A hybrid pretreatment strategy for delignification of Aloe vera processing waste and its effectiveness towards saccharification

A copious amount of rigid Aloe vera leaf rind (AVLR) has been produced from the aloe gel processing industries are majorly disposed as wastes since it has no commercial value. The cell wall compositional analysis revealed that significant quantity of cellulose (46% ± 0.76, w/w) and hemicellulose (18.5% ± 0.24, w/w) which justifies as potent source for bioethanol production. However, high lignin content (13.95% ± 0.45, w/w) hinders depolymerization of polysaccharides into fermentable sugars and subsequent fermentation for ethanol production. In the present study, microwave-assisted alkali (MAA) pretreatment of AVLR was performed by varying the power level (160 W, 320 W and 480 W) which showed a maximum delignification (66.38%) at 320 W. Scanning Electron Microscope (SEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD) based characterization were performed to study the extent of delignification in AVLR biomass. The Gas Chromatography-Mass Spectrometry (GC-MS) analysis was performed for the liquid hydrolysate obtained after MAA pretreatment at 320 W indicated that the hydrolysate contained more of oxidized phenolic hydrocarbons that can be potentially utilized for other value-added product synthesis. A comparison of saccharification efficiency was performed using two different cellulase producers namely Aspergillus niger and Aspergillus sp. A 2.8-fold increase in sugar yield was achieved by Aspergillus sp., with a maximum saccharification of 68.5% ± 0.34 on comparing with untreated AVLR biomass. This indicates the feasibility of MAA pretreatment for AVLR biomass in order to improve the accessibility of fermentable sugars available for ethanol production.