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Lipase from Aspergillus niger was obtained from the solid-state fermentation of a novel agroindustrial residue, pumpkin seed flour. The partially purified enzyme was encapsulated in a sol-gel matrix, resulting in an immobilization yield of 71.4 %. The optimum pH levels of the free and encapsulated enzymes were 4.0 and 3.0, respectively. The encapsulated enzyme showed greater thermal stability at temperatures of 45 and 60 °C than the free enzyme. The positive influence of the encapsulation process was observed on the thermal stability of the enzyme, since a longer half-life t 1/2 and lower deactivation constant were obtained with the encapsulated lipase when compared with the free lipase. Kinetic parameters were found to follow the Michaelis-Menten equation. The K m values indicated that the encapsulation process reduced enzyme-substrate affinity and the V max was about 31.3 % lower than that obtained with the free lipase. The operational stability was investigated, showing 50 % relative activity up to six cycles of reuse at pH 3.0 at 37 °C. Nevertheless, the production of lipase from agroindustrial residue associated with an efficient immobilization method, which promotes good catalytic properties of the enzyme, makes the process economically viable for future industrial applications.

ABSTRACT. In this study, mangaba residue (seeds) was used as a substrate for Aspergillus niger lipase production by solid-state fermentation. The partially purified enzyme was efficiently immobilized in a sol-gel matrix by covalent bonding with an immobilization yield of 91.2%. The immobilized biocatalyst and free lipase had an optimum pH of 2.0 and 5.0, respectively. However, greater stability was obtained at pH 4.0 and 7.0, respectively. The biocatalysts showed stability at the optimum temperature of 55°C, where the residual activity was above 87% after 240 min., of incubation. The lower deactivation constant (k d ) and higher half-life of the immobilized biocatalyst indicated greater thermal stability than those obtained with the free enzyme. The Michaelis Constant (K m ) (77 and 115 mM for free and immobilized lipase, respectively) and maximum reaction rate (V max ) (1250 and 714 U mg -1 for free and immobilized lipase, respectively) indicated that the immobilization process reduced enzyme-substrate affinity. Regarding the operational stability, the biocatalyst showed relative activity above 50% until seven cycles of reuse in olive oil hydrolysis. This novel biocatalyst obtained from a tropical fruit residue showed biochemical characteristics that support its application in future biocatalysis studies.Keywords: fruit residue, sol-gel, biotechnology, enzyme.Lipase de Aspergillus niger obtida a partir da fermentação do resíduo de mangaba: caracterização bioquímica das enzimas livre e imobilizada em matriz de sol-gel RESUMO. Neste estudo, o resíduo de mangaba (sementes) foi utilizado como substrato para a produção de lipase de Aspergillus niger por fermentação em estado sólido. A enzima parcialmente purificada foi eficientemente imobilizada em matriz de sol-gel por ligação covalente visto que o rendimento de imobilização foi de 91,2%. O biocatalisador imobilizado e a lipase livre mostraram pH ótimo de 2,0 e 5,0, respectivamente. Entretanto, a maior estabilidade foi obtida nos pHs 4,0 e 7,0, respectivamente. Os biocatalisadores mostraram estabilidade na temperatura ótima de 55°C em que a atividade residual foi superior a 87% após 240 min., de incubação. A menor constante de desativação (k d ) e o maior tempo de meia-vida do biocatalisador imobilizados demonstraram maior estabilidade térmica do que a obtida pela enzima livre. Os parâmetros constantes de Michaelis (K m ) (77 e 115 mm, para as enzimas livre e imobilizada, respectivamente) e velocidade máxima de reação (V máx ) (1250 e 714 U mg -1 , para as enzimas livre e imobilizada, respectivamente) indicaram que o processo de imobilização reduziu a afinidade enzima-substrato. Em relação à estabilidade operacional, o biocatalisador demonstrou atividade relativa acima de 50% até sete ciclos de reutilização na hidrólise do azeite. Este novo biocatalisador, obtido a partir de um resíduo de fruta tropical, apresentou características bioquímicas que justificam sua aplicação em estudos futuros de biocatálise.Palavras-chave: resíduo de fruta, sol-gel, biotecnologia, enz...

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