Studies on lignocellulolytic enzymes from spent mushroom straw for bioethanol production
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Date
2019
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Punjab Agricultural University, Ludhiana
Abstract
Spent mushroom substrates (SMS), a lignocellulosic residue of recommended mushroom cultures Agaricus bisporus, Pleurotus florida, Calocybe indica and Volvariella volvacea were evaluated as a fermentable substrate for ethanol production. Activity of Lignocellulolytic enzymes (oxidative and hydrolytic) produced by these four fungal species in SMS at different stages of growth (spawn run, primordial, 1st flush, 2nd flush and end of crop) in nonaxenic and on different interval of days (7th, 14th, 21st and 28th) under axenic condition were evaluated. Considerable amount of oxidative (Lignin peroxidase, Manganese peroxidase, versatile peroxidase and laccase) and hydrolytic (carboxymethylcellulase, xylanase and cellobiohydrolase) enzymes were found in SMS’s. Maximum oxidative enzymes activity was found in SMS of A. bisporus and P. florida whereas, higher hydrolytic enzyme activity was observed in SMS of V. volvacea and C. indica under both axenic and non-axenic conditions. Among oxidative enzymes, maximum specific activity of manganese peroxidase (25.61 U/mg of protein) was found in SMS of A. bisporus at primordial stage and in P. florida (28.89 U/mg of protein) at end of crop on 28th day of incubation. Versatile peroxidase was observed in SMS of all three fungal species except A. bisporus and maximum specific activity value 14.35 U/mg of protein (SMS of V. volvacea) was found at primordial stage under non-axenic condition while 23.33 U/mg of protein (SMS of P. florida) was recorded on 28th day under axenic condition. Lignin peroxidase with maximum value of 8.24 U/mg of protein was found only in SMS of C. indica. Under non axenic conditions, among hydrolytic enzymes, xylanase (21.02 U/mg of protein) was found maximum at end of crop in SMS of V. volvacea while maximum CMCase (32.82 U/mg of protein) was found in SMS of P. florida under axenic condition. These enzymes were partially purified and concentrated by lyophilisation and used for further biological treatment of spent mushroom substrates. Relative proportions of lignocellulosic components (lignin, cellulose, and hemicellulose) were also analyzed. Maximum percent reduction of cellulose and hemicellulose compared to lignin was observed in SMS’s of all three fungal species except A. bisporus in which lignin (43.02%) showed maximum percent reduction. Physico-chemical modifications in SMS were observed by SEM, FTIR and XRD respectively. Biologically pretreated SMS’s were processed for bioethanol production by using two different yeasts i.e. Saccharomyces cerevisiae and Pachysolen tannophilus, and it was also compared with the bioethanol produced from the SMS treated with alkali and partially concentrated enzymes. Maximum ethanol of 13.90 g/l (V. volvacea) and 10.48 g/l (C. indica) were recorded after pretreatment with lyophilized enzymes. According to these results; the spent mushroom substrate of all four fungal species can be a cheap convenient substrate for sustainable production of bioethanol with maximum lignocellulolytic enzymes recovery.
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