Screening of Fungi From the Trichocomaceae Family (Aspergilli and Penicillia) in Production of Hexose Sugars From Agro-Waste

Abstract

As an alternative to crude oil, the production of hexose sugars from agro-waste may be viewed as an environmentally benign process for sustainable chemicals/fuels production. A range of high-value industrial chemicals and fuels can be accessed from biomass-derived hexose sugars. This work evaluated the production of hexose sugars from yam peels (agro-waste) via enzymatic hydrolysis using different fungi from the trichocomaceae family namely, Aspergillus niger, Aspergillus tamari, Pencillium citrinum, and Penicillium chrysogenum respectively. The agro-waste (yam peels) samples were inoculated directly with the respective fungi without any form of pre-treatment. Hexose yields of 8.75±0.07%, 8.10±0.07%, 2.75±0.25% and 2.75±0.25 were obtained for A. niger, A. tamari, P. citrinum, and P. chrysogenum respectively when the samples were sterilized for 20 minutes at 121oC. Under the same experimental conditions, the control sample gave a minimal yield of 1.50±0.35%. Regardless of the enzyme employed, the amount of hexose sugars produced increased steadily with an increase in sterilization time (40, 60, 80, and 100 minutes). Optimum hexose yields of 16.90±0.71%, 15.50±0.35%, 7.00±0.01%, 7.00±0.05% were recorded for A. niger, A. tamari, P. citrinum, and P. chrysogenum respectively at 100 minutes sterilization time. Generally, P. citrinum, and P. chrysogenum gave similar but low hexose yields while A.niger and A. tamari afforded high and distinct hexose yields. Amongst the different fungi screened, A. niger was the most efficient enzyme for the hydrolysis giving the highest hexose sugar yields under the different conditions employed. The performance of the different fungi was evaluated against three different concentrations (0.5M, 1.0 M, 1.5M) of HCl and H2SO4 acid-catalysed hydrolysis of the yam peels respectively. At 1.0 M concentrations HCl and H2SO4 respectively, the hexose yields of 6.40 ± 0.40 % and 7.60 ± 0.20% obtained were on par with those obtained for the enzymes P. citrinum (7.00±0.01%) and P. chrysogenum (7.00±0.05%) after 100 minutes sterilization time. Regardless of acid concentrations, A. niger, and A. tamari enzymes were more effective for the hydrolysis than the HCl and H2SO4 acid-catalysed process with A. niger being the most effective for the hydrolysis. Therefore, a combination of the A-niger and any heterogenous green catalyst is a promising strategy for further transformation of hexose sugars obtained from agro-wastes to higher value chemicals like levulinic acid in a one-pot synthesis. The extended sterilization time may also be a suitable pre-treatment alternative to mineral acids.