Abstract
Enzymatic hydrolysis of cellulose-containing raw materials, using Aspergillus niger, were studied. Filter paper, secondary cellulose-containing or starch-containing raw materials, miscanthus cellulose after alkaline or acid pretreatment, and wood chip cellulose, were used as substrates. The study focused on a wild A. niger strain, treated, or not (control), by ultraviolet (UV) irradiations for 45, 60, or 120 min (UV45, UV60, or UV120), or by UV irradiation for 120 min followed by a chemical treatment with NaN3 + ItBr for 30 min or 80 min (UV120 + CH30 or UV120 + CH80). A mixture of all the A. niger strains (MIX) was also tested. A citrate buffer, at 50 mM, wasthe most suitable for enzymatic hydrolysis. As the UV exposure time increased to 2 h, the cellulase activity of the surviving culturewas increased (r = 0.706; p < 0.05). The enzymatic activities of the obtained strains, towards miscanthus cellulose, wood chips, and filter paper, were inferior to those obtained with commercial enzymes (8.6 versus 9.1 IU), in some cases. Under stationary hydrolysis at 37 °C, pH = 4.7, the enzymatic activity of A. niger UV120 + CH30 was 24.9 IU. The enzymatic hydrolysis of secondary raw materials, using treated A. niger strains, was themost effective at 37 °C. Similarly, the most effective treatment of miscanthus cellulose and wood chips occurred at 50 °C. The maximum conversion of cellulose to glucose was observed using miscanthus cellulose (with alkaline pretreatment), and the minimum conversion was observed when using wood chips. The greatest value of cellulase activity was evidenced in the starch-containing raw materials, indicating that A. niger can ferment not only through cellulase activity, but also via an amylolytic one.
Highlights
The development of efficient methods for the production of biofuels is becoming increasingly important, due to the depletion of fossil fuels and the environmental conditions that are associated with their extraction
Data are presented as median ± standard deviation (n = 3)
The 50 mM citrate buffer was found to be more suitable for enzymatic hydrolysis with A. niger, and this advantage was noticeable after 48 h of hydrolysis
Summary
The development of efficient methods for the production of biofuels is becoming increasingly important, due to the depletion of fossil fuels and the environmental conditions that are associated with their extraction. Possessing environmental and economic advantages, bioethanol is able to compete in the global fuel market. It can be used alone or as an additive to gasoline [1]. Bioenergy production has significantly increased in the recent decades, as part of the transition to a carbon-neutral energy system, and its growth is expected to continue, in the form of biofuels such as bioethanol. The global market is forecasted to increase the share of bioethanol production from the current 2% to 27% by 2050 [2]. Russian biofuel production is only inthe pilot stage [7]
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