Invertase production and molasses decolourization by cold-adapted filamentous fungus Cladosporium herbarum ER-25 in non-sterile molasses medium

Abstract

This study was undertaken to remove the coloring compounds of molasses as well as produce extracellular (exo) invertase in sterile and non-sterile molasses medium by using cold-adapted filamentous fungus Cladosporium herbarum ER-25. It was determined that a combination of low culture pH (5.5), temperature (20°C) and high molasses concentration (6%) could completely prevent undesired bacterial contamination during the cultivation of C. herbarum ER-25. Under the optimized non-sterile culture conditions, the maximum invertase activity (36.1U/mL) was attained after 72h. On the other hand, the fungus could remove toxical dark brown pigments (melanoidins) in non-sterilized molasses medium through biodegradation and bioadsorption mechanisms. A color removal rate of 64.8% in non-sterile medium could be achieved at the end of 144-h cultivation period. It was found that laccase and manganese peroxidase were responsible for biodegradation. No ligninase activity was detected for the fungus during the cultivation. Maximum laccase (4.6U/mL) and manganese peroxidase (3.5U/mL) activities could be reached after 120h. Higher invertase activity and color removal rate were achieved in non-sterilized medium compared to sterilized one. This is the first report on invertase production from cold-adapted microorganisms under non-sterile culture conditions. As an additional contribution, use of cold-adapted fungi for molasses decolourization was investigated for the first time in the present study.