Abstract
BackgroundPrevious research focused on pretreatment of biomass, production of fermentable sugars and their consumption to produce ethanol. The main goal of the work was to economise the production process cost of fermentable sugars. Therefore, the objective of the present work was to investigate enzyme hydrolysis of microcrystalline cellulose and hemp hurds (natural cellulosic substrate) using free and immobilised enzymes. Cellulase from Trichoderma reesei was immobilised on an activated magnetic support by covalent binding and its activity was compared with that of the free enzyme to hydrolyse microcrystalline cellulose and hemp hurds on the basis of thermostability and reusability.ResultsUp to 94% protein binding was achieved during immobilisation of cellulase on nanoparticles. Successful binding was confirmed using Fourier transform infrared spectroscopy (FTIR). The free and immobilised enzymes exhibited identical pH optima (pH 4.0) and differing temperature optima at 50°C and 60°C, respectively. The K M values obtained for the free and immobilised enzymes were 0.87 mg/mL and 2.6 mg/mL respectively. The immobilised enzyme retained 50% enzyme activity up to five cycles, with thermostability at 80°C superior to that of the free enzyme. Optimum hydrolysis of carboxymethyl cellulose (CMC) with free and immobilised enzymes was 88% and 81%, respectively. With pretreated hemp hurd biomass (HHB), the free and immobilised enzymes resulted in maximum hydrolysis in 48 h of 89% and 93%, respectively.ConclusionThe current work demonstrated the advantages delivered by immobilised enzymes by minimising the consumption of cellulase during substrate hydrolysis and making the production process of fermentable sugars economical and feasible. The activity of cellulase improved as a result of the immobilisation, which provided a better stability at higher temperatures. The immobilised enzyme provided an advantage over the free enzyme through the reusability and longer storage stability properties that were gained as a result of the immobilisation.
Highlights
The increasing global dependence on fossil fuels, combined with their increasing cost and gradual depletion, is driving the search for alternatives to fossil-based energy sources
The hemp hurds used in the present study were composed of 77% holocellulose, 8 to 10% total solids and 13% moisture
The pretreatment resulted in superior hydrolysis of the biomass during enzyme saccharification to produce reducing sugars [10]
Summary
The increasing global dependence on fossil fuels, combined with their increasing cost and gradual depletion, is driving the search for alternatives to fossil-based energy sources This search has resulted in growing interest in the production of ethanol from lignocellulosic biomass, a natural and renewable agricultural and industrial waste product [1] whose cellulosic polymers can be converted into fermentable sugars to produce ethanol [2]. Biomass is available in the form of hardwoods and softwoods, and agricultural and industrial waste [7] The use of these renewable, readily available and noncompeting fuel sources for the production of energy presents a solution both to depleting energy reserves and the treatment of existing waste. Cellulase from Trichoderma reesei was immobilised on an activated magnetic support by covalent binding and its activity was compared with that of the free enzyme to hydrolyse microcrystalline cellulose and hemp hurds on the basis of thermostability and reusability
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