Mesta (Hibiscus spp.) – a potential feedstock for bioethanol production

ABSTRACT

Mesta crop biomass is one of the unexplored lignocellulosic feedstocks for second-generation bioethanol production. The compositional analysis of two mesta species, namely Hibiscus sabdariffa and H. cannabinus were carried out which revealed that the mesta contains 41.89–46.50% cellulose that can be saccharified to release fermentative sugar. Among different physical and physico-chemical pretreatment methods employed, cold alkali (2%) treatment showed maximum cellulose enrichment (38.71%) and significant lignin removal (27.27% of total). Optimization of saccharification process for pretreated mesta biomass was carried out using Box–Behnken design. Based on the observations, use of 4.02% substrate loading, 15.02 FPU/mL of cellulase from psychrotolerant Aspergillus niger SH3, and 5.01 IU/gds of β-glucosidase from Pseudomonas lutea BG8, led to 533.25 mg/gds sugar release from the pretreated biomass. Simultaneous saccharification and fermentation was carried out using efficient thermotolerant yeast strain Saccharomyces cerevisiae LN that resulted in 4.1 g/L ethanol production. It can be concluded that mesta crop can be a good source for the production of second-generation biofuel and the ethanol yield can be further improved by use of accessory enzymes and co-fermenting yeast.

KEYWORDS:

• Mesta
• bioethanol
• cellulose
• feedstocks
• Box–Behken
• saccharification
• fermentation

Acknowledgments

We sincerely acknowledge the help rendered by Dr Gautam Chawla, Division of Nematology; Dr Rajesh Kumar, Division of Agricultural Chemicals and Debarup Das, Division of Soil Science & Agricultural Chemistry for SEM, FTIR and XRD facilities respectively.

Additional information

Funding

The authors are thankful to the Indian Council of Agricultural Research, New Delhi for providing fellowship toward the M.Sc. program of the first author and National Agricultural Science Fund (ICAR-NASF) and ICAR-AMAAS for funding the research activities.