Abstract
We used a ligninolytic strain of the white-rot fungus B. adusta CCBAS 930 and its mutants with modified ligninolytic activity to assess their potential to remove of molasses. The analyzed strains have been shown to be able to decolorize 1% or 2% molasses solutions containing brown-colored toxic melanoidins. It was found that the decolorization process was determined by the transition to the stage of production of sporulating aerial mycelium (liquid and agar cultures) coupled with an increase in peroxidase activity, which was accompanied by a decrease in the level of melanoidin, free radicals, and phenolic compounds. Four different peroxidase activities were detected in post-culture liquids, i.e. horseradish-like (HRP-like), manganese-dependent (MnP), lignin (LiP), and versatile (VP) peroxidase activities. The HRP-like peroxidase was characterized by the highest activity. The efficiency of removal of melanoidins from a 1% molasses solution by the parental strain and the mutants was dependent on the culture method. The highest efficiency was noted in immobilized cultures (threefold higher than in the mycelium-free cultures), which was accompanied by stimulation of HRP-like peroxidase activity. Mutant 930-5 was found to be the most effective in the decolorization and decomposition of melanoidin. The HRP-like activity in the immobilized cultures of B. adusta 930-5 was 640-fold higher than in the mycelium-free cultures of the fungus. Moreover, decolorization and biodegradation of melanoidin by B. adusta CCBAS 930 and 930-5 was coupled with detoxification.Graphic abstract
Highlights
IntroductionBeet molasses is a sugar industry by-product containing from 48 to 50% of sugars (sucrose, glucose, fructose, raffinose) nitrogen compounds, organic acid, amino acids etc. (Miranda and Benito 1996; Kotzamanidis et al 2002)
Beet molasses is a sugar industry by-product containing from 48 to 50% of sugars nitrogen compounds, organic acid, amino acids etc. (Miranda and Benito 1996; Kotzamanidis et al 2002)
The present study has shown that the ligninolytic anamorphic soil white-rot fungus B. adusta CCBAS930 strain capable of decolorization and decomposition of browncolored humic acids and alkaline lignin derivative
Summary
Beet molasses is a sugar industry by-product containing from 48 to 50% of sugars (sucrose, glucose, fructose, raffinose) nitrogen compounds, organic acid, amino acids etc. (Miranda and Benito 1996; Kotzamanidis et al 2002). The annual sugar production in Poland is estimated at 1700 thousand tons (Kowalczyk-Juśko et al 2014), which is associated with production of 510 thousand tons of molasses. As reported by Guc and Erkurer (2017), the annual production of beet molasses in Turkey in 2014 exceeded 710 thousand tons. In Polish distilleries, approximately 15% of beet molasses are used for production of ethanol (Grajek et al 2008). Another application of molasses in the fermentation industry is the production of organic acids, i.e. oxalic, citric, lactic, and acetic acids (Gur et al 2001; Kotzamanidis et al 2002; Guc and Erkmen 2017), and amino acids (Kahraman and Yesilada 2003). Molasses is a raw material for production of feed and baker’s yeast in the yeast industry (Kahraman and Yesilada 2003; Li et al 2015)
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