A novel chitosan derivative to immobilize alpha-L-rhamnopyranosidase from Aspergillus niger for application in beverage technologies.

alpha-L-rhamnopyranosidase (Rha, EC 3.2.1.40) is an enzyme of considerable importance to food technology in increasing the aroma of wines, musts, fruit juices and other beverages. The aim of this research is the immobilization of the Rha contained in a commercial preparation already used in the winemaking industry and purified in the manner described in a previous study [1]. The immobilization supports tested were chitin, chitosan and derivatized chitosan, diethylaminoethyl chitosan (DE-chitosan) never previously used for this type of application. Particularly, on DE-chitosan, the Rha was adsorbed and cross-linked with various bifunctional agents (glutaraldehyde, diepoxyoctane, suberimidate and carbodiimide), whose best results (immobilization yields and activity) were obtained with carbodiimide (EDC) that allowed a reduction in the involvement of the enzyme amine groups that are probably important in catalytic mechanism. In addition, the use of rhamnose and a succinimide (NHS) during cross-linking enhanced the action of the EDC and so increased the immobilization yield and activity. The immobilized Rha retained the kinetic parameters (K(m) and V(max)) of the free enzyme and increased stability. Moreover, this biocatalyst allowed an increase in the aroma in a model wine solution containing glicosidic precursors with a marked reduction in specificity toward tertiary monoterpenols as compared to the free enzyme.

Fining treatments of white wines by means of polymeric adjuvants for their stabilization against browning.

Browning and maderization represent important problems for white wine stability. Essentially, this is due to polyphenol oxidation in the wine. The problem has been remedied by adsorption of polyphenol compounds with polymeric adjuvants (chitosans, scleroprotein, and polylactic acid) not used traditionally in wine-making. In particular, some chitosans reduced the polyphenol content and stabilized two Italian white wines (Trebbiano and Albana) to the same extent as did potassium caseinate, an adjuvant normally used in enology. Moreover, chitosans could be reused after a simple regeneration process.

Foliar application of selenite and selenate to potato (Solanum tuberosum): effect of a ligand agent on selenium content of tubers.

The effect of a foliar spray of selenium on potatoes was investigated for 2 years. Amounts of 0, 50, and 150 g of Se ha(-)(1) were applied both as sodium selenate and as sodium selenite in water, either pure or with the addition of 0.15% of soluble leonardite as a source of humic acids (pH 7). Tuber selenium concentration increased with the application levels, both with sodium selenate and with sodium selenite, when only aqueous solutions were used. When humic acids were added, the tuber selenium level rose more markedly after the application of sodium selenate as compared to the case of the aqueous solutions; however, in the case of sodium selenite, the level showed a large increase only after the application of 50 g of Se ha(-)(1). Kinetics showed that humic acids raised the selenate availability, but no differences were found in the distribution of selenium in the tuber fractions. Foliar application of selenium with humic acids was proven to be a good way to increase the selenium content of potatoes, but the assimilation process of selenium was simpler with selenate than with selenite.

Superactivity of peroxidase solubilized in reversed micellar systems.

Vaccinium mirtyllus peroxidase solubilized in reversed micelles was used for the oxidation of guaiacol. Some relevant parameters for the enzymatic activity, such as pH, w(o) (molar ratio water/surfactant), surfactant type and concentration, and cosurfactant concentration, were investigated. The peroxidase showed higher activities in reversed micelles than in aqueous solution. The stability of the peroxidase in reversed micelles was also studied, namely, the effect of w(o) and temperature on enzyme deactivation. The peroxidase displayed higher stabilities in CTAB/hexanol in isooctane reversed micelles, with half-life times higher than 500 h.

Immobilization of endo-polygalacturonase from Aspergillus niger on various types of macromolecular supports.

Endo-polygalacturonase (endo-PG) was immobilized on a wide range of natural and synthetic macromolecular supports and their modified derivatives representing many chemical classes, including esters, amides, phenols, alkyl- and arylamines, and carboxyl derivatives. The immobilization entailed methods of adsorption alone as well as covalent bond formation using glutaraldehyde or carbodiimide or via the diazo-coupling reaction. The most promising system proved to be immobilization on trimalehylchitosan (TMC) via adsorption followed by treatment with glutaraldehyde (GA). The binding capacity of the support is on the order of 13,000 IU/g, half of which is active. Various properties of immobilized endo-PG were evaluated. The optimum pH of the enzyme shifted to the alkaline side. The relative catalytic activity was considerably high even at room temperature and remained so above 70 degrees C. The thermal stability at pH 3-4 was notably improved by immobilization, the half-time doubling. Finally, the apparent K(m) was greater for immobilized endo-PG than for native enzyme, while the V(max) was smaller for the immobilized enzyme.

Stability of glucose oxidase and catalase adsorbed on variously activated 13X zeolite.

The use of 13X zeolite (0.1-0.4-mm granules), treated with 2N and 0.01N HCI, 0.01M citric acid, 0.1M citric-phosphate buffer (pH 3.6), and in untreated form to adsorb glucose oxidase of fungal origin and microbial catalase was examined. Physicochemical analysis of the support demonstrated that its crystalline structure, greatly altered by the HCl and buffer, could be partially maintained with citric acid. The specific adsorption of the enzymes increased with decreasing pH and proved to be considerable for all the supports. The stability with storage at 25 degrees C is strictly correlated with the titrable acidity of the activated zeolite expressed as meq NaOH/g and with pH value of the activation solution. It proved to be lower than 55 h for both enzymes if adsorbed on zeolite treated with 2N HCl, and 15-fold and 30-fold higher for glucose oxidase and catalase adsorbed, respectively, on zeolite treated with the 0.1M citric-phosphate buffer and 0.01M citric acid. The specific adsorption of glucose oxidase and catalase was, respectively, 1840 U/g at pH 3.0 and 6910 U/g at pH 5.0. Their half-life at 25 degrees C with storage at pH 3.5 for the former and at pH 5.0 for the latter was 800 and 1560 h vs. 40 and 110 h for the corresponding free enzymes.