Banca de DEFESA: JULIA MARIA DE MEDEIROS DANTAS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : JULIA MARIA DE MEDEIROS DANTAS
DATE: 22/11/2019
TIME: 14:00
LOCAL: Auditório NUPEQ
TITLE:

Chitosan hydrolysis by immobilized chitosanases and non-specific enzymes.

KEY WORDS:
PAGES: 87
BIG AREA: Engenharias
AREA: Engenharia Química
SUMMARY:

Chitoligosaccharides (COS), products of chitosan hydrolysis, have high added value due to their bioactive activities. Hydrolysis can be performed by acid, however this method requires high temperatures and does not have a large selectivity regarding their size, a key feature for the expression of bioactive activities. Therefore, the use of enzymes for hydrolysis becomes a good option because it requires mild conditions and they cleavage specific bonds. However, process envolving enzymes are quite costly, so it is necessary to implement strategies to reduce the operations costs. Among these, the immobilization stands out as a technique that usually increases thermal and pH stability, in addition to allow recycling. The use of non-specific enzymes can be highlighted as another strategy. Thus, the present study investigated the immobilization of cellulase, β-glucosidase, and chitosanases for chitosan hydrolysis. Prior to these studies, the chitosanolytic activity of non-specific enzymes were evaluated under different conditions, where the highest activity was obtained at pH 6.0 for cellulase and at pH 4.0 for β-glucosidase, both at 55 ^oC. In order to evaluate the potential of enzyme immobilization techniques, experiments were carried out with adsorption on cationic resin Streamline SP and covalents bonds on microparticles of silica-gel. Regarding the adsorption, pH 5.0 favored the immobilization of all enzymes, and in terms of enzyme load, cellulase and quitosanase were favored by the lower enzimatic load (25 U/g) and β-glucosidase was favored by the higher enzymatic load (50 U/g). When analyzing the covalent bonds assays, the enzymes followed the same trend of enzimatic load, but in terms of glutaraldehyde concentration, cellulase and β-glucosidase were favoured at the highest concentration (1.00%), while the chitosanase obtained the best result with the lowest concentration (0.50%). It is noteworthy that thermal stability, pH and recycle tests were performed to determine the best immobilization strategy for each enzyme. Thus, the best immobilization strategy for cellulase and β-glycosidase was covalent bonds, when compared to adsorption, since it favored the stability of both enzymes during recycles (presenting 40% compared with 20% of adsorption for cellulase, and 14.75% against only 5.75% in the adsorption system for β-glycosidase). Finally, both immobilization strategies were feasible for increasing the stability of chitosanase, but adsorption showed a marked increase in performance when compared to the covalent bond strategy when considering the 65.00% of the initial activity at the end of the recycle against 44.42% of the covalent system. In the end, all three immobilized enzymes were successful in chitosan hydrolysis.

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