Highly efficient fungal pectinase and laccase producers among isolates from flax retting liquor

Abstract

The retting of flax straw depends on specific enzymes capable to separate the fibers from the plant straw. Among these enzymes pectinase and laccase play the most significant part of the process. In a previous study, the bacterial pectinase was studied to assess its role in decolouring and degumming of flax straw. In this study, the fungal pectinase and laccase were evaluated in relation to the flax retting and fiber quality. Ten fungi isolated were obtained from the flax retting chamber. These isolates were identified to species level by Biolog. The results showed that every isolate belonged to certain fungal species. The species are as follow: Aspergillus terricola, Aspergillus parasiticus, Aspergillus pulverulentus, Cladosporium herbarum, Fusarium udum, Penicillium solitum, Rhizopus microspores, Gliocladium catenulatum, Fusarium culmorum and Aspergillus flavus. Pectinase activity of members of these fungal species was determined using well plate and DNS methods while, laccase activity was assessed by DMP method. The fungal strain Aspergillus pulverulentus, F23 gave the highest pectinase activity. This fungus produced 25.78 pectinase Unit/gram fungal biomass. The fungal strain Fusarium udum, F25 gave the highest laccase specific activity (0.930 U/mg) and resulted in increase of biomass accumulation (2.94 g/l). Strain Aspergillus flavus, F30 was active in producing of both pectinase and laccase enzymes at the same time. The specific activity of these enzymes was 89.54 and 0.840 U/mg respectively. The fungal specific activities of pectinase and laccase were determined throughout 15 days of incubation. The highest pectinase activity was noted with Aspergillus pulverulentus after 4 days of incubation resulting in pectinase specific activity of 2.265 U/ml, whereas this fungal strain and Fusarium udum, F25, were the highest in laccase production after 4 days of incubation. Optimization pectinase enzyme production was performed in relation to media pH and temperature of incubation. The storage stability of pectinase was also assessed.