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

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 beta-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.