Condições operacionais para a produção de pectinases por Aspergillus niger LB-02-SF em cultivo em estado sólido

Abstract

Pectinases are enzymes that promote the deconstruction of pectic substances and stand out among the enzymes of industrial application, mainly in industries that process plant materials. The pectinases production by filamentous fungi can be conducted in solid-state cultivation. The enzymatic activity results are influenced by process parameters variations. In this context, the operational conditions of pectinases production by Aspergillus niger LB-02-SF in solid-state cultivations were evaluated to increase enzymatic productivity and define strategies that facilitate the industrial application of this technology. From the inoculation by spore suspension in the concentration of 7x107 spore/100 g of wet medium (gwm), which is standard inoculum condition, were evaluated: different sizes of spore suspension inoculum (7x104 a 7x108 spore/100gwm), solid vegetative inoculum (50 e 100gwm), and liquid (5 e 10% v/w). In the second stage, the rotating drum bioreactor occupation volume was evaluated against the variation of the mass of solid medium (1100 and 1800gwm) and particle sizes of the solid support (< 1.0 mm and 1.0 - 2.8 mm). From the agitation condition of 1rpm for 5min every two hours throughout the process (standard), different intermittent agitation strategies were evaluated. In the third stage of the work, by-products from the industrial production of juices, dried and ground, were used as pectinase inducers in cultivations in flasks and in a rotating drum bioreactor. In media based on wheat bran and nutrient salts, apple, tangerine, orange, white, and purple grape pomace were evaluated in comparison to the standard medium containing commercial citrus pectin. Variations in inoculum size and type influenced the kinetics of the flasks and rotary drum bioreactor cultivations. Compared to the standard inoculation, in rotating drum bioreactor cultivations, the use of a suspension of 7x104 spore/100gwm, solid (100 gwm) or liquid (10% v/w) vegetative inoculum, provided an increase in pectinase productivity of 48, 42 and 85%, respectively. In the second step, it was observed that the use of larger wheat bran particles (1.0-2.8 mm) combined with a larger mass of medium (1800 gwm) favored the production of pectinases, reaching a Pmax of 66.4 U/gdm (g of dry matter) in 96 hours of the process. Among the agitation strategies tested, the highest enzymatic activity, 99.7 U/gdm, was obtained at 72 hours in the cultivation with standard agitation performed only during the first 24 hours of the process. In this case, the enzyme productivity was twice that achieved compared to the standard condition. In the evaluation of agro-industrial by-products, the use of apple pomace provided the highest enzymatic activity (59.5 U/gdm) among the pomace tested in flasks tests. In the bioreactor cultivations, higher pectinase activity (83.4 U/gdm) was achieved with the medium composed of apple pomace, wheat bran, and nutrient salt solution compared to the value obtained with the standard medium (66.4U /gdm). These results indicate the possibility of using apple pomace for pectinase production in solid-state cultivation. In the evaluation stages developed in this work, strategies were defined that provided an increase in pectinase activity or enzymatic productivity. These conditions may favor the application of this process on a larger scale and reduce the costs of obtaining these enzymes in solid-state cultivation. [resumo fornecido pelo autor]