, thermodynamic factors are very important in benzothiophene and dibenzothiophene degradation by the microorganism Desulfovibrio desulfuricans.

Pyrolysis gas chromatography-mass spectrometry for the identification of anthocyanins

Abstract A new method is described for the rapid qualitative identification of anthocyanins which is based on recognition of differential features of the individual pyrograms and identification by gas-liquid chromatography coupled with mass spectrometric analysis.