Abstract
To sustainably operate a biorefinery with a low cost input in a commercial setting, the hydrolysis of lignocellulosic biomass must be undertaken in a manner which will impart environmental tolerance while reducing fermenter inhibitors from the delignification process. The challenge lies with the highly recalcitrant lignin structure, which limits the conversion of the holocelluloses to fermentable total reducing sugars (TRS). Due to these challenges, sustainable and innovative methods to pre-treat biomass must be developed for delignocellulolytic operations. Herein, Nepenthes mirabilis digestive fluids shown to have ligninolytic, cellulolytic and xylanolytic activities were used as an enzyme cocktail to hydrolyse mixed agro-waste constituted by Citrus sinensis (orange), Malus domestica (apple) peels, cobs from Zea mays (maize) and Quercus robur (oak) yard waste. The digestive fluids contained carboxylesterases (529.41 ± 30.50 U/L), β-glucosidases (251.94 ± 11.48 U/L) and xylanases (36.09 ± 18.04 U/L), constituting an enzymatic cocktail with significant potential for the reduction in total residual phenolic compounds (TRPCs), while being appropriate for holocellulose hydrolysis. Furthermore, the maximum TRS obtainable was 310 ± 5.19 mg/L within 168 h, while the TRPCs were reduced from 6.25 ± 0.18 to 4.26 ± 0.09 mg/L, which was lower than that observed when conventional methods were used. Overall, N. mirabilis digestive fluids demonstrated an ability to support biocatalytic processes with minimised cellulases hydrolysis interference. Therefore, the digestive enzymes in N. mirabilis pods can be used in an integrated system for feedstock hydrolysis in a second generation biorefinery.
Highlights
The challenge associated with environmental pollution and petroleum depletion has ensured interest in the production of biofuels including value-added products using environmentally benign processes
Citrus and oak trees are largely available, focusing on the specification requirements of the feedstock to be used in a second generation biorefinery
The results indicated that the concentration of the pitcher plant’s digestive fluids had a significant effect on the degradation of holocelluloses with the maximum total reducing sugars (TRS)
Summary
The challenge associated with environmental pollution and petroleum depletion has ensured interest in the production of biofuels including value-added products using environmentally benign processes The production of such commodities has demonstrated the feasibility and applicability of biorefinery processes that are microbially mediated, using lignocellulosic biomass feedstock, such as agro-waste, as a primary source of fermentable constituents. Processes 2019, 7, 64 numerous processes to hydrolyse lignocellulosic biomass including agro-waste for biorefineries [1] In these processes, the evaluation focused on reduced hydrolysis time for maximising the extraction of fermentable carbohydrates, reduced energy intensity, environmental benignity by eradicating inorganic compound usage and minimisation of operational costs [2]. These processes, albeit achieving varying successes, include chemical, physical, biological and physico–chemical hydrolysis technologies, either as individualised and/or amalgamated processes [3,4,5]
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